Hey Brainstuff -- it’s me, Jonathan.
You know, sometimes in a lull between events
at CES I’m digging a six-foot hole in the
middle of the desert outside Las Vegas and
I start to wonder: Where are all the dead
animals?
Shouldn’t we be wading knee-deep in fossils
every time we go outside?
You can probably guess that not every animal
that dies leaves behind fossil evidence.
But why is that?
Just to get our terms straight, a fossil is
any physical remnant left behind by an organism
that died long ago.
In many cases, fossils might only be things
like preserved footprints or nest sites.
But today, we’re looking at direct remains
of animal bodies, like bones.
The likelihood that any particular animal
body will become fossilized is amazingly small,
way less than 1%.
You might as well buy a lottery ticket.
So let’s look at the stations of the obstacle
course to fossilization:
First, there’s body type.
Fossilization has a strong preference for
animals with hard body parts, like bones,
teeth and shells.
Animals with soft bodies, like slugs and jellyfish,
will usually just decompose completely and
disappear after death.
The second main hurdle to fossilization is
exposure.
To become a fossil, you need to be one of
the rare animal bodies that is rapidly buried
soon after the animal dies.
This is most likely to happen in or near the
site of a moving body of water, like a river
or a flood plain, where runoff, floodwaters
or regular flow may quickly cover a dead body
in sediment.
It might also happen in arid desert settings,
where wind can quickly bury animal remains
in sand dunes.
If the remains are not rapidly buried, scavenging
animals are likely to scatter and consume
them -- after all, nature hates to pass up
a free lunch.
We're alike in that way.
And even a clean skeleton left out exposed
to the elements will eventually be erased
by decalcification, erosion and corrosion.
But let’s say your bones are lucky enough
to be rapidly buried somehow.
The next big hurdle is the sediment itself.
A nice dry sand or alkaline mud might be a
good place to become a fossil.
But if your bones are buried in soil with
a higher temperature and higher acidity, your
prospects are a lot slimmer.
Acidic environments (meaning soils with a
low pH) tend to dissolve hydroxyapatite -- a
calcium phosphate mineral that is a main structural
ingredient in our bones.
So, many soil types on Earth will simply destroy
all the bones they swallow.
I'm counting on it.
(I kid, I kid)
But even in friendly sediment, over a long
enough period of time, bones can break down.
The organic proteins in bones, like collagen,
eventually decompose, and the inorganic minerals
in bones can be crushed, dissolved or otherwise
destroyed by physical forces over the centuries.
So if you want your actual bone structure
to survive, you have to be lucky enough to
undergo a little transformation.
Most really ancient bones we find, such as
dinosaur bones, aren’t the unaltered, original
bones that were buried millions of years ago,
but either minerally modified versions of
those bones, or “stone photocopies.”
Two processes represent the majority of these
cases: permineralization, and replacement.
In permineralization, mineral-rich water seeps
into the buried bones and fills the pores
of the bones with its mineral content.
These minerals form crystals inside the bones,
causing them to modify and harden over time.
Sometimes this process is also called “petrification.”
In “replacement,” the original bones can
be completely dissolved, but still leave fossil
copies, as the minerals in the groundwater
completely replace the shape of the bones
over long periods of time.
So let’s say you’re the rare dead animal
that wins the fossilization lottery, and you
just happen to pass ALL these tests?
You still have to be found.
The total surface of the Earth is almost 200
million square miles, and even for a guy like
me, there’s only so much time to dig.
Do you have another question about fossils?
Let us know in the comments, and we might
be able to answer it in a future episode!
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And of course, if you want to learn more about
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