1 00:00:01,920 --> 00:00:06,520 Speaker 1: Welcome to brain Stuff production of I Heart Radio. Hey 2 00:00:06,559 --> 00:00:09,360 Speaker 1: brain Stuff, Lauren bog Obam here with a classic episode 3 00:00:09,360 --> 00:00:12,440 Speaker 1: from our previous host, Christian Sagar. In this one, we 4 00:00:12,520 --> 00:00:15,800 Speaker 1: wanted to explore why there have been billions of living 5 00:00:15,840 --> 00:00:18,560 Speaker 1: things on this earth across billions of years that life 6 00:00:18,600 --> 00:00:22,239 Speaker 1: has existed, but only a very few have left direct 7 00:00:22,480 --> 00:00:28,400 Speaker 1: fossil evidence. Hey brain Stuff, it's me Christian Sager. You know, 8 00:00:28,680 --> 00:00:31,400 Speaker 1: when I'm digging a six ft hole in the middle 9 00:00:31,400 --> 00:00:34,080 Speaker 1: of the desert, I start to wonder where are all 10 00:00:34,120 --> 00:00:37,360 Speaker 1: the dead animals? Shouldn't we be waiting knee deep in 11 00:00:37,479 --> 00:00:40,519 Speaker 1: fossils every time we go outside. I know that's morbid, 12 00:00:40,720 --> 00:00:44,080 Speaker 1: but you can probably guess that not every animal that 13 00:00:44,200 --> 00:00:48,560 Speaker 1: dies leaves behind fossil evidence. But why is that? Well, 14 00:00:48,760 --> 00:00:51,840 Speaker 1: just to get our terms straight, a fossil is any 15 00:00:51,920 --> 00:00:55,800 Speaker 1: physical remnant left behind by an organism that died long ago. 16 00:00:56,280 --> 00:00:59,680 Speaker 1: In many cases, fossils might only be things like preserved 17 00:00:59,720 --> 00:01:03,639 Speaker 1: foot prints or nest sites. But today we're looking at 18 00:01:03,680 --> 00:01:07,959 Speaker 1: direct remains of animal bodies, like bones. The likelihood that 19 00:01:08,040 --> 00:01:12,839 Speaker 1: any particular animal body will become fossilized is amazingly small. 20 00:01:12,920 --> 00:01:15,880 Speaker 1: It's actually less than one percent so let's look at 21 00:01:15,920 --> 00:01:20,200 Speaker 1: the stations of the obstacle course to fossilization. First, there's 22 00:01:20,240 --> 00:01:24,000 Speaker 1: body type. Fossilization has a strong preference for animals with 23 00:01:24,200 --> 00:01:28,800 Speaker 1: hard body parts like bones, teeth, and shells. Animals with 24 00:01:28,880 --> 00:01:32,280 Speaker 1: soft bodies like slugs and jellyfish, well, they usually just 25 00:01:32,360 --> 00:01:36,120 Speaker 1: decompose completely and disappear after death, and except in a 26 00:01:36,440 --> 00:01:41,080 Speaker 1: very few rare cases like freezing, dry momification and peat 27 00:01:41,160 --> 00:01:44,839 Speaker 1: bog preservation, the same thing happens to the soft tissues 28 00:01:44,920 --> 00:01:50,040 Speaker 1: on all animal bodies skin, organs, eyeballs, et cetera. They 29 00:01:50,080 --> 00:01:54,360 Speaker 1: all make excellent meals from microorganisms and are thus consigned 30 00:01:54,360 --> 00:01:58,640 Speaker 1: to the ravages of rot. The second main hurdle defossilization 31 00:01:59,080 --> 00:02:02,040 Speaker 1: is exposure. To become a fossil, you need to be 32 00:02:02,160 --> 00:02:05,280 Speaker 1: one of the rare animal bodies that is rapidly buried 33 00:02:05,400 --> 00:02:09,200 Speaker 1: soon after the animal dies. This is most likely to 34 00:02:09,280 --> 00:02:12,080 Speaker 1: happen in or near the site of a moving body 35 00:02:12,120 --> 00:02:15,400 Speaker 1: of water, like a river or a floodplain, where runoff 36 00:02:15,639 --> 00:02:19,560 Speaker 1: floodwaters or regular flow may quickly cover a dead body 37 00:02:19,560 --> 00:02:24,000 Speaker 1: in sediment. It might also happen in arid desert settings, 38 00:02:24,000 --> 00:02:27,640 Speaker 1: where wind can quickly bury animal remains in sand dunes. 39 00:02:28,040 --> 00:02:32,320 Speaker 1: If the remains are not rapidly buried, scavenging animals are 40 00:02:32,360 --> 00:02:36,240 Speaker 1: likely to scatter and then consume them. After all, nature 41 00:02:36,320 --> 00:02:39,000 Speaker 1: hates to pass up a free lunch, and even a 42 00:02:39,040 --> 00:02:43,119 Speaker 1: clean skeleton left out exposed to the elements will eventually 43 00:02:43,160 --> 00:02:48,520 Speaker 1: be erased by the ravages of the weather. That's decalcification, erosion, 44 00:02:48,840 --> 00:02:52,799 Speaker 1: and corrosion. But let's say your bones are lucky enough 45 00:02:52,840 --> 00:02:56,239 Speaker 1: to be rapidly buried somehow. The next big hurdle is 46 00:02:56,280 --> 00:03:00,320 Speaker 1: a sediment itself. A nice dry sand or alkaline mud 47 00:03:00,400 --> 00:03:02,640 Speaker 1: might be a good place to become a fossil, but 48 00:03:02,720 --> 00:03:05,280 Speaker 1: if your bones are buried in soil with a higher 49 00:03:05,320 --> 00:03:09,440 Speaker 1: temperature and higher acidity, your prospects are a lot slimmer. 50 00:03:09,760 --> 00:03:13,080 Speaker 1: Acidic environments, meaning soils with a low pH tend to 51 00:03:13,160 --> 00:03:17,440 Speaker 1: dissolve hydro zappatite, a calcium phosphate mineral that is a 52 00:03:17,560 --> 00:03:21,639 Speaker 1: main structural ingredient in our bones. So many soil types 53 00:03:21,680 --> 00:03:25,880 Speaker 1: on Earth will simply destroy all the bones they swallow. 54 00:03:26,160 --> 00:03:30,160 Speaker 1: But even in friendly sediment, over a long enough period 55 00:03:30,200 --> 00:03:33,720 Speaker 1: of time, bones can break down the organic proteins and 56 00:03:33,800 --> 00:03:38,680 Speaker 1: bones like collagen, eventually decompose and the inorganic molecules, and 57 00:03:38,720 --> 00:03:43,640 Speaker 1: bones can be crushed, dissolved, or otherwise destroyed by physical 58 00:03:43,680 --> 00:03:47,720 Speaker 1: force over the centuries. So if you want your actual 59 00:03:47,840 --> 00:03:50,960 Speaker 1: bone structure to survive, you have to be lucky enough 60 00:03:51,040 --> 00:03:55,840 Speaker 1: to undergo a little transformation. Most really ancient bones we find, 61 00:03:55,880 --> 00:03:59,480 Speaker 1: such as dinosaur bones, aren't the unaltered original bones that 62 00:03:59,560 --> 00:04:02,640 Speaker 1: were bare eed millions of years ago. Instead, they're either 63 00:04:02,880 --> 00:04:09,000 Speaker 1: a minerally modified versions of those bones or be stone photocopies. 64 00:04:09,480 --> 00:04:14,119 Speaker 1: Two processes represent the majority of these cases, perma mineralization 65 00:04:14,280 --> 00:04:19,599 Speaker 1: and replacement. In perma mineralization, mineral rich water seeps into 66 00:04:19,640 --> 00:04:22,159 Speaker 1: the buried bones and fills the pores of the bones 67 00:04:22,360 --> 00:04:26,720 Speaker 1: with its mineral content. These minerals form crystals inside the bones, 68 00:04:26,800 --> 00:04:30,279 Speaker 1: causing them to modify and harden over time. Sometimes this 69 00:04:30,360 --> 00:04:34,920 Speaker 1: process is also called petrification. In replacement, the original bones 70 00:04:34,960 --> 00:04:39,200 Speaker 1: can be completely dissolved but still leave fossil copies as 71 00:04:39,240 --> 00:04:43,640 Speaker 1: the mineral in the groundwater completely replaces the shape of 72 00:04:43,680 --> 00:04:47,800 Speaker 1: the bones over long periods of time. So let's say 73 00:04:47,880 --> 00:04:51,679 Speaker 1: you're the rare dead animal that wins the fossilization lottery, 74 00:04:51,720 --> 00:04:55,120 Speaker 1: and you just happen to pass all these tests. You 75 00:04:55,160 --> 00:04:57,840 Speaker 1: still have to be found. The total surface of the 76 00:04:57,880 --> 00:05:01,599 Speaker 1: Earth is almost two hundred millions square miles, and even 77 00:05:01,839 --> 00:05:04,400 Speaker 1: for a guy like me, there's only so much time 78 00:05:04,440 --> 00:05:11,200 Speaker 1: to dick. Today's episode was written by Joe McCormick and 79 00:05:11,200 --> 00:05:13,520 Speaker 1: produced by Tyler Clang. For more on this and lots 80 00:05:13,520 --> 00:05:15,720 Speaker 1: of other topics, was it how stuff works dot com. 81 00:05:15,760 --> 00:05:18,480 Speaker 1: Brain Stuff is production of iHeart Radio. For more podcasts 82 00:05:18,480 --> 00:05:20,440 Speaker 1: in My heart Radio, visit the i heart Radio app, 83 00:05:20,600 --> 00:05:23,240 Speaker 1: Apple Podcasts, or wherever you listen to your favorite shows.