Daniel and Kelly’s Extraordinary Universe - How old is the earth?

Episode Date: August 6, 2019

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Hey, Daniel, do you keep a family photo album? You know, we used to, but these days it's all digital. I think Mark Zuckerberg, owns all of our family photos. It owns your family period, probably. That too. And how do you feel when you look back and see pictures of yourself when you were younger? I try to ignore all those signs of aging,

you know, pretend that I look the same 10 or 20 years ago as I do today. I see myself as a fine wine. Because you have turned? Because I just get more expensive the older I get for some reason. Well, you know, I've known you for over 10 years or so, and I can say with confidence for those people listening that you are sir, no, Paul Rudd, unfortunately. That's true in many ways, unfortunately.

But it is kind of interesting how little clues can show you how old someone is or how old something is, right? It's true, you know, a few wrinkles here and a few gray hairs there, and all of a sudden you look like you're in your midlife crisis. What's that look? Like a look of panic? It's a look of gravitas. I always remember how Dan Quail died his temples gray

in order to not look so much like a little boy. Dan Quail, man, that's a reference that totally tells everyone how old you are. No, but it's fascinating how almost everything around us ages, right? Everything from people around you to the rocks around you to the buildings around you always show their signs of age. Nothing in this world is permanent. Hi, I'm Jorge, I'm a cartoonist and the creator of PhD comics.

Hi, I'm Daniel. I'm a particle physicist, and I'm young and spry, and I have not written any web comics, but I'm the co-author of the book, We Have No Idea, all about the unknown questions in the universe. And welcome to our podcast, Daniel and Jorge Explain the Universe, a production of I-Hard Radio. In which we take weird and amazing and young and old stuff in the universe and try to explain it to you. And not just telling you the answers, but sometimes digging in deeply and explaining how we know so that you can explain it to skeptical folks around you. Yeah, we try to get you to think about the world around you and even the world you're standing on right now, or sitting on or lying down on. Depending on how you can see in podcasts.

Depending on how old you are. But one of the goals of this podcast is for you to have sort of a new perspective on the world around you. We want you to see everything around you as sort of a clue, something that can tell you how the world works, that can reveal secrets, that can answer questions. Because almost every question we have about the universe, the answers are all around us. And it just takes sort of a trained mind and a careful eye to see those clues everywhere. And so there are clues all around you. about where we come from and how long we've been here and how long everything has been here, right? Yeah, exactly. And sometimes the answers are easy and obvious and sometimes the answers are mind-bogglingly surprising.

And so today on the podcast we'll be tackling quite possibly the oldest question on earth. Would you say that's true, Daniel? Is that who stole my dessert? I think the answer is obvious. Obviously, it's your children. Well, you know, that's actually a question my kids asked me today. when was dessert invented? Oh. Sounds like a topic for a podcast. I don't know if that falls into a physics question,

but it's sort of a fascinating question. And they were actually hypothesizing that dessert might be older than people that maybe like our pre-human ancestors enjoyed a sweet treat after dinner. What do you think? The little bacteria that evolved in the ocean, they're like, you know, I could use

a little tirami suit after consuming this other bacteria. I don't know if we have enough in common with bacteria to say what they might like. But I can imagine some pre-human hominid, you know, eating some berries and going, hmm, that goes nicely with my antelope or whatever they had for dinner. Well, anyway, so what I mean by it's the oldest question on Earth is that it's probably really the oldest question that could be on Earth, right? Yeah, I think that's probably true. And it's an important question, right?

It's the kind of question that we'd like to dig into because it's the kind of question where the answer could change the way we think about life and the universe and the humanity's role in it, right? It has all sorts of things to do with creation and the context of our lives and therefore how we should live our lives and whether they have meaning. And so today on the podcast, we'll be tackling the question. How old is the earth? And is it even polite to ask?

That's right. And what does the earth do when it? gets upset right when he gets offended and not just how old has it had any work done has the earth had any work done is it trying to i think the earth looks great doesn't look a day past four billion um it is full of bulltox though probably right that's true um and and just as important as the question how old is the earth and the answer which is you know just a number is how do we know how do we have confidence in this answer because you know there are people out there who hold beliefs about the various age of the earth.

And one of our listeners actually wrote in and said, hey, could you tell me how we know the age of the earth so that when I discuss it with my friends who have strong opinions about the age of the earth, I can tell them not just what scientists think, but how they know it. Yeah, and that's the thing I think we always try to do in this podcast, right? It is try to get at how people know these things,

not just tell people what scientists know, but how they know it. That's right. And that also helps you understand with what confidence we know it. Like, is this just sort of an energy? educated guess and back of the envelope calculation, or is this something that people have been working on for hundreds of years and we have great confidence and have it nailed down to like 0.01%. And it's important because different things in science are known well

and some things in science are known not very well. So it's important to know how we know. Yeah, and so how old is the earth is the question for today? And it's kind of, I think it's a question most people know a little bit about, right? I mean, I think everyone knows or has a sense that the Earth is very old. Yeah, but you know, that sense that the Earth is like extremely old, like many orders of magnitude older than you or me or your parents, you know, is a fairly modern idea.

I think thousands of years ago, people thought the Earth was only hundreds or thousands of years old. They thought it might have been created fairly recently. And it was only sort of in the 1800s that people started to understand that there were processes around us that we could see, specifically rocks and evolution, so geology and biology, started to give hints that the answer was much, much bigger than anything anybody had imagined. And I think that's wonderful. I love to live in a scientific era like that where something you thought you knew is upended and replaced with a completely different answer that's like, or is a magnitude bigger.

Wow. Is that really true? Like only in the last couple of hundred years, do we have a sense of how old the Earth really is? Before it was totally up in the air? Yeah, it was up in the air until about the 1800s. And then people started trying to do calculations. And they're like, well, how long would it take to form a planet? You know, say you gathered it together with gravity or, you know, how long would it take to lay down layers of rock?

You know, how long would it take glaciers to move, this kind of stuff? And, you know, geology is a fairly young field in that, you know, it's a couple hundred years old. So people started to look around, and as soon as they started to explore these geological processes, they realized, wow, this stuff takes a long time. And, you know, it's sort of like walking into a room and seeing somebody has written a book that's like five million pages long. And you're like, wow, you've been in this room a long time. You know, it shocks you into realizing that things are a much different scale than you imagined. And that's the, we've seen the story the earth all around us. we realize it's staggeringly long, much longer than we imagined.

And that, yeah, that's a fairly new idea. Yeah, that's a lot of party you've missed. Exactly. We showed up at the very end of the party. Things have been around for a long time. Do you have a fear of missing out there? Is it FOMO about what happened in the air? All the good desserts.

I have a fear of being in parties, actually, to be honest. What about all the desserts? They usually have good desserts at parties. All desserts? I just like a fine dessert wine. So you show up at the beginning of a party, have the desserts, drink the wine, and then go home. That's how you know you're old.

Sounds like a good party to me. That is how you know. It's an age-old trick. Exactly. That's very age-appropriate. Notice the beginning of this field, like becoming scientific. Before that, it was just speculation, but the beginning of the field becoming scientific was in the 1800s.

But still, that's very inaccurate. Like, looking at rocks gives you clues about the sort of order of magnitude, but then people wanted to know very precisely. And that took some time to basically to find clocks inside the earth, clocks that have been ticking since it was born. And that's in the end. Signs of aging. Yeah, signs of aging.

Very precise signs of aging that could tell us how old the earth was. So you're saying like the people who started the United States, like the founding fathers, they had no idea how old we've been around? Like did they think we'd been around for a few thousand years? for a few, but didn't they know about the, you know, like ancient Egypt and things like that? Yeah, but, you know, that's thousands of years. And so I think they had the idea that the Earth was, you know, thousands, many thousands of years old, right? Because that's as long as written history is.

And so they imagine it's on that time scale because that's the oldest thing you know. And that's basically the game is like find the oldest thing you know and then assume that that's basically the age of the world, right? And that's frankly what we're still doing, except that we think. that we found stuff that comes from the very beginning of the world. But, you know, they knew about stuff that was thousands of years old, so they had no reason to believe that the earth might be millions or even, God forbid, billions of years old, right? Plus, I think those guys were pretty religious. All right. So it is an age-old question and one that a lot of people have had answers to and seem to have answers to. We were wondering what people out there

right now in the world. Think about this question. Yeah, and this is one, this is a set of interviews. I was very curious to see what people thought. I was wondering if I would run into some sort of young Earth folks who thought the Earth was from biblical ages. And even those people who were scientific, I was wondering, like, how precisely do people know the age of the Earth? So this, I was very fascinated to hear the answers. Like, is it a million years, a bazillion years?

27.2 bazillion. And so as usual, Daniel went out and asked people on the street how old they thought the Earth was. So think about it for a second. If you ran into a physicist in the street today, how would you answer this question? And no Googling. Well, here's what people had to say.

I have no idea. Probably a billion years. I don't exactly. But my understanding is it's a couple hundred million years old. Okay. Do you know how we know? So I don't. Actually, like my physics knowledge is pretty limited.

I think, like, we've used carbon dating to date things within various geological epochs. but I don't actually know how we arrived at the calculation of the Earth's age. A million year? A million years, okay. Maybe three billion years old? Five billion. Tens of million of years? Yeah.

Four billionaires? All right. And how do we know? Rock formation. It's probably like millions of years old, I feel like. All right. A lot of millions and billions, right? Yeah, exactly.

Not a whole lot of really specific answers. I have to say I was a little bit disappointed. And I guess I thought people were more interested in this. Like, I remember wanting to know this number as precisely as possible when I was a kid. I was really curious about this. And so I was a little surprised that people were just sort of knew it was super old and were satisfied and didn't really care about the details. Although I'll say every single person here after I asked them the question, then they did turn around and ask me. They're like, well, how old is the earth?

So they wanted to know. I guess they just hadn't really spent any time looking it up. All right. Well, let's get started on this topic, Daniel. And so, first of all, I think I feel like we should define what we mean by the Earth, by the age of the Earth, right? Like, do you mean like the planet, like the ball that it's Earth or the rocks in the Earth or the atoms that make up the Earth? What do you mean? Like, what's the age of the Earth?

Yeah, it turns out that that's a bit of a fuzzy question, right? Because the Earth has a sort of continuous history. It's not like somebody snapped their fingers and boom, there was the Earth. and you can start the clock from then, right? That you know of, right? That we know of, that's right. Unless, of course, it was a simulation, in which case, the answer is easy.

But in the case that it was in the simulation, we have an idea about how the Earth was formed, and there's just a lot of stages there. And so you have to sort of make an arbitrary definition. And it's like a lot of things in science. You know, there's not necessarily a clear answer, so you just define it to be something arbitrary, and then at least we can agree on it.

But maybe we should recap sort of the brief history of the earth and how it was formed. Yeah, like how it came to be. And then at some point, we're going to say, this is when the earth started. This is when the earth was born. That's right. This is when the party began, right?

Because, you know, you invite people to a party at 9 o'clock, and then they don't show up until 10, and by then you've eaten all the brownies. And parties only really get started at 1 a.m. That's right. Unless you're in Spain, in which case, it's 4 a.m. But, you know, the very early history is that we basically started with a huge nebula of gas and dust.

This is stuff that's left over from the explosions of other stars and just gas from the Big Bang. And then, of course, gravity did its thing and it pulls all that stuff together and you get a sun, right? So most of the stuff went to the sun. And then you get a disk of stuff that's rotating around the sun. It's like rings around the sun. And then the gravity pulls the stuff in that disk together

to turn that disk into planets, right? And so we think that the solar system started about 4.5 billion years ago and it took like a few million or a hundred million years to pull all that stuff in the disk together into sort of proto-planets, right? So you have this sort of loose collection of stuff that gravity's pulled together and then gravity really gets to work

and it starts squeezing it and it collects all this stuff and the planet heats up and sort of melts the metal and you get the iron dropping to the core and the crust forming. And so you can sort of ask like, At what moment do you count the earth forming? Is it like when you had the first big cluster of rocks or maybe when it got gravitationally heated enough

to sort of melt the metals and form the core? It's not really very clear. Well, I always found this really fascinating because we talked about this the other day that something like the rings around Saturn are only temporary, right? Like at some point, those rings might turn into little blobs. That's right.

Gravity is very weak, but very, very, very. very patient. And so it just keeps working. And you give it enough time. It will gather things together. And so the stuff that's orbiting Saturn, eventually gravity will pull it together into moons. Even the asteroid belt, is that at some point going to turn into more planets for our solar system? Yeah. Eventually, gravity, I mean, it's very slow and those things are mostly stable orbits. But eventually, that stuff will get pulled together. I mean, also there's disruption, right? If you just left the solar system all by itself, then yes, eventually it will just gather together into a smaller and smaller number of objects.

But there's disruption from stuff that comes outside, you know, in comets, things from the Urt cloud, even things like supernovas from other solar system can disrupt things happening in our solar system. So, but yes, eventually gravity will pull all this stuff together. It's really incredible what over these timescales, what gravity can do. And that's one of my favorite things. It's just realizing that these processes are really slow. So things must have been around for a super long.

time to make it happen, right? Right. Well, I guess I would maybe count that the birth of the Earth is when it was form. You know, when all those asteroids and rocks out there clumped together into a ball about the size of the ball that we have now.

Like, you know, when it kind of snapped into shape, I would maybe count that as the age of, when the Earth started. Yeah, yeah, and that's totally reasonable. That's totally reasonable. I think one common definition is that you measure the age of the Earth is sort of the age of the oldest rock in the earth.

And then you can ask the question, well, what does it mean for a rock to be old? Like, you know, a rock is just a gravitationally pulled together clump of dust. But rocks are formed, right? They're melt and then they're cooled. And so the age of a rock is usually like the last time it was melted, right? So it's the time since it was last melted. And so a lot of people just like... Or the time that it cooled off?

The last time it really chilled out. And so you can imagine, like, all these rocks can't. together, as you said, and formed the earth, and got squeezed together and probably melted and then cooled, right? The crust at least cooled. And so you can ask, like, maybe that last moment, the last moment of cooling of the crust, sort of the age of the oldest cooled rock on the earth could be a definition of the age of the earth. Because otherwise, how do you know when these rocks came together, right? Otherwise... I don't know. Unless you have, like, you know, CCTV of the formation of the solar system, it's pretty hard to pin that down. Or you could say... Is it? Well, but you just gave me a number. You said that it was maybe it took around 100 million years to form that, the ball of the Earth. Yeah, that's, I said between a few and 100 million years, right? So that's a pretty big uncertainty.

We don't really know how long it took. And what moment do you define? Like, do you need one more rock? Because, you know, stuff kept getting added to the Earth. And so some people say, well, the age of the Earth is sort of just, let's just call it the age of the solar system. because that's pretty close to the age of the earth or you could say it's the age of the oldest rock on the earth

so I think both of those are sort of acceptable and anyway that's really all we can probe in the end what we do is we measure the age of the oldest rock we can find on the earth and we say that's pretty close to the age of the earth so the time that it formed into a ball is kind of in between those two numbers right yeah exactly like it's between when the solar system

formed and when the ball that is the earth started getting Krusty. Exactly. Exactly. When it started getting crusty and grumpy and eating desserts at parties and going home early. Like a teenager. So somewhere between conception and teenage years, that's when you're born.

That's right. And, you know, we have the same question about people, right? I wonder about that sometimes. You know, how do you count somebody's age? If somebody's born premature, they're older, you know, even than somebody who was born, it was conceived at the same moment, but then born at full term. So even the age of people is sort of hard to define sometimes. All right.

Well, we've determined what we mean by the age of the Earth. And so now let's get into how we know how old the Earth is and what that means. But first, let's take a quick break. December 29th, 1975, LaGuardia Airport. The holiday rush. Parents hauling luggage. kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed.

There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal, glass. The injured were being loaded into ambulances. Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order. criminal justice system is back.

In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly and now I'm seriously suspicious. Well, wait a minute, Sam. Maybe her boyfriend's just looking for extra. credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't

think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor, and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor

or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. Your entire identity has been fabricated. Your beloved brother goes missing without a trace. You discover the depths of your mother's

illness, the way it has echoed and reverberated throughout your life, impacting your very legacy. Hi, I'm Danny Shapese. hero. And these are just a few of the profound and powerful stories I'll be mining on our 12th season of Family Secrets. With over 37 million downloads, we continue to be moved and inspired by our guests and their courageously told stories. I can't wait to share 10 powerful new episodes with you, stories of tangled up identities, concealed truths, and the way in which

family secrets almost always need to be told. I hope you'll join me and my extraordinary guests for this new season of Family Secrets. Listen to Family Secrets Season 12 on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Okay, so we're defining the age of the earth is how old, the oldest, rock was formed that we know about, right, on Earth. That's right, exactly. Let's say... So when the Earth was like a ball of lava, that doesn't count.

But once it started solidifying, then we're saying that's when the Earth was born. Yeah, exactly. Because we're imagining that, yeah, we're imagining that the formation of the Earth probably melted a lot of the rocks because there was this early lava period, as you mentioned. And so as it cooled down and formed the crust, then it made rocks. And it turns out we can figure out how old a rock is. And so that's really our best handle in figuring out how old the earth is. And in the end, it's a lower bound, right?

We say, well, here's an super old rock on the earth. So the earth must be at least that old. Because like we've talked about, like you mentioned, like trying to figure out how old earth is, the only thing we can do is sort of look around and see how old the things in it are. And like what's the oldest thing in it? We know it has to be at least that old. Yeah, yeah, exactly. That's about all we can do.

And, you know, what you can do otherwise to sort of form a theory, you say, I have a concept for how this might have worked, and then you can fit data to it and say, well, I expect, you know, to see these sort of rocks in that case, and you can use that theory to sort of extrapolate a little bit past the data you observe, but that's very, but that's speculative, right? It's based on your concept for how things happen. So the hardest number, the one that you know best, is the oldest thing that you can find. and the oldest thing we find are rocks and so what we do is we try to

turn one question into another question the question we can answer is what's the age of the oldest rock on the earth wouldn't that tell us like if we found a really old rock what if that rock came from before the earth was formed do you know what I mean? Yeah yeah there are some of those actually

like meteorites right meteorites tell us the age of the solar system because we think meteorites were formed in the beginning of the solar system right The first stage is gathered together gas and dust into rocks, right? And so those rocks from space tell us the age of the solar system. But we can tell which rocks came from space and which rocks are from Earth. And so we can distinguish those two.

How can we tell? Oh, well, they're clearly labeled. You asked them. They have a return address, right? It says somewhere near Neptune. It's actually quite interesting. So the distribution of metals in these rocks is very difficult. different for meteorites than it is for rocks on the Earth.

Oh, I see. It's like a different group of rocks. Yeah, it's like they have more nickel in them or they have this other rare stuff. And that's a whole other fascinating field. And also, so these rocks are different from Earth and they tell us like what else is out there in the solar system. And what was out there when the solar system was formed? They're like little time capsules from the very beginning of the solar system. And they actually tell us another interesting story.

So those rocks, we can tell how old they are and they tell us how old the solar system is. So we can answer two questions. We can find a bunch of rocks. We can say, oh, these came from somewhere in the solar system. They're X, Y, Z old. These rocks are here on Earth. They're only, you know, ABC old. All right.

So it all comes down to the question of how do you tell how old the rock is. Yeah, right, exactly. Or a meteorite, which is the same. Which is the same because a meteorite is just basically a rock from space that landed on Earth. And the way we do it is something called radiometric dating, which is not the same as carbon dating, right? which is not the same as online dating either it turns out to be actually kind of similar there's a lot of swiping there's a lot of lying about your age as well

no carbon dating and radiometric dating have similar principles and we should have a whole podcast episode about how carbon dating works carbon dating relates to organic stuff like living beings radiometric dating relates to how old rocks are okay so you find a rock and you're you're staring at it and you're like I wonder when this rock became a rock. Yeah, exactly. When this turned from lava to this heavy thing that I'm holding.

And so we can actually tell, right? We can look at the stuff in it and tell how old when it was formed. How many millions of years ago it cooled. Exactly. And I have so much respect for scientists who develop these techniques. You know, they look at a rock and they say, I want to know how old this rock is. How could I tell? Can I find something inside the rock that I can use as a clock,

something which changes reliably and steadily every year so that I can count it and project back and figure out when that clock started or something. And this is hard to do. You have to find something which is steady and reliable and can be calibrated. It's not trivial, right? You can't just say, oh, I'm just going to measure XYZ property.

You have to invent these techniques, and it takes time and sweat and tears. And so I have so much respect for folks who did this. And in the case of rocks, turns out to be very dependent on the special kind of mineral called zircon. Zircon, like the fig diamond? Like cubic zirconium? Yeah, it's related, exactly, zirconium.

And zircon is a special kind of mineral, and it's special because it has two properties. One, it likes, it's a crystal, and it likes to absorb uranium into it, right? It gobbles up uranium. So when the rock forms, if it has some zircon in it, then it'll grab any uranium that's around it. And the second important property. But wait, what is Zircon made out of? Is it, what is it like a meat out of iron or what is it, or carbon? What is this mineral made out of?

I think it's made out of leftover desserts. No, it's made out of bananas. It's a mineral. It's made out of zirconium and silicon and oxygen. Oh, so serconium is like an element, like carbon or iron. Yes, zirconium is an element. And it's sort of like a silver metal. It's atomic number 40.

It doesn't really play a lot of roles in stuff other than cubic zirconium. It's not like a famous metal like some of its friends and neighbors. But it plays an important role in aging rocks. So this element is all around us and it's in all the rocks and it forms a special crystal you're saying that when it forms, it likes to capture uranium.

That's right. It captures uranium and it rejects lead. So the moment that the rock is created, it creates a special thing, which is Zircon, with just uranium in it. And you might wonder, like, well, how is that helpful, right? Well, uranium, as you might know, is radioactive. It doesn't just sit around and stay uranium forever. It very reliably decays, and it decays into lead.

But wait, why does Zirgon like uranium and why doesn't it... You mean, like, when it forms the crystals, it forms a little structure, and it just likes uranium? like uranium likes being inside of zircon crystals i mean i don't want to get in the mind of uranium or the mind of zircon i mean they they did some carbon dating online and they decided they were a good match um but no no some chemical some business with the chemical bonds you know the way the crystal structure of zircon forms fits very nicely with uranium and doesn't fit very nicely with lead right i see yeah so like a rock i have a bunch of lava and it cools and it slowly turns into rock

And in that process, is when you're saying this crystal form. Yeah, and zircon, it doesn't have to be all over the rock. It's not like a whole rock full of zircon. It's just these little chips of zircon. And what they do is they repel all the lead inside them, and they grab some uranium. And their uranium is like a clock. It decays very reliably. So every million years or so, some uranium turns into lead.

And so after one million years, some fraction of the uranium, and then zircon has turned into lead. After 2 million years, another fraction has turned into lead. After a billion years, a very predictable fraction has turned into lead. So what you do is you take a rock, you look at that you find some zircon crystals, and you ask how much of the uranium has turned into lead. And that tells you how much time it's had to turn into lead. It's kind of like an aging process, right? Like wine.

If you leave wine there, it's going to change its characteristic. Exactly. It's going to change into something else. Exactly. And you need, that's why it works so well as a clock, because uranium is something that we know reliably. We understand it. We know how it decays. We know how long it takes. We know, you know, after 100,000 years, what fraction of uranium atoms will turn into lead. And the other key thing, of course, is that it starts with a blank slate. That when you form these zircon crystals, it rejects lead, right? So you start out like with an empty bucket. And then slowly the uranium bucket fills the lead bucket. And so you can just measure the uranium lead fraction. And that tells you, how long the uranium has been turning into lead. It's really amazing. It's really just chance that this happens and that somebody figured this out. So, like, if you find a rock and you find a little zircon chip inside of it,

and it's like, let's say it's full of uranium, then you know it's a pretty new rock. Exactly. But if it's full of lead, then you know it's a really old rock. Exactly. It's exactly right. So rocks start out pure uranium, no lead. And then as they age, the uranium turns into lead. And so a rock with almost no uranium in it is going to be like super duper old, right?

And new lead can't just like come in from the outside because now it's crystallized, right? It's hard for lead to get in any other way. Oh, the only way you can get lead inside the zircon is for uranium to turn into lead. So the rock sort of, you might say like it spoils or ages. By looking at that, yeah, like it turns into lead, right? Yeah, exactly. And whether it spoils or ages beautifully depends on, you know, preference for how rocks taste, I suppose.

Whether you swipe right or left for rocks. That's right. But, you know, it took a long time to figure this out. People tried all sorts of other strategies first before they discovered this one. And there was lots of scientific careers and PhD PCs that were frustrated in people trying to figure out a way to do radiometric dating before people stumbled onto this one. Wow. And this is not one of these things that you have to calibrate, right? because I imagine you have probably very scientific information about the decay of uranium, right? Like it's very physics-based.

Like you don't have to calibrate it to anything else, do you? You're right. We can basically use simple physics arguments to argue how long uranium takes to decay into lead. And so it gives us pretty clear descriptions. But, you know, we also want to get confidence in it. And so what people do is they have various other sort of radiometric methods, not just uranium to lead, but other stuff. Things that decay faster, things that decay slower. And so you can use those to sort of cross-calibrate.

But uranium to lead is the cleanest one. But, you know, like everywhere in science, you want to check everything three different ways and then make sure you get consistent answers. All right. That's pretty cool. That's how we can tell how old rock is then. Rock can't lie. I can't lie about its age. That's right.

That's right. You can lie, but we'll know you are. All right, let's get into the answer now, Daniel, how old Earth is and how old the solar system is. But first, let's take another quick break. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal glass.

The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and order, criminal justice system is, Back. In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Well, wait a minute, Sam, maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school. week on the OK Storytime podcast, so we'll find out soon.

This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor, and they're the same age. It's even more likely that they're cheating.

He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. Your entire identity has been fabricated. Your beloved brother goes missing without a trace. You discover the depths of your mother's illness, the way it has echoed and reverberated throughout your life, impacting your

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All right, Daniel, let's break it down for people. How old is the earth? Or at least the oldest rocks on Earth. Yeah. The oldest rocks on Earth come from. Australia. And I don't know why, but that's not surprising to me. It seems like Australia is the land of extremes. And so you'd expect the craziest, weirdest, oldest rock to be in Australia. They have the biggest spiders, the biggest crocodiles, and the oldest rocks. The deadliest everything.

The biggest movie stars, it seems. And the best podcast listening fans, right? No, we got a lot of good email questions from Australia. But the oldest rock on Earth come from the Jack Hills of Australia And it's 4.04 billion years old. So these are rocks that we, did we have to dig up for them, dig for them? Or are they, were they pretty close to the surface? Yeah, it's fascinating. Actually, these rocks just sort of sit on outcrops. And people recently discovered that they have, that the oldest rocks are there.

And, you know, it's the Earth itself, of course, has had lots of geologic activity. And so some of these really old rocks get buried. And then there's geologic activity that brings them up to the surface. And so it just happens to be at this spot on the earth, these really old rocks got pushed up. And so they're not that far underground. They're on this outcropping of rocks in Western Australia. But you almost kind of expect them to be close to the surface, right? Because that's, you know, I would imagine that if we were once a ball of lava,

then the stuff sort of cools from the outside inwards. That's true. But, you know, then there's all these sedimentary processes where old things get buried. But then there's tectonic activity and all sorts of other crazy stuff that brings stuff up and mixes everything around. So there's a lot of stuff going on there. I think it's not that simple. But in the end, the oldest thing we found on Earth

is almost four and a half billion years old. It's 4,404 million years old. And, you know, that's a staggering answer. It's hard to really comprehend what that means. Four billion years old. That's a lot. It's a lot of dessert parties, yeah. I mean, if the history...

That's a lot of party missed. Yeah. Yeah, I think what you said earlier about how we came to the party pretty late, it's sort of shocking. You know, the first people to, like, learn these numbers to know that the Earth was billions of years old. It must have made humans feel sort of small and recent and, you know, maybe transient, right? Like, the Earth has had a long history, and we are only the very last little bit of it. Yeah, I mean, it's a difference between, I mean, human history is maybe, what, like 10,000, 20,000 years old? Yeah, 100,000 if you're really generous.

Yeah. but the Earth has been around for 4.4 billion years old. Yeah, exactly. It's not too impressed. It's been there. It's seen a lot of stuff. You know, it'll be here when we're done. You know, people always talk about how humans are going to destroy the Earth.

And I don't think that's likely. I think the humans might destroy ourselves or life on Earth, but the Earth will be here when we're done. Unless I hear some physicists are trying to make black holes down at the Large Hadron Collider. Yeah, but we just want to understand the universe, man. We're not threatening the world. There's no danger there. Trust me.

And can I have $10 more billion to build a bigger one? One dollar for every year that the Earth has been alive. That's right. That sounds good. But, you know, that's the oldest rock on Earth that we think is part of the Earth. It was part of the formation of the Earth. But, of course, we have found rocks on Earth that are meteorites, right, that came from space, that are older than the Earth itself.

So late comers to the party. That's right. They heard there was something cool happening. down here in the third rock from the sun and they fell on in to figure it out. And those rocks are 4.56 billion years old. So that's like 150 million years older than the oldest rocks on Earth. That's the oldest meteorite that we found. And I think that you were saying that that kind of tells us what the oldest meteorite at all is in our solar system, right?

Yeah, using the same logic, this is the oldest thing we found. Yeah. So it's probably the sort of the age of the solar system, right? That's when we think the gas and the dust got accumulated together to form the sun and the planets and all that stuff. But the first stage of that was to form smaller rocks. And so we think these things are remnants of those times. Right. But wait, didn't the sun, hasn't the sun, our sun, already been through a couple of cycles?

Like, hasn't exploded a few times already? Well, our sun hasn't exploded, but its materials, right, have been through several solar cycles. Everything around us, all that stuff is left over from one or two or three solar cycles. cycles of a sun lasting for, you know, one, two, three billion years and then blowing up and spreading its materials around. So everything around us is all the components of the solar system are probably been recycled. But it's not like our sun formed and then restarted and formed and restarted. It was from a different star. Oh, I see. So our current sun is maybe around 4.5 billion years old. Yeah, that's what we think. That's the history of our solar system. And remember

for context, the Milky Way is something like 13 billion years old, and the universe is just a little bit older than that, almost 14 billion years old. So there's a lot of history before even our sun, our solar system was formed, and then a lot of history before we came around. And so, like, that's the cosmic context that we're standing in. And so that's the oldest thing we found in the solar system, but that's older than the oldest thing we found that is part of the Earth. So somewhere between those two numbers is when maybe the ball of the earth forms. That's right. That's what we call the Jorge date.

The Jorge definition of the age of the earth. The ball date. Jorge's ball date. That's right. That's right. And so, you know, there's a window there about 150 million years, which seems like a huge number, you know, that's like 150 million years.

No, but it's pretty small, I think, compared to... Geologically speaking, it's a blink of an eye. Yeah. Or universe speaking, it's pretty accurate. Yeah, exactly. And, you know, we know these numbers two plus or minus 25 or 50 million years based on the uncertainty of radiometric dating. And so because of the hard work of a lot of scientists to develop these things

and to cross-check them and understand them across various other processes, now we've looked around us and we've gathered these clues from everyday objects around us. You know, the rocks at our feet, the rocks in Australia, give us clues about these fantastic numbers that would just blow the minds of our ancestors and those clues were around for them to discover also. And so, of course, that makes you wonder, like, what clues are there laying around at our feet now

that would tell us secrets of the universe that our descendants will know and wonder why we couldn't figure it out? It's not just like an opinion, right? It's pretty based on evidence and it's pretty based on science and physics, these numbers. Yeah, exactly. These things we know pretty well. We have a lot of confidence in them.

People have been working on these processes for decades and decades. A lot of, you know, grumpy competition between rivals to make more and more accurate measurements. You know, this is not a conspiracy of scientists all working together in harmony. You know, this is a bunch of people racing to develop better and better techniques and trying to find older and older rocks. Remember, science is a competitive field and everybody wants to one up the other to get the more accurate, the more reliable, the more verifiable answer. So yeah, we have a lot of confidence in this knowledge. Yeah, it's like it's all around. The evidence is all around us and you're standing on it.

Yeah, exactly. And even if you can't do radiometric dating in your head, of course, because you can't see the zircon crystals, you know, you just look around you and you see lots of things around you which take a long time to form, you know? How long does it take a mountain to form? It's a very slow process. And so all around us on the earth, we see evidence of very, very slow processes which have accomplished a great deal, which tells you, that they've been doing it for a long, long time. Yeah. Like you said, who knows what else is lying under our feet?

That's right. Exactly. So, I think we answered that question about the age of the earth. Yeah. Yeah. So grab a glass of wine and sit back and enjoy it. That's right. And no matter how old you are, remember, you can always enjoy one more brownie.

See you next time. Thanks for tuning in. And thanks for asking great questions. This question was inspired by an email from me. listener. So if you have a question you'd like to know the answer to, please send it to us at questions at danielanhorpe.com. If you still have a question after listening to all these explanations, please drop us a line. We'd love to hear from you. You can find us at Facebook, Twitter, and Instagram at Daniel

and Jorge, that's one word, or email us at Feedback at Daniel and Jorge. Thanks for listening and remember that Daniel and Jorge Explain the Universe is a production of IHeartRadio. For more podcasts from IHeartRadio, visit the IHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. Ah, come on, why is this taking so long? This thing is ancient. Still using yesterday's tech?

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so you can work, create, and boost productivity all on one device. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, everything changed. There's been a bombing at the TWA terminal, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, terrorism. Listen to the new season of Law and Order Criminal justice system on the iHeart radio app apple podcasts or wherever you get your podcasts my boyfriend's

professor is way too friendly and now i'm seriously suspicious wait a minute sam maybe her boyfriend's just looking for extra credit well dakota luckily it's back to school week on the okay story time podcast so we'll find out soon this person writes my boyfriend's been hanging out with his young professor a lot he doesn't think it's a problem but i don't trust her now he's insisting we get to know each other but i just Swann or gone. Oh, hold up. Isn't that against school policy? That seems inappropriate.

Maybe find out how it ends by listening to the OK Storytime podcast and the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. This is an IHeart podcast.