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March 26 2019

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March 25 2019

Ep. 524: Judging Age & Origins, part 3 – Beyond Our System

We learned how to figure out the ages of objects in the Solar System, now we push out into the deeper Universe. What about stars, galaxies, and even the Universe itself? How old is it?

This episode is part 3 of a series.
In this episode we mentioned donations and tours. Click to learn more!

Download MP3| Download Raw Show with Q&A| Show Notes | Jump to Transcript or Download

This episode is sponsored by: MagellanTV and 8th Light

Show Notes

Gyrochronology – Astrobiology Magazine
Measuring gravity’s pull at the surface of distant stars
Surface gravity along the main sequence. – SAO/NASA ADS


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March 24 2019

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March 23 2019

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March 21 2019

Vacuuming potato-size nodules of valuable metals in the deep sea, and an expedition to an asteroid 290 million kilometers away

Pirate’s gold may not be that far off, as there are valuable metals embedded in potato-size nodules thousands of meters down in the depths of the ocean. Host Meagan Cantwell talks with Staff Writer Paul Voosen about the first deep-sea test of a bus-size machine designed to scoop up these nodules, and its potential impact on the surrounding ecosystem. In an expedition well above sea level, the Hayabusa2 spacecraft touched down on the asteroid Ryugu last month. And although the craft won’t return to Earth until 2020, researchers have learned a lot about Ryugu in the meantime. Meagan speaks with Seiji Sugita, a professor at the University of Tokyo and principal investigator of the Optical Navigation Camera of Hayabusa 2, about Ryugu’s parent body, and how this study can better inform future asteroid missions. This week’s episode was edited by Podigy. Download transcript (PDF) Listen to previous podcasts. About the Science Podcast [Image: Japan Aerospace Exploration Agency; Music: Jeffrey Cook]

March 19 2019

Ep. 523: Judging Age & Origins, Pt. 2 Across the Solar System

Today we push our aging curiosity out into the Solar System to ask that simple question: how old is it and how do we know? What techniques do astronomers use to age various objects and regions in the Solar System?

This is part two of a series.

In this episode we mentioned donations and tours. Click to learn more!

Download MP3| Download Raw Show with Q&A| Show Notes | Jump to Transcript or Download

This episode is sponsored by: KiwiCo and 8th Light

Show Notes

Measuring Stellar Ages
Measuring the Age of a Star Cluster
How do scientists determine the ages of stars?
How to Estimate the Age (and Distance) of an Open Cluster with Amateur Equipment

Thorium, Technetium, Magnesium Hydride, Uranium, Strontium, Rubidium, Neodyium, and other heavy elements and isotopes used for ratios

Meteorites  – can be aged and compared to Earth ratios

Craters – how clear/worn they are determines relative age

Cryovulcanism on Ceres



Fraser: Astronomy Cast Episode 523: Age and Origins, Part 2, The Solar System. Welcome to Astronomy Cast, your weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, publisher of Universe Today. With me, as always, Dr. Pamela Gay, a senior scientist for the Planetary Science Institute, and the director of Cosmo Quest. Hey, Pamela, how are you doing?

Pamela: I’m doing well enough. How are you doing?

Fraser: Yeah, yeah, I know. You scratched your cornea and you are so sad about your scratched cornea.

Pamela: I am. It’s just healing exceedingly slowly. And I’ve hit the point where – the problem is, I have dry eyes. And I have so much ointment in my eyes now that like the whole world is a foggy, slimy thing.

Fraser: Yeah.

Pamela: And I’m just going to embrace the slime.

Fraser: So, I emphasized, of course, that I’m the publisher of Universe Today because I think I broke Twitter on like Wednesday or Thursday by noting that I just got accused again of plagiarizing the scripts for my videos from this website, Universe Today, written by Fraser Cain. So, that’s pretty funny that people don’t realize that I also write all the scripts for the articles and they publish on Universe Today and also on my YouTube channel. It’s all just me, but I’ve got a big piece of news that I want to share – two more pieces of news.

One, I just came back from Calgary. I got a chance to do a big presentation for the Royal Astronomical Society of Calgary, and they were wonderful hosts. It was so great to get on an airplane, fly within Canada, not have to go through a border, not spend 12 hours. It was very civilized, and I had a great time. And it was really nice to be able to connect with a Canadian audience, which I never get a chance to do. So, thank you to the Royal Astronomical Society of Calgary. I had a great time, and I can’t wait to come back.

And the second thing is, tomorrow when we are recording, Saturday, March 23, 2019, will be the 20th anniversary of Universe Today. So, I will have been doing this job for 20 years. Isn’t that crazy?

Pamela: That is amazing.

Fraser: Yeah, yeah. And it feels weird. It feels weird to be wrapping up 20 years of being a science space journalist, and I am having so much fun. I can’t wait to do another 20, 30, 40 years of this. So, stay tuned. All right.

Pamela: And if you have your robot way, you will be doing this into many more millennia.

Fraser: Yeah, a few more billion years. All right. Well, today we pushed our aging curiosity out into the solar system to ask that simple question. How old is it, and how do we know? What techniques do astronomers use to age the various objects and regions in the solar system? What techniques? How do we know how old it is?

Pamela: We calculate it.

Fraser: Where do we start?

Pamela: Basically, I –

Fraser: All right.

Pamela: – this is one of those things where – every day you and I get news stories across our desks along the lines of – this new star cluster that has been found is predicted to have formed a billion years after the universe was created. This globular cluster over here is remarkably young at only 8 billion years. And it becomes one of these, how on earth do they get at all of these different numbers?

Fraser: Yeah.

Pamela: Because it’s not like we can go out and grab a sample of a star and do like we talked about last week and run it through a mass spec and count up the ratio of this isotope to that isotope and get at the date that the star formed. So, that’s not what we do. We’re gonna start with that.

Fraser: No, but I mean, we were gonna try to constrain ourselves to the solar system although, as you said, the solar system does include a star. So, how do you find out how old the solar system is if you can’t sample the star? If you can’t scoop up a chunk of star and ask it how old it is?

Pamela: So, here is where we have to – unlike with trees, where we assume well, when the tree formed, it had this ratio of carbon atoms. Instead, the process that we use for objects in our solar system and that we use with stars at a certain level, cosmochronography, nucleocosmochronography relies on us saying, okay, so when this particular isotope set formed; it had this ratio when it formed. And when we look at an object and we’re able to get at the amount of those atoms in the thing today, that tells us how long since the atoms formed that, that object has been around.

Now, the problem with this is, it doesn’t tell us specifically how long the thing has been around. It tells us how long the atoms have been around. And so, this is sort of a first stab at things. In our solar system, we generally assume that everything is the same age as our Sun. And so, where we start is, let’s look at the Sun using its light, spread that light out as much as possible into a high-resolution spectrum. And then, do the best we can to count atoms by looking to see how many photons they absorbed and emitted. And from that spectral signature, get at it. It’s the same thing in a much more complicated form.

Fraser: Yeah, but I guess the challenge is that if you – like here on Earth, right, if you’re looking at say a tree, you take that tree and you cut it down. You measure the amount of carbon 14 to the nitrogen that it is decaying into. And you know what it should have been when the tree started forming because it pulled that atmosphere out of the air and then started the timer.

Pamela: And to be fair, we don’t cut down trees and age them that way. When we cut them down, we just count their tree rings. It’s a whole lot simpler. But when we find a piece of wood –

Fraser: Find, yeah.

Pamela: – like a Viking ship –

Fraser: Sure.

Pamela: – in ice somewhere, then everything you said is true because Viking ships were made out of wood.

Fraser: Then that’s what we did, right. I can speak for all Canada and say that we don’t cut down trees everywhere, all the time.

Pamela: This episode of Astronomy Cast is sponsored by KiwiCo. Change the way your kids play with KiwiCo. Visit Kiwico.com/astronomy and get your first crate free. That’s K-I-W-I-C-O.com/astronomy for your first crate free. Kiwico.com/astronomy. I don’t have kids, but I like to borrow other people’s kids and inflict science and awesome on them. One thing I’m looking forward to getting to do is playing with a KiwiCo box and seeing what we can build together. These monthly subscription boxes take the hassle out of finding something cool to do and should let us focus on just building something awesome.

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Once again, change the way your kids play with KiwiCo. Visit Kiwico.com/astronomy and get your first crate free. That’s K-I-W-I-C-O.com/astronomy for your first crate free.

Fraser: But the challenge is, if I’m imagining a star being the same thing, then I’ve got some primordial atmosphere, which is like obviously, the stellar nebula, those elements are coming into the star at certain ratios. And then, those elements are decaying at a set rate over the billions of years. We can’t use carbon. We have to use something else, like uranium or whatever.

But in theory, but back to that idea, I can’t just – 1) How do I know what it should have been in the beginning? And 2) I can’t just scoop up a chunk of star, separate out the atoms, and go, count up the uranium, and thorium, or whatever it turns into, and to know what they are. So, how do I know what the initial ratios were supposed to be?

Pamela: Models, and that’s the problem with everything not on the surface of our planet when it comes to trying to figure out the age. You have to do models of, okay, you start with the Big Bang. At the end of the Big Bang, you had this amount of hydrogen, this amount of helium, these trace amounts of lithium, beryllium. And then, you have a generation of stars. After that generation of stars, what is the ratio of atoms you should have had?

Okay, so then you run forward a few more generations of stars. What are the ratios of atoms that you should have had? And it’s these models that are giving us a fair amount of error because these models get us at – what are the initial ratios of these atoms that should have existed in the stars? So, with G-type stars like our Sun, one of the things that we can do that is actually one of the best ways for age-dating a star, is we look at the thorium to neodymium ratio. And this will give us, within 9 and 14 billion years, the age of an older G-type star.

With younger G-type stars, we do have to start looking at things like lead and uranium. When we look at the ratios of these atoms, though, we have to assume that some of the thorium was already there when the star formed. Some of the neodymium was already there when the star was formed. So, we use our models to guesstimate what is the base ratio of these atoms that the star would have had when it formed, just given the universe?

And then, we take a stellar spectrum and you can get at what are the various percentages of the star’s atmosphere, which is generally unprocessed, all the nuclear processes are going on in the core for the most part. There are exceptions. Don’t “at” me. We can get at the ratios by looking at how the atmosphere of the star absorbs certain colors of light. And thorium’s one of those things that the first time I did high-resolution stellar spectroscopy, it became my enemy because it has a lot of different lines. Technetium, also my enemy. All of these higher atomic mass elements have line, after line, after line.

And it’s by very precisely measuring these lines, knowing that different isotopes will appear at slightly different places, measuring the different isotopes very, very carefully. You can do it. I measured magnesium hydride isotopic ratios. I did not enjoy it, but it can be done.

Fraser: Right.

Pamela: By very, very carefully making these measurements, you can start to get at what are the percentages of these different stars in the atmosphere, what are the percentages of these different elements in the atmosphere of the star, by comparing those measured ratios to the model ratios. That difference tells you how much decay has taken place. And you want to do this with as many different elements as you can. So, we look at that thorium to rubidium ratio –
Fraser: Don’t remove that, Susie.

Pamela: – in G-type stars. We then start looking at the ratios of different kinds of uranium, specifically the 235 to 238. We then look at the ratio of uranium 238 to thorium 232. All these different ratios, they all tell us different things. Strontium, rubidium, lead 207 to uranium 235. These are all created in slightly different processes. They all have slightly different errors, but by putting all of them together, you can start to narrow in on what are the ages of things. And for our solar system, we have a sun right there.

Fraser: Right, right. But the thing is, though, is that to be off by factors of billions of years is not great. And yet, I know that our solar system is 4.54 billion years old. So, if that method of dating the sun is so inaccurate, how do we know that number to such level of accuracy?

Pamela: Well, the thing is, if each of these different things is off by a fair amount, but there is only a very narrow overlap in where all of them mesh up, we use that overlap of all of the errors to say this, this must be where it is. And with our Sun, because it’s so close, because it’s so bright, we can split its light up a bazillion times and get very, very fine-grained measurements. And it’s from those fine-grained measurements that we are able to be more precise with our own Sun than we are with anything else.

Fraser: Right. But I guess what I’m driving at is that there’s got to be some other method that astronomers have used to figure out how old things are in the solar system that’s perhaps raining from the sky, falling on our heads all the time.

Pamela: Well, we do use meteorites, yes. And this starts to get us back to exactly what we talked about last week, which is, you take the thing, you pull it apart atom by atom, and you count those atoms to figure out what are the atomic ratios. And here again, you are relying on what do you think the primordial ratios were. What are the present-day ratios in that object? Because it’s a meteor, we know that it hasn’t gone through age processes like a tree has, and this starts to get us at how old do we think the asteroids were, because it’s shards of asteroids that are raining on us. How old do we think Mars is, because it’s shards of Mars raining on us.

And one of the fascinating things about doing this is you correctly get that the Moon is a different age from Mars because it did go through kind of a resetting when the Moon and the Earth evolved out of the proto-Earth and Theia Mars-sized object that hit the proto-Earth and created a great splash.

Fraser: That’s kind of a fascinating idea that if you go back and you look at all of these objects, you look at these meteorites, and they are all – you count up the uranium atoms, and you count up the I don’t know what they became to. I’m gonna guess thorium. Who knows? Something – you count up the output, and then you can say, oh, here’s the ratio, and you know how long. And you have a pretty good idea of what the original ratio was based on, I guess, seeing enough of these, you can sort of triangulate where that initial data set should be, that you’re like oh, you look at a meteorite. You date it. Oh, 4.54 billion years old.

You find another one, oh, 4.54 billion years old. And yet, you bring a rock back from the Moon, and it only tells you, oh, 4 point – I don’t know what the number is – 3, 4.4, or –

Pamela: It’s usually three point something billion.

Fraser: So, and then it is not. And so that you know that something smashed into the Earth, turned this blob that got remixed-up, and then started from scratch again. Started the timer again, which is this just incredible idea that you can find. And so, we would think that if we could find a meteorite that was older than the solar system, for example, that would tell us that it had to have come from outside the solar system.

Fraser: It’s sort of a really amazing technique. And that it’s always the same number.

Pamela: And the amazing thing about the Moon and Mars is we’re actually seeing how old are the different rocks. So, the reason that so many of the Moon rocks are appearing to only be three billion years old is because that’s when the lava that they were made of was produced. So, we’re looking at basaltic rocks that essentially got reset yet again, even though the Moon itself is estimated to be more than four billion years old. So, when you have –

Fraser: It’s the same trick.

Pamela: – lava involved, all bets are off.

Fraser: Yeah, it’s the same trick. You can tell how old lava is here on Earth. You measure the ratio – because it’s freshly-squeezed out onto the surface of the Earth. And then, the same thing on the Moon, it’s gonna be freshly-squeezed out on the surface of the Moon. All right. So, let’s take two, and we’re sort of leading into what is sort of the next part, is actually starting to age and date specific portions of the solar system. So, how do we know how old various parts of the Moon are?

Pamela: Well, this is where, with the Moon, we’re lucky enough that between the Apollo astronauts and the Soviet landers, we have brought back a lot of space rocks. And these space rocks were gathered from a variety of different sites. And those different sites had different densities of craters on their surface. So, when we look at the Moon, you can see there are these great dark seas. There are these lighter regolith, we call that, lighter areas that just have their surface beat to expletive with all the craters that appear.

Different rocks from areas with different densities of craters we find have different ages, where areas that have the fewest craters have the youngest rocks. Areas with the greatest number of craters have the most rocks. And this is because that accumulation of craters on the surface tells us how long that surface has been exposed to the sky.

This is sort of like looking outside. And if you see different accumulations of snow in the winter, where that area of your driveway might have two feet of snow if you’re having a particularly bad weekend, but there is a rectangle next to it that only has like 10 inches. Well, that rectangle –

Fraser: There used to be a car there.

Pamela: – is probably where there was a car.

Fraser: Yeah.

Pamela: Someone moved the car. It’s a freshly-exposed surface, and that freshly-exposed surface has had less time to accumulate snow. Well, with the Moon, it’s not accumulating snow. It’s accumulating craters. And different size craters form at slightly different rates. So, the giant craters, luckily, appear at a slower rate. And then smaller and smaller, more and more common. So, we can sort of zoom in on how old by going to smaller and smaller craters until we start to saturate.

Fraser: And actually, that process isn’t useful here on Planet Earth because of all the weathering processes that are happening, we can only count a few large craters across the surface of the Earth. The rest are weathered and gone. But on the Moon and on Mars, they are just there, and have remained there for billions of years. The processes are very slow or even nonexistent.

Pamela: And one of the other things that blights our planet, because you can look at Mars, and there is plenty of erosion on Mars. But what we have that Mars doesn’t is plate tectonics where we are resurfacing our planet by having one plate dive under another such that there are only small bits and pieces of Canada and western Australia that are truly ancient. And when we go to Mars, we do see areas that are covered in sand dunes, that are constantly eroding due to the weather. But these are smaller regions, and in general, we can use craters to get at the ages of different surfaces.

Fraser: And I would imagine that same technique could be used for some of the cryovolcanism that’s happening out there across the solar system as well.

Pamela: One of the really awesome things about cryovolcanism that I learned from the Ceres results that have been coming out from the Donn Mission is, and we all know this from looking at photos of like Hawaii, volcanoes slump over time when they’re done doing their volcano thing. So, when you have an extinct volcano, it is going to slowly slouch back into the Earth and over time, work its way back towards flat.

Well, it turns out that on Ceres, cryovolcanoes are going to do the exact same thing where we can trace the history of volcanism, cryovolcanism, on Ceres, we think. But looking at all of these different volcano-shaped mounds that have slumped a variety of different amounts, appearing to say that there has been cryovolcanism over time. And it’s traced out different patterns across the surface.

Fraser: So, what are some places in the solar system that, if you could take samples to do some kind of radioisotopic dating, would you love to get your hands on some samples so that you could then answer some questions about some interesting features in the solar system?

Pamela: Oh, man. So, for me, looking at how different objects have been processed over time, being able to go out and grab samples from asteroids at a whole variety of different distances would get two different things for us. It would tell us when they formed, which hopefully should be about the same time for everything.

But it will also tell us what was the ratio of volatiles where stuff formed. And the amount of these atoms that like to go from ice to gas instantaneously, these volatiles, their ratios are different at different distances from the sun, with fewer volatiles being present inside the things that formed near the sun, and more volatiles being present further out. I would love to be able to use volatiles to trace how things moved around after they formed.

So, this double data on where did things form, what were they formed of, will start to help us answer questions about well, when did different parts of the solar system solidify, how much did things move around, and how much have they been processed over time.

Fraser: Yeah, I think about – the correct answer to that question was everywhere, because –

Pamela: Yes, which I do think I said in a roundabout kind of unscientific kind of way.

Fraser: – pretty close, pretty close, yeah. But imagine, if you could take samples of the ice mountains on Pluto and the ice plains to see when the ammonia glaciers formed. If you could take samples from the hills on Titan, and the sand, and the seas of ammonia, if we could go back and seriously take some samples from the surface of Venus to see when some of those features formed and really understand what shut plate tectonics down on that world, it would be incredible.

And yet, each one of those, unfortunately, they are really rough to get to, and we have to send missions that will get down close and dig around in the dirt and do some of this really careful work.

Pamela: And one of the things that we’re able to do here on Earth is ice core samples where we can look at –

Fraser: Oh, yeah.

Pamela: – how old is this glacier versus that glacier by measuring the difference in atmospheric composition that gets trapped in the ice over time. Now, imagine going to Pluto and being able to do ice cores to get at the history of all these different areas.

Fraser: Or Europa.

Pamela: Europa, so many different places. Ice cores of the poles of Mars.

Fraser: Yeah.

Pamela: There is so much out there to be learned, if only we had better low- power, low-energy requirement, completely sterilized drilling equipment.

Fraser: Right.

Pamela: We have none of those things.

Fraser: No, but that would be – and unfortunately, even the plans for sending say probes to places like Europa and stuff involve some kind of nuclear reactor that radiates heat away and melts its way down through the ice, which is not a great way to take an ice sample.

Pamela: No.

Fraser: You want to have a nice clean drill that pulls up your ice samples one at a time. So, literally, this entire solar system, when you think about how busy geologists here on Earth, and hydrologists as they work with ice cores, and water, and samples and people like that, there are scientists who would love to get their hands on every nook and cranny of this entire solar system and grind it, and drill it, and age it, and date it, and figure out how old this stuff is. And to just understand the history and run it all in reverse.

Pamela: And the hope starts to be that we’ll figure out how to build a more, I don’t know, OtterBox coded cube sets for lack of a better way to put it. Cube sets are still fairly fragile, but if we can get them to the point that they can get collided into an asteroid and still come back to Earth healthy, then we can start to imagine sending out small fleets of essentially interplanetary rumbas that go up and grab samples and then fly on home without taking too much damage in the process. We’re just not to that point.

And as long as we have to rely on SUV-sized things that have more mass and thus more momentum to be transferred during a collision, yeah, you’re better off dropping something lightweight than something heavy. So, we need those rumba spacecraft now, please. Please?

Fraser: Yeah, so if anyone is concerned that there won’t be lots of things to study and discover in the future, it will never end. All right. Thanks, Pamela. Did you want to do a Part 3? Are we gonna talk about how old things are outside of the Milky Way, or we’ve got a bit about stars?

Pamela: Oh, yeah. There is so much cool stuff on how to age-date stars beyond our sun.

Fraser: Yeah, and I think about things like pulsars, white dwarfs, exoplanets, and of course, the cosmic microwave background So, who knows how long this is gonna take us? All right, thanks, Pamela.

Pamela: Thanks, Fraser.

Fraser: Before we leave, have you got some names that you want to say?

Pamela: I do. So, as always, we are here thanks to you. It is your generous contributions that allow us to pay Susie, who keeps us organized, keeps our audio edited, and keeps us in line when we wander off like lost children. So, thank you, Susie, and thank you, all of you, for your generous contributions over on Patreon. I am slowly but surely working our way through our backlog of thank yous. And today, I want to give a special thank you to Jos Cunningham, Les Howard, Dana Nori, Kajarten Svere, Helga Bjorkime, Bill Hamilton, Frank Tippin, Greg Thorwall, Richard Riviera, Thomas Sepstrup, Cory Dovall, Sylvan Westby, and Jeff Cullins. Thank you all so much. As they say on NPR, we couldn’t do this without you. So, thank you for donating well, a cup of coffee a month or more to make us happen. Thank you.

Fraser: All right, we’ll see you next week.

Pamela: Bye-bye everyone.

Pamela: This episode of Astronomy Cast is brought to you by 8th Light, Inc. 8th Light is an agile software development company. They craft beautiful applications that are durable and reliable. 8th Light provides disciplined software leadership on demand and shares its expertise to make your project better. For more information, visit them online at www.8thlight.com. Just remember, that’s www.8thlight.com. Drop them a note. 8th Light, software is their craft.

Female Speaker: Thank you for listening to Astronomy Cast, a nonprofit resource provided by the Planetary Science Institute, Fraser Cane, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at Astronomy Cast. You can email us at info@astronomycast.com, Tweet us @AstronomyCast, Like us on Facebook, and watch us on YouTube. We record our show live on YouTube every Friday at 3:00 p.m. Eastern, 12:00 p.m. Pacific, or 19:00 UTC. Our intro music was provided by David Joseph Wesley, the outro music is by Travis Searle, and the show was edited by Susie Murph.

[End of Audio]

Duration: 33 minutes

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March 17 2019

Bonus Episode: Dust with Dr. Paul Sutter


Recorded during the Astrotour to Costa Rica, Fraser talks to Dr. Paul Matt Sutter about the nature of dust and BICEP 2’s claim of discovering primordial gravitational waves.

In this episode we mentioned donations and tours. Click to learn more!

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Show Notes

show notes


Fraser: Hey, everyone, Fraser here. This is a special bonus episode that I did with Dr. Paul Sutter when we were on our Astro Tours trip in Costa Rica. Paul and I got a chance to sit down and talk about the nature of dust and what impact it played on the BICEP2 claim of discovering primordial gravitational waves, and it was a fascinating conversation. Paul was on the team that helped disprove it, and so he had really a front seat to how this all went down.

And I also just wanted to give you an idea, this is sort of the kind of content, the kinds of things that we do, during our Astro Tours. The next cool one that we’re gonna be doing is of course our All-Stars Party, which is gonna be held in June at Joshua Tree. It’s gonna be me, Paul Sutter, Pamela, Skylias, John Michael Godier, and it goes from June 26-30. We’re gonna be staying at this really fancy hotel, and we’re gonna be looking at the stars every night, and we’re gonna be going on all kinds of interesting trips around the area.

So, if you’re interested, go to AstroTours.co/allstars, and you can find out more information. The deadline to sign up is March 26, 2019. And if you went before, and the price seemed a little high, they’ve lowered the price, so it might be in your budget now. So, check that out, AstroTours.co/allstars. All right, onto the interview. So, I’m here in Costa Rica with a whole bunch of my best friends. And of course, another one of my best friends, Dr. Paul Sutter. Paul –

Paul: Just one of many.

Fraser: One of many.

Paul: There’s so many best friends.

Fraser: We just introduced all the other best friends.

Paul: You do realize that “best” is a superlative? There can only be one best friend. You can’t have many. You may have better friends –

Fraser: I just explained that I did.

Paul: Okay, never mind.

Fraser: Never mind. So, the purpose of this, of course, is whenever Paul and I are on one of the Astro Tours, this one in Costa Rica, I like to corner him and grill him on a bunch of astronomy questions, and this is no exception. And so, the topic that I wanted to talk about today, Paul, is dust.

Paul: Dust.

Fraser: And I talk about this all the time, and I usually – like, “gas and dust, gas and dust, gas and dust.”

Paul: Gas and dust. Or dust and gas.

Fraser: Dust and gas, yeah. So, over there, in the beginning, the universe was gas and dust, and then stars formed in regions of gas and dust.

Paul: Dust and…yeah.

Fraser: And planets are obscured by gas and dust.

Paul: Gas and dust.

Fraser: And the discovery of –

Paul: The disk of the Milky Way is full of gas and dust, yeah.

Fraser: And so, this dust, I have no personal experience with it. I’m assuming it’s small. When astronomers are talking about dust, what are they talking about?

Paul: So, are you familiar in general with the concept of dust?

Fraser: I think of smoke from a fire or like a dust storm.

Paul: It’s a bunch of tiny junk.

Fraser: Right.

Paul: All right, it turns out the universe if full of a bunch of tiny junk. We’re talking about little, little molecules of hydrogen, carbon, oxygen bound together. We’re talking about water molecules. We’re talking about carbon elements. It’s all the basic building blocks of you, me, planets, stars but just flung out there. And it’s everywhere. We see it in the solar system. You can actually literally see it. We call it zodiacal light. That’s the reflection of sunlight off of –

Fraser: Dust.

Paul: – dust in the solar system. And these are like micrometeorites, these are molecules, these are just little chains of hydrocarbons. It’s just junk, like someone needs to clean this place up.

Fraser: So, then where do I have to make that differentiation between gas and dust, right? Because again, I just that term “gas and dust, gas and dust”.

Paul: Gas and dust.

Fraser: So, which is the gas, and that’s different from the dust?

Paul: So, usually, the gas is going to be more elemental. It might be pure hydrogen or pure helium. And as soon as you start building more complex molecules, you start making dust because those complex molecules are gonna behave differently. They’re gonna react with light differently, they’re gonna react with each other differently, they’re gonna have different changes in temperature and density when exposed to heat and radiation than gas will. And so, it’s as soon as you start building those more complex molecular chains, you transition from just being a gas to being a dust.

Fraser: So, the idea that you have a dust means that some kind of process has happened. There’s been some intermediate step. And so, what are the sources of this dust that we’re gonna see out there in the universe?

Paul: This dust that we see in solar systems, in galaxies, and even between galaxies comes from everything. So, if you blow up a star, and you have a supernova, and some of those elements escape out into the galaxy or past the galaxy, and they start mixing with other elements, and they start bonding together and forming molecules, you get some dust. If you form planets in a solar system, and a bunch of those planets smash together and spread their bits all over the surrounding part of the galaxy, you get dust. If you process ingredients near a supermassive black hole as material is falling in and grinding against each other and subject to intense heat and pressures, then they get ejected, you get dust.

It’s just the accumulation of all the fun astrophysical processes that can happen inside of a galaxy.

Fraser: And so, I think where dust is quite difficult for astronomers is that it has made a lot of previous discoveries, ended up being wrong because astronomers didn’t understand what the impact of that dust was.

Paul: Yes, exactly. The fundamental problem is if you look at a star, you could pick a star out in the sky and you look at the star, you’re not seeing the pure unadulterated light from that star as it was emitted from its surface. You’re seeing that light after it’s passed through all those lightyears of dust between us and the star, and that dust affects the light. It can scatter it, it can shape it, it can change its polarization, it can change its wavelength, it can shift it around depending on what kind of dust, and how thick the dust, and where the dust is. And so, the light that you’re getting isn’t pure starlight. It’s starlight that’s been filtered through dust.

Fraser: And I guess will an astronomer not know that that dust is there? Do they have techniques to know which of the light is being obscured by the dust and which is the pure starlight that they should be seeing?

Paul: Yes. This is like 95% of astronomy. It is. It’s figuring out what is dust and what is not dust. Thankfully, we have some tools. One, we have physics. We know what the dust itself is made of because we can look at things like the zodiacal light where we know, wow, that light that is reflected light off of dust, so we can capture its properties, we can understand it, we’ve seen what it’s made of. We have laboratories where we try to recreate what interstellar dust or intergalactic dust might look and behave like and understand how light gets filtered through it, and we understand molecules, and molecular interactions, and interactions of molecules with light.

So, we bring all this to bear, and we look at a single star, and I have to say, we do our best to remove the effects of things like dust. Dust is just one of many things you need to remove, but it’s a big thing, and we just do our best to subtract out the effects of the dust. There are different ways to do this astronomically. Say you have two stars that are very, very identical or you know they’re identical, but they’re in different parts of the sky.

Then say one is in a direction perpendicular to the disk of the galaxy and one is in a direction along the disk of galaxy and maybe further away, then you know the one that’s further away in our disk is gonna have to pass through more dust compared to the light from the one that’s nearby and above us, and you can compare those differences and get a handle on what the dust is doing to the light. Once you have that handle, you can apply it to other stars.

Fraser: So, it’s kind of like when you’re looking at the sun at –

Paul: Which you should never do.

Fraser: No. You’re looking at the sun with proper eye protection –

Paul: Thank you.

Fraser: – and when you look at the sun directly up, it looks more yellowy-white, and when you’re looking at it down closer to the horizon, it’s going through more atmosphere, and you’re seeing it more red because more of the other light is getting scattered away.

Paul: That’s a great analogy.

Fraser: And you know that it’s still the same sun. It was the sun high up in the sky and it’s the sun as it’s getting towards sunset, and so it’s what’s going on in the atmosphere in between that’s changing your view.

Paul: Exactly. You’re not seeing the sun. You’re seeing sun plus atmosphere.

Fraser: And then making those two measurements will allow you to figure out how much of what you see of the sun is the atmosphere.

Paul: Exactly. Exactly.

Fraser: But it’s kind of strange that there’s this thing that, as you say, 98% of astronomy that haunts astronomers, that – and we’ll get to this in a little bit here – has ruined potential for winning Nobel prizes, and yet you’ve never actually even touched it. Are there any plans to try and pull some of this material out of the solar system and bring it home?

Paul: Some of the dust in our solar system is of interstellar origin, and we have missions on the International Space Station, I think there was a dust collector on New Horizons if I remember right where it impacted a little gel thing, and we can look at the dust in the outer solar system. And we know that some of it wasn’t born here. It just kinda filtered in because we’re swimming in it. But most of the work of understanding dust, believe it or not, there are some astronomer who are dusty astronomers, who are experts on dust. This is all they do is they like the dust.

That pesky starlight is so annoying they prefer the dust. It’s just by doing astronomy as it’s always done, which is looking at different objects in different wavelengths, in different directions, trying to put all the puzzle pieces together. One of those puzzle pieces is dust.

Fraser: And so, to kinda bring this around, there’s this really big discovery that was announced back in 2014 that they had seen direct evidence of primordial gravitational waves in the cosmic microwave background, and this was the smoking gun for inflation. We’ve talked about this on another episode with Pamela, so I don’t wanna go too deep into this idea, and I’m sure most people listening to this show – I hope – remember this time when it was like, “This is it, Nobel prizes for everybody because we’ve got this confirmation for inflation,” and then it turned out it was dust.

Paul: It was dust.

Fraser: So, can you tell me a little bit because I know you were on the team that detected the dust?

Paul: So, at this time in 2014, I was a member of the Planck collaboration. Planck was a satellite observing the cosmic microwave background in many, many frequencies and doing all sky maps, so doing relatively low-resolution compared to other experiments but doing the whole sky and doing a very, very good job of it. We’re very proud of ourselves.

And we are trying to understand this primordial light, this light that has been around for 13.8 billion years and is filtered through billions and billions of lightyears of dust to get to us. And the dust does a very, very specific thing to microwave light. The dust changes the polarization of the light. Every electromagnetic radiation has two polarizations, and it changes one of the polarizations of it, so it affects it in a very, very subtle way.

Fraser: In that if I looked at the microwave with my 3-D glasses, and my 3-D glasses happened to be space telescopes –

Paul: Yeah, very large.

Fraser: – and my eyes happened to be microwave sensors –

Paul: Microwave sensors, yeah.

Fraser: – then I would see the way the polarization was being changed.

Paul: If I could show you pure, unadulterated cosmic microwave background light and the light that actually reaches your sensors attached to your face, and you would see a little bit of difference because of the presence of dust between you and that light. So, we’re trying to get to that light. We’re trying to understand what the universe was like 13.8 billion years ago, which means we have to remove the effects of the dust. We have to get rid of that.

And us and the Planck collaboration, at the time this announcement was made, we were putting together our first round of results. We had a bunch of data. We had been collecting data for a year-and-a-half. We were doing all the hard work, and it’s a tricky, tricky thing to figure out what’s dust and what’s not dust, but there are many, many papers with very gory mathematical details that have all the recipes you need to pull the dust out of these maps [inaudible] [00:15:12].

Fraser: How to know dust from not dust.

Paul: Exactly. And the BICEP collaboration who made this announcement, they were trying to get at this primordial signal of inflation. That signal that they were looking for can also be generated by dust. The way the dust impacts the cosmic microwave background light mimics the way this primordial inflation thing affects the microwave light. So, if you just see it, you’re like, “Wow, I got a signal.” Okay, are you looking at inflation or are you looking at dust? They had an experiment at the South Pole that was very, very high resolution, super, super detailed but a very, very small patch of the sky because it’s just one telescope sitting down there.

So, they needed to know, in order to do their analysis, they needed to know in this patch of the sky that we’re staring at, what’s the dust in that direction. If I know for sure the dust in that direction, I can pull out the effects of the dust, and if there is any signal of this exotic thing left over, then I know that’s primordial inflation signal. But with their experiment by themselves, they couldn’t figure out the dust. They needed to rely on something like Planck to provide the dust map.

Fraser: Which was doing sort of an all-sky survey of where all the dust was.

Paul: All the dust, all the cosmic microwave background light.

Fraser: And then they could check their little area against the big map and then figure out –

Paul: Exactly. And the reason it needs to be done with Planck and not BICEP is various mathematical reasons. You need the whole sky in order to be able to pull out the dust. So, we were still working – in Planck – we were still working on what’s dust and what’s not dust, but someone gave a presentation at a conference showing a preliminary map of “hey, here’s the dust in the sky in the microwave band”. They technically weren’t supposed to give that slide. It was preliminary.

Someone from the BICEP collaboration took a picture of that slide, used that picture and said, “Aha, here is the dust map. Here is the dust everywhere in the sky, everywhere in our universe.” They took that, folded it into their own analysis, and said, “Okay, we’ve subtracted the dust –”

Fraser: And we’re fine.

Paul: “– and we’re fine, and here’s our primordial signal.” This is like fourth-hand information to me. I’m just repeating rumors, but I think the BICEP people would say this is how it went down. And then they made the big announcement, but 45 minutes later, there was an email from the leads of the Planck collaboration saying, “Okay, Step 1, do not talk to any media. Step 2, we are having a collaboration meeting right now to figure out what’s going on.”

And I remember in the collaboration meeting, the emails, and the conversations, we formed an emergency working group to just figure out what’s going on, like how are they claiming this, where did they get this dust map, everything, and we figured out the source, we figured out what was going on, and the dust map that the BICEP collaboration used was wrong because it was preliminary. We weren’t done yet. We were still fixing all our codes and cleaning everything up. We were cleaning up our dust.

Fraser: Cleaning up your dust, yeah.

Paul: And we weren’t done yet. So, internally in the Planck collaboration, we knew within I’d say a week that the result was wrong but because our analysis wasn’t finished, we couldn’t make that public because we weren’t done. We just knew that their dust map was wrong, but we didn’t have the final dust map. And so, it was another, I think, three or four months before our data and our analysis went public, but we made a special press release that was cleared by the – there was all sorts of hilarious internal politics that went into this saying, “No, sorry, it’s dust. They used the wrong map.”

And this is not the first time that dust has destroyed someone’s scientific discovery, and it won’t be the last. Dust is always there. It’s super annoying unless you’re interested in it, and then it’s the most exciting thing in the universe, but it’s pernicious because dust, like I mentioned, is all sorts of things. It’s all the stuff that’s not gas and not obviously a star or planet. So, it’s like that’s a pretty wide range of things, and all the different things are gonna have different effects on different kinds of light on different wavelengths on different bands in different ways at different temperatures, and it’s a mess.

Fraser: On that note, thank you so much, Paul.

Paul: Astronomy’s hard.

Fraser: I know, I know. Where can people find out what you’re working on?

Paul: They can visit pmsutter.com. That’s my website. It has links to everything I do. You can also follow me on social media, @PaulMattSutter, you can check out askaspaceman.com for my podcast, spaceradioshow.com for my radio show –

Fraser: And if people wanna join us on tours like we’re doing right now –

Paul: You can go to astro.tours.

Fraser: I thought it was astrotours.co?

Paul: It’s both.

Fraser: It’s both, okay.

Paul: I like saying astro.tours.

Fraser: I like astro.tours too. I’m gonna use that from here on out. That’s great. All right, thanks, Paul. And thanks everyone for joining us.

[End of Audio]

Duration: 21 minutes

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March 15 2019

Ep. 522: Judging Age & Origins, part 1 – Earth Rocks

People always want to know how old everything is. And more specifically, they want to know how we know how old everything is. Well, here at Astronomy Cast, it’s our job to tell you now only what we know, but how we know what we know. And today we’ll begin a series on how we know how old everything is.

This is part one of a double episode.

In this episode we mentioned donations and tours. Click to learn more!

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This episode is sponsored by: 8th Light

Show Notes

How do we age Earth rocks?
How Old Is Earth? How Does Carbon Dating Work?
Radiocarbon Dating
Radioactive decay
Uranium to Thorium
How do Geologists know how old Rocks are?


Fraser Cain: Astronomy Cast episode 522. Ages and origins, part one. Fear. Welcome to Astronomy Cast, your weekly facts-based journey through the cosmos where we help you understand now only what we know but how we know what we know. My name is Fraser Cain. I’m the publisher of Universe Today. With me, as always, is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of Cosmo Quest. Hey, Pamela, how you doing?

Dr. Pamela Gay: I am doing okay enough.

Fraser Cain: Yes, yes. You have a scratched cornea. You are in a deeply uncomfortable time right now. Here’s hoping, if we have this conversation next week, you’ll be in less pain.

Dr. Pamela Gay: The show will go on, however.

Fraser Cain: You are the consummate professional. And I’ve got nothing shameless – well, I always have things that are shameless to self-promote, but I just wanted to give a big shout-out to all of the fans who nagged me to continue reading The Three-Body Problem. The first book was The Three-Body Problem. The second book is called The Dark Forest. The third book – I haven’t gotten there yet. I forget what it’s called. Man, The Dark Forest is so good. The Three-Body Problem was fascinating. It’s written in Chinese, and it’s been translated, and so there’s all this stuff you don’t understand just culture wise.

It was definitely a slog for me. But with the second book, I can’t stop reading it. It is just absolutely gripping and compelling and just has some really wonderful ideas. For those of you who are like me and you read the first one, you’re like, “I don’t understand why everyone’s so excited about this book. It’s a mediocre argument for the Fermi Paradox,” get into the second book. It’s so good. I can’t wait to read that and the third one. That’s all. I appreciate everybody telling me to keep going, and I’m so glad I did. That’s it.

Dr. Pamela Gay: Yay.

Fraser Cain: Yay. All right, well –

Dr. Pamela Gay: I’m gonna shamelessly promote he just came back from his astro tour to Costa Rica. We are both going, in June, to Joshua Tree, and you are invited to come with us.
Fraser Cain: You’ve got until March 26th to make a reservation. Prices have been dropped. Less than $2,000.00 a ticket. You should totally check it out. It is a even better deal, and now’s your chance. If you’re worried about the price, it’s far more reasonable.

Dr. Pamela Gay: So, join us in the desert.

Fraser Cain: Yeah. And then I’m sure you’re gonna talk about your trip.

Dr. Pamela Gay: Yes. If you can’t make it in June and you’d rather see the desert in late August when things are, potentially, a little bit cooler, join me on a trip that departs out of Tucson, Arizona and travels up through the canyon lands and eventually makes it to Las Vegas, baby.

Fraser Cain: Right. Go to astrotours.co to see them all. Astro.tours, actually. That’s the new URL, which is even cooler. All right, so people always wanna know how old everything is, and, more specifically, they wanna know how we know how old everything is. Well, here at Astronomy Cast, it’s our job to tell you not only what we know but how we know what we know. Today, we will begin a series on how we know how old everything is. Go.

Dr. Pamela Gay: Okay, so –

Fraser Cain: You picked, what, a meteorite? What was it? You were talking about how old earth rocks are, right?

Dr. Pamela Gay: Strombolites. So, one of the great quandaries and fascinations, to me, that is completely outside of my normal field of study is, how did life on our planet end up going from being little, tiny methanogen bacteria microbes that created methane that, maybe, like life that might exist on Mars, might exist on Titan, to, instead, being oxygen-generating critters, and when did that happen?

And there was recently some new research studying strombolites, which are, essentially fossilized mats from bacteria. It was pushing back the date at which, it looks like, oxygen started to be generated at depth in the seas. And I was like, “How do they know all of these things, and where are the old rocks?” And so, I went down a rabbit hole. And, when I go down a rabbit hole, it’s usually a good topic to talk about on Astronomy Cast.

Fraser Cain: Your rabbit holes get turned into Astronomy Cast topics.

Dr. Pamela Gay: It’s true. It’s true.
Fraser Cain: No, it’s the – it happens to me as well. I think it’s real – people don’t realize that – I would say a good half to three-quarters of the topics are just whatever we are currently incredibly curious about, and so many of the episodes have been from me, and this one is clearly from you.

Dr. Pamela Gay: So, standard disclaimer, I am an astronomer, not a geophysicist, and I learned pretty much everything I know about geophysics from Emily Lakdawalla, [inaudible] [00:05:24] McKinnon, and the internet. So, kudos to all of them and follow them on Twitter. Now, in this case, we are trying to figure out, what are the various ages of different things on earth? And there’s two different ways to go about this.

The first one is this thing is buried under this thing, which is buried under this thing which is buried under this thing. And you assume that the thing that is closest to the surface is the newest, the thing that is under the most layers is the oldest, and sometimes things get tricky because the earth likes to lift things up and sometimes tilt them sideways.

Fraser Cain: Flip them over.

Dr. Pamela Gay: Yeah, yeah. But more or less, when you’re dealing with what’s called sedimentary rock, you assume the relative ages are based on how things are layered on top of each other. And then, as you go digging through them, if you’re dealing with stuff that’s not too old – so, you’re dealing with things that have occurred within the past few thousand years to 70,000 years or so – what you can do is you can go looking for plant material, biologic material – anything that might’ve ingested carbon as part of its growing process – and measure the ratio of carbon-14 to nitrogen-14 because carbon-14 is perfectly happy to, over time, slowly decay into nitrogen.

And you can count atoms and say, “Okay, this is young because it’s all the carbon-14 in the ratio to carbon – the other isotopes of carbon that we normally see in the air. This all makes sense.” Over time, the ratios change. The amount of nitrogen goes up, and so this let’s you figure out the age of things that aren’t that old.

Fraser Cain: Right. Like wood.

Dr. Pamela Gay: But they have to be old enough. When I was a little kid – I’m gonna fess up to this – I was terrified my teachers would figure out I didn’t do my homework on time by carbon dating my pencil lead. I was a weird child. Also, don’t teach eight-year-olds about carbon dating.

Fraser Cain: No, do still. Whatever is the method of discipline that works best – if it’s giving your child a solid understanding in science – then I think that’s perfectly acceptable.

Dr. Pamela Gay: But don’t give them a partial understanding that makes them terrorized that CSI is going to test their homework and make sure that they turned it in on time.

Fraser Cain: Would that work? I don’t think it’s –

Dr. Pamela Gay: For me.

Fraser Cain: I don’t think you could carbon date a pencil accurately enough to know, within a couple of days, if the homework had been done on time.

Dr. Pamela Gay: Well, you can’t because the half life of carbon is 5,730 years, and so you need –

Fraser Cain: And it would only tell you when the pencil was made, not when the lead was put onto the paper.

Dr. Pamela Gay: Exactly, exactly. And so, yeah, yeah, it’s a bit of a problem. So, you can only use things for certain time ranges. So, with carbon, because of its several-thousand-year half-life, you need to be looking at something that’s old so the decay will have had a chance to have been occurring in a reliable way, but it’s not so old that pretty much all of the carbon would’ve gone away completely. So, we’re looking at –

Fraser Cain: The roof beams of a Roman house.

Dr. Pamela Gay: Totally valid.

Fraser Cain: Perfect.

Dr. Pamela Gay: Go for it.

Fraser Cain: Yeah, they’re like 2,000 years old. That’s a little over halfway through the half-life. You’re laughing. Well, no, half-life is 5,700 years.

Dr. Pamela Gay: Yes.

Fraser Cain: So, yeah, a third of the way through the half-life. You could definitely know that that Roman timber was old.

Dr. Pamela Gay: And there’s other methods that we use as well. So, there’s –

Fraser Cain: And, sorry, I apologize, and I don’t wanna stop you on this new thing, but I think exactly how this works is pretty fascinating, and can we just take a second to – how do we know that, when you start the stopwatch with a piece of wood, for example, that gets used in a Roman house – how do we know that that wood started at that time?

Dr. Pamela Gay: When plants grow, they’re actually sucking gasses out of the air to make themselves. If you’ve ever tried to figure out, where does a tree come up with all the materials to make its leaves, its bark, its everything else? Why doesn’t it hollow out the ground beneath it as it sucks up nutrients? Well, it’s because the carbon that makes up the tree is coming out of the air, and the carbon in our atmosphere has specific ratios of the different kinds of carbon atoms that it has, the different isotopes. The carbon-12, the carbon-13, the carbon-14.

And, of course, it has nitrogen and all these other things, and we know a brand-new piece of wood that you’ve just gone out into your backyard and chopped off of your tree is going to have, when you shove it through the mass spectrometer, certain ratios of these atoms. So, new no longer respirating, no longer ingesting from the atmosphere wood is going to have a representative ratio of isotopes and a ratio of the master parent’s atom and daughter element. Now, over time, some of the carbon-14 is gonna be like, “See ya. I’m becoming nitrogen. I’d rather be nitrogen.”

And, through these decay processes, that carbon-14 decreases over time, and the nitrogen increases, and the carbon-12 and 13 are just sitting there going, “But, but, but.” And so, because you see the ratio of one of the forms of carbon changing in relationship to the other types of carbon that became that chunk of wood, that bacteria, that rat – whatever it is that is biological that respirated – that change in the carbons ratios is one side, and the other side is you just count the child elements. Now, the place that the counting of the parent and daughter atoms is most relevant is, actually, when we deal with a different radioisotope dating mechanism, and this is where we look at the decay of uranium into lead. Earth has radioactive materials in it. It’s kind of everywhere. And so, when you grab a piece of rock that isn’t generally being processed, that piece of rock can tell you how old its surroundings are. This is what we refer to as an Ignatius rock. So, we have three kinds of rock. Ignatius rocks, which are formed of stuff, and they sit there going, “Hi, I am a mineral.”

Fraser Cain: I think it’s igneous.

Dr. Pamela Gay: Yes, it is. I said the name of a saint, didn’t I?

Fraser Cain: Probably. So, I –

Dr. Pamela Gay: Let me start that over. Thank you. Good catch. So, we have three basic kinds of rock. The igneous rock is sitting there going, “Hi. I am a rock. I formed. This is who I am. I am happy like this.” We have metamorphic rock that has probably changed over time. And, when you study the ratio of stuff in metamorphic rock, it tells you when that particular rock metamorphosized, came into being versus how old that surrounding is. So, the Ignatius rock – I said it again. The igneous rock will tell you how old the area is. And then we also have sedimentary rock, which we talked about at the beginning of the show.

With that igneous rock, this is where we start figuring out that the Canadian shield parts of Australia, western Australia and bits and pieces of India and Africa are the oldest places in the planet because we look at this uranium-234 that is decaying to thorium-230. We look at other forms of uranium that are decaying into lead via a variety of different decay chains, and we literally just count up, what is the ratio of uranium to lead? What is the ratio of uranium to thorium? And this tells us how old that chunk of rock is, which then reflects how old that chunk of a continent is, which is kind of awesome.

Fraser Cain: But I mean, aren’t those elements – when you think about, say, the thorium, wasn’t that formed in the supernova or colliding neutron – sorry. I’m not sure how far thorium is up there. It’s gotta be beyond iron, though, right?

Dr. Pamela Gay: Yeah.

Fraser Cain: So, weren’t they formed in the supernova? So, how do you know – how can you get any kind of local measurements when it all just came from whenever that supernova was formed, and why can’t you use it to tell you when the supernova happened?

Dr. Pamela Gay: So, one of the great lies that we inadvertently tell is we will say that all of the atoms of gold in that ring you’re wearing were made in a neutron star collision is the new solution. But what we failed to say is that lead, in that pipe that, hopefully, you aren’t using for drinking water, may have come through the decay process of uranium and was not created in the supernova.

So, sometimes the elements that we’re looking at, they weren’t created in a supernova. Their parent atom was created in a supernova. So, here, we know what the background distribution of atoms is on our plant in general. We know what we should expect. And, when we see a concentration of uranium atoms and lead atoms interspersed inside of a rock, that is a reflection of the parent/child atomic decay process, not some supernova.

Fraser Cain: Right, right. But the point being that, for example, with the carbon-14 turning into nitrogen-14, you know the process that came from the air to make the tree, and you know what the ratio was the moment the tree was formed, and then that allows you to then start the clock. Same thing with magma. If you look at a chunk of lava rock, you know what lava of that variety – what mixture of elements should be in that lava of that variety. Knowing what went into it then allows you to measure the constituents, and you can start the clock and figure out what happened.

And so, for every one of these timekeepers, you need to know that starting condition. You need to know what the ratios should have been. But if you just have a blob of uranium, you don’t know what the starting conditions should have been, so you have no way to know when it was created from a – if you just have one atom of uranium or one atom of lead, you don’t know when that atom of lead was formed because it’s all just random probability.

Dr. Pamela Gay: So, if you have a pure block of uranium, you know it’s a baby block because decays haven’t taken place. If you have a block that’s pure lead, you know nothing. If you have a block that is a mixture of uranium and lead, you can generally say, “This used to be just uranium, but it’s been hanging out for this long.” And the thing is, we also use this in concert with other methods, and uranium, in particular, because of all the energy involved in its decay process, does a bunch of really cool things. One of my favorites is what’s called vision tracks, and this is where you measure the damage in volcanic glasses and other naturally occurring glasses and minerals from when uranium-238 decays. So, you will get damage, faults, things you can see in glasses and minerals that contain uranium as a result of the decays, and you count up all of these things, and that tells you how much decay has happened, and that will tell you how old the glass is. There are other minerals that you have the uranium-234 to thorium. You have the uranium-238 going to lead. With all of these different processes, you can count different atoms because, naturally occurring, when you have uranium, it’s not gonna be just a single isotope. It’s gonna start out just like the carbon, with a variety of isotopes together.

So, with these multiple methods all grouped together around one species of atom in all of its isotope varieties, it gives us multiple ways to say, “This is within this age range.” Now, with the uranium series, you are looking, again, at things that are very old. So, here, you’re looking at the hundreds of thousands of years to billions of years. But there’s other ways. There’s, yet, more that uranium is responsible for.

One of the other things I didn’t even know, before prepping for this show that you can do with uranium is, when things get buried either by human beings digging a hole or, in the case of my house, dogs digging a hole and dropping something into the hole and then covering it back up or just wind-blown dust, sand, mudslides – whatever – when something gets buried, it will have experienced a certain amount of radio-induced magnetism. Paramagnetism is the fancy word.

And, if there are mineral lattices, they’re going to be sensitive to this radiation-induced process from uranium. And this what’s called electron spin resonance can be measured and get us a date of something between 1,000 years and 3 million years. So, uranium, it creates paramagnetism that affects lattices. It creates fission processes that create fractures in glass. It just plain decays into things that you can count, and so this one atom is just responsible for so many different ways that we measure the ages of things.

Fraser Cain: And I’m sure we’re going to be taking a look at uranium again as we look at some of the later shows as well.

Dr. Pamela Gay: Yes.

Fraser Cain: And I’m just sort of imagining this sort of rabbit hole. So, did you reach the bottom of your rabbit hole where you were like, “Okay, how did they know?” So, can you sort of go back to that original story that you were talking about and sort of get a sense of how they knew what they knew?

Dr. Pamela Gay: So, the original story was on these fossilized bacteria mats in Australia. And, here, they were looking at a variety of different radio dating mechanism to get at, how long had these things been buried? And they also looked at the sedimentary layers. And one of the things they didn’t use that I learned about in the process of doing this that works with under the ocean in particular is – we’ve talked about the magnetic pulls of the earth flipping before and how this can actually be seen and how lava from the Mariana Trench, from where the sea floor is splitting and oozing out lava and adding more land under the sea – that land under the sea – and, now, I have a Disney song stuck in my head.

Fraser Cain: Yeah, me too. Get it out, get it out.

Dr. Pamela Gay: As it comes out, locks into the sedimentary record, the alignment of the magnetic field of the earth at the moment that it was created, and you can look at the magnetic field in these different rocks as it flips over time and say, “Ah-ha, this belongs to this magnetic field era.” So, you can also do magnetostratigraphy –

Fraser Cain: What?

Dr. Pamela Gay: – which is a fabulous word that I – it’s a new word. I learned a new word.

Fraser Cain: That’s amazing. Right. So, let me see if I understand this correctly. You’ve got the earth’s magnetic field flipping, and, when those flips happen, it’s fairly well known. I know they look at this with looking at ancient lava flow. They can see when the flips happen because the iron crystals are magnetized to align with the magnetic field as the lava is pouring out.

Apologize to everybody who thinks I say lava wrong. I’m Canadian. Different from Ignatius. And so, then all you have to do is look at the alignment in these rocks, and then you just kind of compare to known times that had a similar shape of the various alignments and durations, and you can go, “Oh, this happened during this time period.” That’s mental. I can’t believe that’s possible. That is amazing.

Dr. Pamela Gay: It’s magnetic.
Fraser Cain: It’s magnetic. That’s a stunning accomplishment. And so, it lets you just – if you can get at the magnetic crystals of any chunk of rock and there’s some kind of, I guess, time or you know its orientation, then you can start to puzzle out when this stuff formed. Wow.

Dr. Pamela Gay: It’s called the polarity of the earth’s magnetic field. And, yeah, it’s kind of awesome. And there’s so much cool stuff that scientists have somehow figured out, and, a lot of this stuff, I’m like, “How did you initially think to look at that?” The magnetostratigraphy, actually, that one makes sense, but there are inclusions in quartz crystals – zircons in Australia, for instance, are some of the oldest rocks around, and the Jack Hills zircons date back between three billion and four billion years ago where our planet had survived the thing that created the moon about 4.54 billion years ago. So, these things are like 500 years after the earth came into its current mass amount.

These crystals contain tiny inclusions, gas bubbles, and each little bubble reflect the earth’s conditions at a different point in time. This is the same technique that we use to figure out where in the solar system meteorites come from. Well, it’s also used to figure out when in the earth’s history zircons come from, and that’s just awesome that these things that we use to make jewelry are little time machines that lock in on the history of our own planet.

Fraser Cain: That’s just amazing. Were there any other methods, or do you wanna save this for next week?

Dr. Pamela Gay: There’s one more method to mention, and this one – I have no idea if I’m saying this right, but I’m gonna embrace the mispronunciation. Tephrochronology. This is looking at how volcanic ejecta layer on top of one another and the chemistry of the lava, and this gets used to figure out how different events may or may not be related to one another.

Fraser Cain: That’s really cool. It’s kind of like it’s that same idea of the moon, and you’re counting up craters on the moon and seeing the way the craters are on top of each other, and we actually – we had a project with that on Cosmo Quest.

Dr. Pamela Gay: And we will again. We’re just rewriting our software right now, so stayed tuned, folks.

Fraser Cain: So, is there a volcano mappers coming?
Dr. Pamela Gay: Not that we currently have planned, although, I would love to do that for series, which is apparently covered in cryovolcanoes, but that’s a different quandary.

Fraser Cain: Yeah. So, you could do that, though, right? You could have –

Dr. Pamela Gay: Yeah.

Fraser Cain: – cryovolcanoes. The ejecta would be out there from one volcano, and then another would be over top of it, and then another would be over top of that, and you could sort of detect by counting up the layers of cryovolcanic ejecta.

Dr. Pamela Gay: The other cool thing about this particular technique is there are also the chemistry and the geographic changes that come with volcanoes. When you look at the shape of a volcano, you can say, “Oh, that one’s super tall and still super pointy. It must be still active.”

As they round, as they slump, you can tell they’re older and older. And it’s from that slumping that takes place that you can also tell the ages of the volcanos, especially in series, where the results of the cryovolcanism taking place aren’t necessarily still evidence for the oldest volcanoes or even the medium old volcanoes. So, it’s from the shape of the volcanoes as they slump back into the surface of series that we can start to say old versus new.

Fraser Cain: All right, where do we go next week?

Dr. Pamela Gay: So, next week, we’re gonna talk about things like what I just brought up with on series and work on figuring out, how do we know the ages of things on other worlds? And I don’t know if we’ll get to it next week or if there’ll be a third episode, but how do we measure the ages of stars and other materials in our universe?

Fraser Cain: All the way out to the cosmic microwave background radiation.

Dr. Pamela Gay: Yep.

Fraser Cain: Amazing. I love it. All right, now, we should thank some people.

Dr. Pamela Gay: Yes. Yes, we should. So, we thank a bunch of you for being awesome, and we can’t thank all of you every episode, so I’m working our way down the list of our Patreon followers. If you want to help us pay Suzy, please click on over to patreon.com/astronomycast. This also pays for our server and, generally, just keeps us going because we can’t do it without you. So, special thanks to Dean, Ryan James, Dwyane Isaac, Glen McDavid, Benjamin Davies, Paul Weller, Russel Peto, Dan Littman, Martin Dawson, Kenneth Ryan, Brian Kilby, Steven Ludking, and Thomas Shepshrup. Thank you. Thank you. We are so grateful for everything you have done to make this show possible.

Fraser Cain: Thank you, everybody. And, Pamela, we will see you next week.

Dr. Pamela Gay: Buh-bye. This episode of Astronomy Cast is brought to you by Eighth Light Inc. Eighth Light is an agile software development company. They craft beautiful applications that are durable and reliable. Eighth Light provides discipline software leadership on demand and shares its expertise to make your project better. For more information, visit them online at www.8thlight.com. Just remember, that’s www. the digit 8 T-H-L-I-G-H-T .com. Drop them a note. Eighth Light, software is their craft.

Female Speaker: Thank you for listening to Astronomy Cast, a nonprofit resource provided by the Planetary Science Institute, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at Astronomy Cast. You can e-mail us at info@astronomycast.com. Tweet us @astronomycast. Like us on Facebook and watch us on YouTube. We record our show live on YouTube every Friday at 3:00 p.m. Eastern, 12:00 p.m. Pacific or 1900 UTC. Our intro music was provided by David Joseph Wesley. The outro music is by Travis Sural, and the show was edited by Suzy Murph.

[End of Audio]

Duration: 32 minutes

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March 14 2019

Mysterious fast radio bursts and long-lasting effects of childhood cancer treatments

Host Sarah Crespi talks with Staff Writer Daniel Clery about the many, many theories surrounding fast radio bursts—extremely fast, intense radio signals from outside the galaxy—and a new telescope coming online that may help sort them out. Also this week, Sarah talks with Staff Writer Jennifer Couzin-Frankel about her story on researchers’ attempts to tackle the long-term effects of pediatric cancer treatment. The survival rate for some pediatric cancers is as high as 90%, but many survivors have a host of health problems. Jennifer’s feature is part of a special section on pediatric cancer. This week’s episode was edited by Podigy. Download a transcript (PDF) Listen to previous podcasts. About the Science Podcast [Image: ESO/L. Calçada; Music: Jeffrey Cook] 
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