Speaker 1: Welcome to brain Stuff production of I Heart Radio. Hey
Speaker 1: brain Stuff, Lauren bog Obam here with a classic episode
Speaker 1: from our previous host, Christian Sagar. In this one, we
Speaker 1: wanted to explore why there have been billions of living
Speaker 1: things on this earth across billions of years that life
Speaker 1: has existed, but only a very few have left direct
Speaker 1: fossil evidence. Hey brain Stuff, it's me Christian Sager. You know,
Speaker 1: when I'm digging a six ft hole in the middle
Speaker 1: of the desert, I start to wonder where are all
Speaker 1: the dead animals? Shouldn't we be waiting knee deep in
Speaker 1: fossils every time we go outside. I know that's morbid,
Speaker 1: but you can probably guess that not every animal that
Speaker 1: dies leaves behind fossil evidence. But why is that? Well,
Speaker 1: just to get our terms straight, a fossil is any
Speaker 1: physical remnant left behind by an organism that died long ago.
Speaker 1: In many cases, fossils might only be things like preserved
Speaker 1: foot prints or nest sites. But today we're looking at
Speaker 1: direct remains of animal bodies, like bones. The likelihood that
Speaker 1: any particular animal body will become fossilized is amazingly small.
Speaker 1: It's actually less than one percent so let's look at
Speaker 1: the stations of the obstacle course to fossilization. First, there's
Speaker 1: body type. Fossilization has a strong preference for animals with
Speaker 1: hard body parts like bones, teeth, and shells. Animals with
Speaker 1: soft bodies like slugs and jellyfish, well, they usually just
Speaker 1: decompose completely and disappear after death, and except in a
Speaker 1: very few rare cases like freezing, dry momification and peat
Speaker 1: bog preservation, the same thing happens to the soft tissues
Speaker 1: on all animal bodies skin, organs, eyeballs, et cetera. They
Speaker 1: all make excellent meals from microorganisms and are thus consigned
Speaker 1: to the ravages of rot. The second main hurdle defossilization
Speaker 1: is exposure. To become a fossil, you need to be
Speaker 1: one of the rare animal bodies that is rapidly buried
Speaker 1: soon after the animal dies. This is most likely to
Speaker 1: happen in or near the site of a moving body
Speaker 1: of water, like a river or a floodplain, where runoff
Speaker 1: floodwaters or regular flow may quickly cover a dead body
Speaker 1: in sediment. It might also happen in arid desert settings,
Speaker 1: where wind can quickly bury animal remains in sand dunes.
Speaker 1: If the remains are not rapidly buried, scavenging animals are
Speaker 1: likely to scatter and then consume them. After all, nature
Speaker 1: hates to pass up a free lunch, and even a
Speaker 1: clean skeleton left out exposed to the elements will eventually
Speaker 1: be erased by the ravages of the weather. That's decalcification, erosion,
Speaker 1: and corrosion. But let's say your bones are lucky enough
Speaker 1: to be rapidly buried somehow. The next big hurdle is
Speaker 1: a sediment itself. A nice dry sand or alkaline mud
Speaker 1: might be a good place to become a fossil, but
Speaker 1: if your bones are buried in soil with a higher
Speaker 1: temperature and higher acidity, your prospects are a lot slimmer.
Speaker 1: Acidic environments, meaning soils with a low pH tend to
Speaker 1: dissolve hydro zappatite, a calcium phosphate mineral that is a
Speaker 1: main structural ingredient in our bones. So many soil types
Speaker 1: on Earth will simply destroy all the bones they swallow.
Speaker 1: But even in friendly sediment, over a long enough period
Speaker 1: of time, bones can break down the organic proteins and
Speaker 1: bones like collagen, eventually decompose and the inorganic molecules, and
Speaker 1: bones can be crushed, dissolved, or otherwise destroyed by physical
Speaker 1: force over the centuries. So if you want your actual
Speaker 1: bone structure to survive, you have to be lucky enough
Speaker 1: to undergo a little transformation. Most really ancient bones we find,
Speaker 1: such as dinosaur bones, aren't the unaltered original bones that
Speaker 1: were bare eed millions of years ago. Instead, they're either
Speaker 1: a minerally modified versions of those bones or be stone photocopies.
Speaker 1: Two processes represent the majority of these cases, perma mineralization
Speaker 1: and replacement. In perma mineralization, mineral rich water seeps into
Speaker 1: the buried bones and fills the pores of the bones
Speaker 1: with its mineral content. These minerals form crystals inside the bones,
Speaker 1: causing them to modify and harden over time. Sometimes this
Speaker 1: process is also called petrification. In replacement, the original bones
Speaker 1: can be completely dissolved but still leave fossil copies as
Speaker 1: the mineral in the groundwater completely replaces the shape of
Speaker 1: the bones over long periods of time. So let's say
Speaker 1: you're the rare dead animal that wins the fossilization lottery,
Speaker 1: and you just happen to pass all these tests. You
Speaker 1: still have to be found. The total surface of the
Speaker 1: Earth is almost two hundred millions square miles, and even
Speaker 1: for a guy like me, there's only so much time
Speaker 1: to dick. Today's episode was written by Joe McCormick and
Speaker 1: produced by Tyler Clang. For more on this and lots
Speaker 1: of other topics, was it how stuff works dot com.
Speaker 1: Brain Stuff is production of iHeart Radio. For more podcasts
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