WEBVTT - How old is the earth? 0:00:08.160 --> 0:00:11.000 Hey, Daniel, do you keep a family photo album? You know, 0:00:11.119 --> 0:00:13.880 we used to, but these days it's all digital. I 0:00:13.880 --> 0:00:17.360 think Mark Zuckerberg owns all of our family photos. It 0:00:17.440 --> 0:00:20.960 owns your family period. Probably that too. But and how 0:00:20.960 --> 0:00:23.040 do you feel when you look back and see pictures 0:00:23.120 --> 0:00:25.599 of yourself when you were younger? Um? I try to 0:00:25.640 --> 0:00:28.040 ignore all those signs of aging, you know, pretend that 0:00:28.040 --> 0:00:29.920 I looked the same ten or twenty years ago as 0:00:29.960 --> 0:00:32.960 I do today. I see myself as a fine wine 0:00:34.159 --> 0:00:37.960 because you have turned, because I just get more expensive 0:00:38.000 --> 0:00:40.600 the older I get. For some reason. Well, you know, 0:00:40.640 --> 0:00:43.720 I've known you for over ten years or so, and 0:00:44.040 --> 0:00:46.560 I can I can say with confidence for those people 0:00:46.560 --> 0:00:49.680 listening that you are so or no Paul Rudd. Unfortunately 0:00:50.680 --> 0:00:53.720 that's true in many ways, unfortunately. But it is kind 0:00:53.760 --> 0:00:57.440 of interesting how little clues can show you how old 0:00:57.520 --> 0:01:00.560 someone is or how old something is. Right, It's true, 0:01:00.600 --> 0:01:03.040 you know, a few wrinkles here and a few gray 0:01:03.080 --> 0:01:05.600 hairs there, and all of a sudden, you look like 0:01:05.640 --> 0:01:09.840 you're in your midlife crisis. What's that look like a 0:01:09.880 --> 0:01:13.720 look of panic? It's a look of gravitas. I always 0:01:13.760 --> 0:01:17.320 remember how dan Quail died his temples gray and which 0:01:17.400 --> 0:01:20.080 not look so much like a little boy Dan quail Man. 0:01:20.160 --> 0:01:23.520 That's a that's a reference that totally tells everyone how 0:01:23.560 --> 0:01:29.320 old you are. Nobody's fascinating how almost everything around us 0:01:29.480 --> 0:01:33.360 ages right. Everything from people around you, to the rocks 0:01:33.400 --> 0:01:36.959 around you, um to the buildings around you always show 0:01:37.040 --> 0:01:40.000 their signs of age. Nothing in this world is permanent. 0:01:56.200 --> 0:02:00.280 Hi am poor handmade cartoonists and the creator of PhD comics. Hi. 0:02:00.480 --> 0:02:05.000 I'm Daniel. I'm a particle physicist, and I'm young and spry, 0:02:05.040 --> 0:02:07.560 and I have not written any web comics, but I'm 0:02:07.560 --> 0:02:10.600 the co author of the book We Have No Idea 0:02:10.800 --> 0:02:14.240 All about the unknown Questions in the Universe. And welcome 0:02:14.280 --> 0:02:17.560 to our podcast, Daniel and Jorge Explain the Universe, a 0:02:17.680 --> 0:02:20.720 production of I Heart Radio, in which we take weird 0:02:20.800 --> 0:02:23.760 and amazing and young and old stuff in the universe 0:02:23.800 --> 0:02:26.400 and try to explain it to you, and not just 0:02:26.520 --> 0:02:29.360 telling you the answers, but sometimes digging in deeply and 0:02:29.400 --> 0:02:32.080 explaining how we know so that you can explain it 0:02:32.320 --> 0:02:35.639 to skeptical folks around you. Yeah, we try to get 0:02:35.639 --> 0:02:38.840 you to think about the world around you and even 0:02:38.880 --> 0:02:41.960 the world you're standing on right now or sitting on 0:02:42.080 --> 0:02:45.600 or lying down on and one of the depending depending 0:02:45.600 --> 0:02:48.320 on how old you are. But one of the goals 0:02:48.320 --> 0:02:50.400 of this podcast is for you to have sort of 0:02:50.400 --> 0:02:53.080 a new perspective on the world around you. We want 0:02:53.080 --> 0:02:55.799 you to see everything around you as sort of a clue, 0:02:56.200 --> 0:02:58.480 something that can tell you how the world works, that 0:02:58.560 --> 0:03:02.600 can reveal secrets. I can answer questions because almost every 0:03:02.680 --> 0:03:05.639 question we have about the universe, the answers are all 0:03:05.639 --> 0:03:08.079 around us, and it just takes sort of a trained 0:03:08.160 --> 0:03:11.320 mind and a careful eye to see those clues everywhere. 0:03:11.400 --> 0:03:14.280 And so there are clues all around you about where 0:03:14.320 --> 0:03:16.720 we come from and how long we've been here, and 0:03:16.760 --> 0:03:19.960 how long everything has been here? Right, Yeah, exactly. And 0:03:20.320 --> 0:03:23.480 sometimes answers are easy and obvious, and sometimes the answers 0:03:23.520 --> 0:03:27.200 are mind mogglingly surprising. And so today on the podcast, 0:03:27.200 --> 0:03:31.120 we'll be tackling, quite possibly the oldest question on earth. 0:03:31.160 --> 0:03:33.200 Would you say that's true, Daniel, is that who stole 0:03:33.240 --> 0:03:35.800 my dessert? Um? I think the answer is obvious, obviously, 0:03:35.800 --> 0:03:39.040 it's your your children. Well you know, Um, that's actually 0:03:39.080 --> 0:03:42.440 a question my kids asked me today. Um, when was 0:03:42.480 --> 0:03:46.320 dessert invented? It sounds like a topic for a pope, 0:03:46.720 --> 0:03:49.080 you know, if that falls into a physics question. But 0:03:49.080 --> 0:03:51.800 it's sort of a fascinating question, and they were actually 0:03:51.880 --> 0:03:55.400 hypothesizing that dessert might be older than people that maybe, 0:03:55.520 --> 0:04:00.240 like our prehuman ancestors, enjoyed a sweet, sweet treat after dinner. 0:04:00.440 --> 0:04:03.000 What do you think the little bacteria the good that 0:04:03.280 --> 0:04:06.280 well the ocean? They're like, you know, I could use 0:04:06.320 --> 0:04:10.840 a little two remy suit after consuming the other other bacteria. 0:04:11.040 --> 0:04:12.840 I don't know if we have enough in common with 0:04:12.920 --> 0:04:15.080 bacteria to say what they might like, but I can 0:04:15.160 --> 0:04:18.960 imagine it's some pre human homaid, you know, eating some 0:04:19.040 --> 0:04:22.000 berries and going and that goes nicely with my antelope 0:04:22.080 --> 0:04:24.760 or whatever they had for dinner. Well anyway, so so weely. Uh. 0:04:24.920 --> 0:04:28.080 What I mean by it's the oldest question on Earth 0:04:28.279 --> 0:04:31.560 is that it's it's probably really the oldest question that 0:04:31.600 --> 0:04:33.839 could be on Earth, right, Yeah, I think that's probably true, 0:04:34.200 --> 0:04:36.640 And it's a it's an important question, right. It's the 0:04:36.760 --> 0:04:39.080 kind of question that we'd like to dig into because 0:04:39.480 --> 0:04:42.800 it's the kind of question where the answer could change 0:04:42.839 --> 0:04:45.719 the way we think about life and the universe and 0:04:45.800 --> 0:04:48.400 the humanity's rolling it right, it has all sorts of 0:04:48.440 --> 0:04:51.320 things to do with with creation and the context of 0:04:51.360 --> 0:04:53.960 our lives and therefore how we should live our lives 0:04:53.960 --> 0:04:55.640 and whether they have meanings and so to be. On 0:04:55.640 --> 0:05:04.040 the podcast, we'll be tackling the question how old is 0:05:04.080 --> 0:05:08.520 the Earth? And is it even polite to ask? That's right? 0:05:09.080 --> 0:05:11.200 And what does the earth do when he gets upset? 0:05:11.440 --> 0:05:14.520 All right, when he gets offended? Um? And not just 0:05:14.600 --> 0:05:16.400 how old had any worked? One? Has the Earth had 0:05:16.440 --> 0:05:20.080 any work? One? Is it trying to? I think the 0:05:20.120 --> 0:05:25.040 Earth looks great. Doesn't look a day past four billion? Um? 0:05:25.040 --> 0:05:29.000 It is full of buetos. They're probably right, um. And 0:05:29.400 --> 0:05:31.560 just as important as the question how old is the 0:05:31.560 --> 0:05:33.800 Earth and the answer, which is you know, just a number, 0:05:34.240 --> 0:05:36.720 is how do we know? How do we have confidence 0:05:36.760 --> 0:05:38.800 in this answer? Because you know, there are people out 0:05:38.800 --> 0:05:41.360 there who hold beliefs about the various age of the Earth. 0:05:41.680 --> 0:05:44.279 And one of our listeners actually wrote in and said, hey, 0:05:44.320 --> 0:05:46.520 could you tell me how we know the age of 0:05:46.560 --> 0:05:48.680 the Earth, so that when I discussed with my friends 0:05:48.720 --> 0:05:51.040 who have strong opinions about the age of the Earth, 0:05:51.200 --> 0:05:54.039 I can tell them not just what scientists think, but 0:05:54.200 --> 0:05:56.200 how they know it. Yeah, And that's the thing I 0:05:56.240 --> 0:05:58.200 think we always try to do in this podcast, right, 0:05:58.279 --> 0:06:00.679 is try to get at how people know these things, 0:06:00.680 --> 0:06:04.200 not just tell people what scientists know, but how they 0:06:04.240 --> 0:06:06.479 know it. That's right, And that also helps you understand 0:06:06.839 --> 0:06:09.159 with what confidence we know it, Like is this just 0:06:09.240 --> 0:06:11.679 sort of an educated guess the back of the envelope 0:06:11.680 --> 0:06:14.160 calculation or is this something that people have been working 0:06:14.200 --> 0:06:16.800 on for hundreds of years and we have great confidence 0:06:16.839 --> 0:06:19.480 and have it nailed down to like point oh one percent. 0:06:19.800 --> 0:06:22.640 And it's important because different things in science are are 0:06:22.680 --> 0:06:25.520 known well and some things since science are are known 0:06:25.560 --> 0:06:28.800 not very well. So it's important to know how we know. Yeah, 0:06:28.880 --> 0:06:31.320 And so how old is the Earth is the question 0:06:31.320 --> 0:06:34.600 for today, and it's kind of um, I think it's 0:06:34.600 --> 0:06:37.960 a question most people know a little bit about, right. 0:06:38.040 --> 0:06:40.520 I mean, I think everyone knows or has a sense 0:06:40.520 --> 0:06:43.400 that the Earth is very old. Yeah, but you know, 0:06:43.920 --> 0:06:47.160 that sense that the Earth is like extremely old, like 0:06:47.760 --> 0:06:50.719 many orders of magnitude older than you or me or 0:06:50.760 --> 0:06:55.040 your parents, you know, is a fairly modern idea. I 0:06:55.080 --> 0:06:58.359 think thousands of years ago people thought the Earth was 0:06:58.600 --> 0:07:01.359 only hundreds or thousands of years old. They thought it 0:07:01.440 --> 0:07:04.239 might have been created fairly recently, and it was only 0:07:04.279 --> 0:07:06.680 sort of in the eighteen hundreds that people started to 0:07:06.760 --> 0:07:10.160 understand that there were processes around us that we could see, 0:07:10.400 --> 0:07:15.080 specifically rocks and evolutions or geology and biology started to 0:07:15.120 --> 0:07:18.640 give hints that the answer was much much bigger than 0:07:18.680 --> 0:07:22.480 anything anybody had imagined. And I think that's wonderful. I 0:07:22.480 --> 0:07:24.760 I love to live in a scientific era like that, 0:07:24.800 --> 0:07:29.080 where you're where something you thought you knew is upended 0:07:29.120 --> 0:07:31.760 and replaced with a completely different answer. That's like oors 0:07:31.760 --> 0:07:36.160 a magnitude bigger. Wow, is that really true? Like it 0:07:36.360 --> 0:07:39.160 only in the last couple of hundred years do we 0:07:39.360 --> 0:07:41.760 have a sense of how old the Earth really is? 0:07:42.160 --> 0:07:44.000 Before it was totally up in the air. Yeah, it 0:07:44.000 --> 0:07:45.760 was up in the air until about the eighteen hundreds, 0:07:45.760 --> 0:07:48.520 and then people started trying to do calculations and they're like, well, 0:07:48.840 --> 0:07:51.160 how long would it take to form a planet, you know, 0:07:51.240 --> 0:07:53.920 so you gathered it together with gravity, or you know, 0:07:54.520 --> 0:07:57.120 how how long would it take to lay down layers 0:07:57.160 --> 0:07:59.720 of rock? You know, how long would it take glaciers 0:07:59.720 --> 0:08:02.600 to this kind of stuff? And you know, geology is 0:08:02.600 --> 0:08:04.400 a fairly young field and that you know, it's a 0:08:04.440 --> 0:08:06.800 couple of hundred years old and so people started to 0:08:06.840 --> 0:08:09.440 look around, and as soon as they started to explore 0:08:09.840 --> 0:08:13.680 these geological processes, they realized, wow, this stuff takes a 0:08:13.720 --> 0:08:17.360 long time. And you know, it's sort of like um 0:08:17.440 --> 0:08:19.920 walking into a room and seeing somebody has written a 0:08:19.960 --> 0:08:23.800 book that's like five million pages long, and you're like, wow, 0:08:24.040 --> 0:08:26.000 you've been in this room a long time, you know, 0:08:26.200 --> 0:08:29.840 so it shocks you into realizing the things things are 0:08:29.880 --> 0:08:32.880 a much different scale than you imagined. And that's the 0:08:33.080 --> 0:08:35.240 we've seen the story the earth all around us. We 0:08:35.320 --> 0:08:39.680 realize it's staggeringly long, much longer than we imagined, and that, yeah, 0:08:39.679 --> 0:08:41.800 that's a fairly new idea. Yeah, that's a lot of 0:08:41.880 --> 0:08:46.760 party you've missed exactly we should. Things have been around 0:08:46.800 --> 0:08:49.280 for a long time. Do you have a fear of 0:08:49.280 --> 0:08:53.840 missing out? There? Is that fomo about what happened? All 0:08:53.840 --> 0:08:56.920 the good desserts? Fear of being in parties? Actually, to 0:08:57.000 --> 0:08:59.120 be honest, what about all the desserts? The usually have 0:08:59.120 --> 0:09:02.120 good dessertsive party old desserts or I just like I 0:09:02.200 --> 0:09:05.640 just like a fine dessert. Wine? So you should you 0:09:05.640 --> 0:09:07.200 show U at the beginning of the party, how the 0:09:07.240 --> 0:09:09.800 desserts drink the wine and then go home? That's how 0:09:09.840 --> 0:09:11.319 you know you're old or that was like a good 0:09:11.320 --> 0:09:15.359 party to me. That is how your age old track exactly. 0:09:15.760 --> 0:09:20.000 That's very age appropriate. Um. The beginning of this field 0:09:20.040 --> 0:09:22.839 like becoming scientific before that was just speculation of the 0:09:22.880 --> 0:09:26.440 beginning of the field. Becoming scientific was in the eighteen hundreds. Um. 0:09:26.480 --> 0:09:29.280 But still that's very inaccurate. Like looking at rocks gives 0:09:29.280 --> 0:09:32.240 you clues about the sort of order of magnitude, But 0:09:32.280 --> 0:09:34.680 then people wanted to know very precisely, and that took 0:09:35.280 --> 0:09:38.760 that took some time to to like basically defined clocks 0:09:38.800 --> 0:09:41.400 inside the earth, clocks that have been ticking since it 0:09:41.440 --> 0:09:44.440 was born. And that's in the end signs of aging, Yeah, 0:09:44.520 --> 0:09:46.719 signs of aging, very precise signs of aging that could 0:09:46.760 --> 0:09:48.679 tell us how old the earth was. So you're saying, like, 0:09:49.200 --> 0:09:52.520 you know, the people who started the United States, like 0:09:52.559 --> 0:09:56.600 the founding father fathers, like the Founding Fathers, they had 0:09:57.040 --> 0:09:59.959 no idea how old we've been around, Like did they 0:10:00.040 --> 0:10:01.920 think we've been around for a few thousand years? For 0:10:02.000 --> 0:10:05.000 a few but didn't they know about the you know, 0:10:05.520 --> 0:10:08.000 like ancient Egypt and things like that. Yeah, but you 0:10:08.040 --> 0:10:10.360 know that's thousands of years, and so I think they 0:10:10.400 --> 0:10:12.800 had the idea that the Earth was, you know, thousands, 0:10:12.840 --> 0:10:16.360 many thousands of years old, right, because that's as long 0:10:16.400 --> 0:10:18.839 as written history is, and so they imagine it's on 0:10:18.920 --> 0:10:21.160 that time scale because that's the oldest thing, you know. 0:10:21.559 --> 0:10:24.240 And that's basically the game is like find the oldest 0:10:24.240 --> 0:10:27.000 thing you know and then assume that that's basically the 0:10:27.080 --> 0:10:29.920 age of the world, right, And that's frankly what we're 0:10:29.960 --> 0:10:32.360 still doing, um, except that we think that we found 0:10:32.400 --> 0:10:34.480 stuff that comes from the very beginning of the world. 0:10:34.520 --> 0:10:36.960 But you know, they knew about stuff that was thousands 0:10:36.960 --> 0:10:38.800 of years old, so they had no reason to believe 0:10:39.160 --> 0:10:42.680 that the Earth might be millions or even God forbid, 0:10:42.960 --> 0:10:45.680 billions of years old, right. Plus I think those guys 0:10:45.720 --> 0:10:48.000 are pretty religious, all right. So it is an age 0:10:48.000 --> 0:10:50.400 old question and one that a lot of people have 0:10:50.559 --> 0:10:53.400 had answers to and seems seemed to have answers to. 0:10:53.720 --> 0:10:56.120 But we were wondering what people out there right now 0:10:56.400 --> 0:10:59.000 in the world think about this question. Yeah, and this 0:10:59.040 --> 0:11:01.240 is one this is a set of interviews. I was 0:11:01.520 --> 0:11:04.240 very curious to see what people thought. I was wondering 0:11:04.280 --> 0:11:06.240 if I would run into some sort of young Earth 0:11:06.280 --> 0:11:10.679 folks who thought the Earth was from biblical ages and uh, 0:11:10.720 --> 0:11:12.800 and even those people who were scientific. I was wondering, like, 0:11:12.800 --> 0:11:15.080 how precisely do people know the age of the Earth. 0:11:15.160 --> 0:11:17.720 So this I was very fascinating to hear the answers 0:11:17.720 --> 0:11:22.400 like is it a million years, a bazillion years, twenty 0:11:22.480 --> 0:11:25.560 seven point two bazillion? And so, as usual, Daniel went 0:11:25.600 --> 0:11:29.080 out and asked people on the street how old they 0:11:29.160 --> 0:11:31.360 thought the Earth was. So think about it for a second. 0:11:31.440 --> 0:11:34.880 If you ran into a physicist in the street, uh today, 0:11:35.640 --> 0:11:38.840 how would you answer this question? And no googling. Well, 0:11:38.880 --> 0:11:41.400 here's what people had to say. Um, I have no 0:11:41.440 --> 0:11:46.319 idea probably billion years. I don't exactly, but my understanding 0:11:46.400 --> 0:11:49.280 is it's a couple of hundred million years old. Okay, 0:11:49.520 --> 0:11:51.800 you know how we know? So I don't actually like 0:11:51.840 --> 0:11:54.560 my my physics knowledge is pretty limited. Um. I think 0:11:54.600 --> 0:11:58.280 like we've used carbon dating to date things within various 0:11:58.280 --> 0:12:02.120 geological epox but I don't actually know how we arrived 0:12:02.160 --> 0:12:06.880 at the calculation of the Earth stage and maybe three 0:12:06.960 --> 0:12:14.920 billion years, tens of million years, four billion years, and 0:12:14.960 --> 0:12:18.160 how do we know rock formation? It's probably like millions 0:12:18.160 --> 0:12:20.760 of years old. I feel like, all right, Um, a 0:12:20.800 --> 0:12:24.080 lot of millions and billions, right, yeah, exactly, not not 0:12:24.200 --> 0:12:26.160 a whole lot of really specific answers. I have to 0:12:26.160 --> 0:12:28.840 say I was a little bit disappointed. I guess I 0:12:28.880 --> 0:12:31.080 thought people were more interested in this, Like I remember 0:12:31.120 --> 0:12:33.440 wanting to know this number as precisely as possible when 0:12:33.480 --> 0:12:36.120 I was a kid. I was really curious about this, um, 0:12:36.200 --> 0:12:37.760 and so I was a little surprised that people were 0:12:37.840 --> 0:12:40.200 just sort of knew it was super old and were 0:12:40.240 --> 0:12:43.360 satisfied and didn't really care about the details. Although I'll 0:12:43.360 --> 0:12:46.760 say every single person here after I asked them the 0:12:46.880 --> 0:12:49.079 question then they did turn around and ask me. They're like, well, 0:12:49.120 --> 0:12:51.520 how old is the Earth? So they wanted to know 0:12:51.679 --> 0:12:54.559 abous just hadn't really spend any time looking it up. 0:12:54.600 --> 0:12:56.920 All right, Well, let's get started on this topic, Daniel 0:12:56.960 --> 0:12:59.040 and so, um. First of all, I think I feel 0:12:59.080 --> 0:13:01.520 like we should define what we mean by the Earth 0:13:02.040 --> 0:13:04.360 by the age of the Earth, right, Like, um, do 0:13:04.400 --> 0:13:07.560 you mean like the the planet, like the ball that 0:13:07.640 --> 0:13:10.760 it's Earth, or the rocks in the Earth, or the 0:13:10.840 --> 0:13:12.720 atoms that are that make up the Earth? What do 0:13:12.720 --> 0:13:14.760 you mean, like what's the age of the Earth. Yeah, 0:13:14.800 --> 0:13:18.040 it turns out that that's a bit of a fuzzy question, right, 0:13:18.120 --> 0:13:21.760 because the Earth has a sort of continuous history. It's 0:13:21.800 --> 0:13:24.920 not like somebody snapped their fingers and boom, there was 0:13:24.960 --> 0:13:28.319 the Earth. And you can start from the clock from then, right, Um, 0:13:28.360 --> 0:13:31.240 that you know of, right, that we know of, that's right, unless, 0:13:31.280 --> 0:13:33.600 of course it was a simulation, which case things is easy. 0:13:34.080 --> 0:13:36.720 But in the case that it wasn't the simulation, we 0:13:36.760 --> 0:13:39.400 have an idea about how the Earth was formed, and 0:13:39.440 --> 0:13:41.120 there's just a lot of stages there, and so you 0:13:41.160 --> 0:13:44.720 have to sort of make an arbitrary definition and into 0:13:44.800 --> 0:13:47.000 like a lot of things in science, you know, Um, 0:13:47.040 --> 0:13:49.080 there's not necessarily a clear and sower. So you just 0:13:49.120 --> 0:13:51.000 define it to be something arbitrary and at least we 0:13:51.040 --> 0:13:53.760 can agree on it. But maybe we should recap sort 0:13:53.760 --> 0:13:55.880 of the brief history of the of the Earth and 0:13:55.880 --> 0:13:58.360 how it was formed, yeah, like how it how it 0:13:58.440 --> 0:14:00.240 came to be. Yeah, And then at some point we're 0:14:00.240 --> 0:14:02.320 gonna say, this is when the earth started, this is 0:14:02.320 --> 0:14:03.839 when the Earth was born. That's right. This is when 0:14:03.840 --> 0:14:06.720 the party began, right, um, Because you know, you invite 0:14:06.720 --> 0:14:08.880 people to party at nine o'clock and then they don't 0:14:08.880 --> 0:14:10.400 show up till ten, and by then you've eating all 0:14:10.400 --> 0:14:14.640 the brownies, um, and parties only really get started at 0:14:14.640 --> 0:14:17.360 one a m. That's right, unless you're in Spain, in 0:14:17.360 --> 0:14:20.160 which cases four am um. But you know, the very 0:14:20.240 --> 0:14:22.920 early history is that we basically started with a huge 0:14:23.280 --> 0:14:25.560 nebula of gas and dust. And this is stuff that's 0:14:25.640 --> 0:14:28.480 left over from the explosions of other stars and just 0:14:28.520 --> 0:14:31.480 gas from the Big Bang. And then of course gravity 0:14:31.520 --> 0:14:33.840 did its thing and it pulls out all that stuff 0:14:33.880 --> 0:14:35.960 together and you get a sun, right, So most of 0:14:35.960 --> 0:14:37.560 the stuff went to the Sun, and then you get 0:14:37.640 --> 0:14:40.440 a disc of stuff that's rotating around the Sun. It's 0:14:40.480 --> 0:14:44.120 like rings around the Sun. And then the gravity pulls 0:14:44.160 --> 0:14:46.960 the stuff in that disc together to turning to turn 0:14:47.040 --> 0:14:50.800 that disc into planets, right, And uh so we think 0:14:50.880 --> 0:14:53.480 that the Solar system started about four and a half 0:14:53.560 --> 0:14:57.720 billion years ago, and it took like a few million 0:14:57.920 --> 0:15:01.040 or a hundred million years to pull all that stuff 0:15:01.040 --> 0:15:04.680 and the disk together into sort of protoplanets. Right. So 0:15:04.720 --> 0:15:06.960 you have this sort of loose collection of stuff that 0:15:07.000 --> 0:15:09.760 gravity is pulled together, and then gravity really gets to 0:15:09.800 --> 0:15:13.200 work and it starts squeezing it and it collects all 0:15:13.200 --> 0:15:15.720 this stuff and the planet heats up and sort of 0:15:15.760 --> 0:15:19.080 melts the metal and you get the iron dropping to 0:15:19.120 --> 0:15:22.640 the core and the crust forming, and so you can 0:15:22.680 --> 0:15:26.000 sort of ask, like, what moment do you count the 0:15:26.120 --> 0:15:28.560 earth forming? Is it like when you have the first 0:15:28.560 --> 0:15:32.360 big cluster of rocks or maybe when it got gravitationally 0:15:32.480 --> 0:15:35.280 heated enough to sort of melt the metals and form 0:15:35.360 --> 0:15:38.240 the core um It's not really very clear. Well, I 0:15:38.240 --> 0:15:41.000 always find this really fascinating because we we talked about 0:15:41.000 --> 0:15:43.880 this the other day, that something like the rings around 0:15:43.880 --> 0:15:47.720 Saturn are only temporary, right, Like at some point those 0:15:47.800 --> 0:15:51.760 rings might turn into little blobs. That's right. Gravity is 0:15:52.000 --> 0:15:55.240 very weak but very very patient, and so it just 0:15:55.360 --> 0:15:57.840 keeps working and you give it enough time, it will 0:15:57.880 --> 0:16:01.120 gather things together. And so this stuff that's orbiting Saturn 0:16:01.200 --> 0:16:04.800 eventually grab gravity will pull it together in two moons. 0:16:05.080 --> 0:16:07.920 Even the asteroid belt, is that at some point gonna 0:16:08.040 --> 0:16:11.080 turn into more planets for our Solar system? Yeah, eventually. 0:16:11.080 --> 0:16:13.280 Gravity it means very slow and those things are mostly 0:16:13.280 --> 0:16:16.520 stable orbits, but eventually that stuff will get pulled together. 0:16:16.840 --> 0:16:19.520 I mean also there's disruption. Right if you just left 0:16:19.520 --> 0:16:22.280 the Solar system all by itself, then yes, eventually you'll 0:16:22.320 --> 0:16:25.640 just gather together into a smaller and smaller number of objects. 0:16:25.680 --> 0:16:28.120 But this disruption from stuff that comes outside, you know 0:16:28.160 --> 0:16:31.800 and comets things from the word cloud. Um even even 0:16:31.840 --> 0:16:35.320 things like supernovas from other solar system can disrupt things 0:16:35.400 --> 0:16:39.360 happening in our solar system. Um. So, But yes, eventually 0:16:39.360 --> 0:16:41.800 gravity will pull all this stuff together. It's really incredible 0:16:42.160 --> 0:16:45.160 what over over these time scales, what gravity can do. 0:16:45.200 --> 0:16:46.840 And that's one of my favorite things. It's just started 0:16:46.840 --> 0:16:51.080 realizing that these processes are really slow, so things must 0:16:51.120 --> 0:16:53.960 have been around for a super long time to make 0:16:54.000 --> 0:16:57.400 it happen, right right, Well, I guess I would maybe 0:16:57.480 --> 0:17:00.160 count that the birth of the Earth is when it 0:17:00.240 --> 0:17:02.840 was form, you know, when all those asteroids and rocks 0:17:02.880 --> 0:17:06.560 out there clumped together into a ball about the size 0:17:06.560 --> 0:17:09.159 of the ball that we have now, like, you know, 0:17:09.200 --> 0:17:11.480 when when it kind of snapped into shape. I would 0:17:11.600 --> 0:17:15.080 maybe count that as the age of when the Earth started. Yeah, yeah, 0:17:15.119 --> 0:17:18.680 and that's totally reasonable. That's totally reasonable. Um. I think 0:17:18.760 --> 0:17:22.000 one common definition is that you measured the age of 0:17:22.000 --> 0:17:24.320 the Earth is sort of the age of the oldest 0:17:24.480 --> 0:17:27.359 rock in the Earth. And then you can ask the question, 0:17:27.359 --> 0:17:29.160 what does it mean for a rock to be old. 0:17:29.200 --> 0:17:31.640 Like you know, a rock is just a gravitational pulled 0:17:31.680 --> 0:17:35.239 together clump of dust. But rocks are are formed right 0:17:35.240 --> 0:17:37.959 there through melt and then they're cooled. And so the 0:17:37.960 --> 0:17:40.760 age of a rock is usually like the last time 0:17:40.800 --> 0:17:43.359 it was melted, right, So it's the time since it 0:17:43.400 --> 0:17:45.720 was last melted, and so a lot of time people 0:17:45.840 --> 0:17:48.320 just like the time that it cooled off, the last 0:17:48.320 --> 0:17:51.120 time it really chilled out. And so you can imagine 0:17:51.160 --> 0:17:53.159 like all these rocks came together, as you said, and 0:17:53.200 --> 0:17:56.120 formed the Earth and got squeezed together and probably melted 0:17:56.400 --> 0:17:59.200 and then cooled right, and the crust at least cooled, 0:17:59.520 --> 0:18:01.359 and so you can asked, like maybe that last moment 0:18:01.400 --> 0:18:04.120 the last moment of cooling of the crust. So the 0:18:04.160 --> 0:18:07.040 age of the oldest cooled rock on the Earth could 0:18:07.080 --> 0:18:09.280 be a definition at the age of the Earth, because otherwise, 0:18:09.280 --> 0:18:11.800 how do you know when these rocks came together? Right? 0:18:12.600 --> 0:18:15.720 Otherwise I don't know unless you have, like you know, 0:18:15.920 --> 0:18:18.919 CCTV of the formation of the Solar system. It's pretty 0:18:18.920 --> 0:18:21.560 hard to pin that down. Or you could say, is 0:18:21.560 --> 0:18:23.359 it well, but you just gave me a number you 0:18:23.400 --> 0:18:25.280 said that it was maybe it took around a hundred 0:18:25.320 --> 0:18:29.240 million years to to form that the ball of the Earth. Yeah, 0:18:29.280 --> 0:18:31.600 that's you know, I said, I said between a few 0:18:31.680 --> 0:18:33.920 and a hundred million years, right, So that's a pretty 0:18:33.920 --> 0:18:36.679 big uncertainty. Um, we don't really know how long it 0:18:36.760 --> 0:18:38.840 took and and what moment do you define, like do 0:18:38.840 --> 0:18:41.840 you needed one more rock? Because you know, caustic stuff 0:18:41.960 --> 0:18:45.000 kept getting added to the Earth, and so some people say, well, 0:18:45.080 --> 0:18:46.720 the age of the Earth is sort of just just 0:18:46.880 --> 0:18:49.200 just call it the age of the Solar System because 0:18:49.200 --> 0:18:51.560 that's pretty close to the age of the Earth. Or 0:18:51.680 --> 0:18:54.320 you could say it's the age of the the oldest 0:18:54.440 --> 0:18:56.760 rock on the Earth. So I think both of those 0:18:56.800 --> 0:18:59.199 are sort of acceptable. And anyway, that's really all we 0:18:59.240 --> 0:19:01.800 can probe and end. What we do is we measured 0:19:01.800 --> 0:19:03.919 the age of the oldest rock we can find on 0:19:03.960 --> 0:19:06.199 the Earth, and we say that's pretty close to the 0:19:06.200 --> 0:19:08.480 age of the Earth. So the time that it formed 0:19:08.480 --> 0:19:11.960 into a ball is kind of in between those two numbers, right, Yeah, exactly, 0:19:12.000 --> 0:19:16.640 it's between when the Solar System formed and when the 0:19:16.640 --> 0:19:21.240 ball that is the Earth started getting crusty. Exactly exactly 0:19:21.240 --> 0:19:24.240 when it started getting crusty and grumpy and eating desserted 0:19:24.320 --> 0:19:28.840 parties and going home early like a teenager. The suwhere 0:19:28.880 --> 0:19:32.280 between conception and teenage years that's when you're born. That's 0:19:32.440 --> 0:19:34.080 that's right. And you know, we have the same question 0:19:34.080 --> 0:19:37.720 about people, right, I wonder about that sometimes. You know, Um, 0:19:38.000 --> 0:19:40.720 how do you count somebody's age if there if somebody 0:19:40.800 --> 0:19:44.280 is born premature, they're older. You know, even then somebody 0:19:44.280 --> 0:19:46.359 who was born it was conceived at the same moment 0:19:46.400 --> 0:19:49.360 but then born at full term. So even the age 0:19:49.359 --> 0:19:52.040 of people is sort of hard to define sometimes. All right, well, 0:19:52.080 --> 0:19:55.200 we've determined, we've determined what we mean by the age 0:19:55.240 --> 0:19:57.360 of the Earth, and so now let's get into how 0:19:57.400 --> 0:20:00.119 we know how old the Earth is and what what 0:20:00.160 --> 0:20:15.200 that means. But first let's take a quick break. Okay, 0:20:15.240 --> 0:20:17.720 so we're defining the age of the Earth is how 0:20:17.800 --> 0:20:23.159 old the oldest rock was formed that we know about 0:20:23.480 --> 0:20:26.440 right on Earth. That's right, exactly. Let's say, so when 0:20:26.440 --> 0:20:29.120 the Earth was like a ball of lava, that doesn't count. 0:20:29.280 --> 0:20:33.119 But once it started solidifying, then we're saying that's when 0:20:33.160 --> 0:20:36.760 the Earth was born. Yeah, exactly, because we're imagining that, Yeah, 0:20:36.800 --> 0:20:39.000