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Time English (United States) Language 2 Action
00:00
Get ready, because you’re about to look a dinosaur in the face.
00:03
This is a nodosaur.
00:05
In its belly, you can still see specks of its last meal.
00:08
Fern salad.
00:09
From the traces of melanin in its bumpy skin,
00:11
we can wager that it was reddish-brown with a light underbelly.
00:14
And those toe beans still look squishable— even though they’ve turned to stone.
00:18
Don’t you just wanna squeeze ‘em?
00:19
Turns out, the worst day of this nodosaur’s life was a very lucky day for making a fossil.
00:24
Hi, I’m Sage and this is Crash Course Geology.
00:27
[THEME MUSIC]
00:31
This is poop.
00:32
And it’s a fossil.
00:33
This is a bug bedazzled in fool’s gold.
00:35
And it’s a fossil.
00:36
This baby cave lion unearthed from permafrost?
00:39
This worm sperm?
00:40
This ant with a parasitic mushroom growing out of its butt?
00:43
All fossils.
00:44
Fossils are preserved remains or traces of organisms that are at least 10,000 years old.
00:50
But they aren’t just shells and bones, ammonite necklaces and t-rex thighs.
00:54
Fossils can also preserve skin, feathers, or flowers.
00:58
They can freeze footprints, tunnels, and nests in time.
01:02
Even whole baby mammoths!
01:03
Fossils are the closest we’ll ever get to long-gone organisms.
01:07
And often, they’re a snapshot of their last, worst days.
01:12
But even though everyone dies, very few fossilize.
01:16
Actually becoming a fossil is like winning the geological jackpot.
01:20
You see, fossils require very specific conditions to exist at all.
01:24
Most fossils form when living things are quickly trapped and buried in sediment,
01:28
like mud, sand, or ash.
01:30
That’s what happened to our nodosaur friend.
01:32
I mean, I consider it a personal friend.
01:34
About 110 million years ago, the nodosaur died… somehow.
01:39
Its body floated down a river, then into the sea, as it… bloated with gas.
01:44
Eventually, the body burst and sank belly-up to the seafloor,
01:49
where mud swirled around and buried it.
01:51
After that initial burial, there are a few different
01:53
ways fossils can form.
01:55
The first path is permineralization.
01:57
That’s when minerals from the water in the ground leech into the pores of buried wood,
02:01
bone, shells, or soft tissue, replace them, and leave behind a heavier, denser 3-D mold.
02:06
As sediment kept layering over our nodosaur,
02:09
minerals infused and replaced much of its armored skin, bones, and squishy bits,
02:13
which eventually hardened into stone. Now that’s what I call rock-hard abs.
02:17
Often, as minerals replace the original tissue, they change color.
02:20
And on rare occasions, they can actually opalize and get all glossy.
02:24
Ooooh, shiny.
02:25
Even so, it can be hard to tell permineralized fossils from regular rocks.
02:29
So allow me, your Internet science talk-talk clown,
02:32
to let you in on a professional secret that real paleontologists use in the field:
02:36
you lick ‘em.
02:37
No, really.
02:38
Bone is more porous than rock.
02:39
So, if it sticks to your tongue, it’s probably fossilized bone.
02:42
Dwayne, may I?
02:46
Actually, you know what?
02:47
I like our relationship as it is.
02:50
By the way, if you think minerals are as neat as I do,
02:52
you’re gonna want to check out the SciShow Rocks Box.
02:54
They send cool rocks right to your home!
02:56
Check out the link below to learn more.
02:58
Okay, so replacement by minerals— that’s the first path to fossil-hood.
03:02
Another possible path is the ol’ C and C:
03:04
compression and carbonization,
03:06
which usually happens to lightweights like leaves, fish, and insects.
03:09
First, layers of sediment bury an organism until it’s flatter than the acting in a B-movie.
03:14
That’s the compression part.
03:15
Then, as the organic bits decompose, carbonization begins,
03:19
sparking chemical reactions that transform its remains into a filmy carbon silhouette.
03:23
Rest in peace.
03:24
But not all burial by sediment involves preservation of body parts.
03:28
Trace fossils preserve impressions of organisms’ behaviors from long ago,
03:32
like walking, wiggling, or burrowing.
03:35
And they’re no less amazing than preserved skin and bones.
03:38
Like, 11,500 years ago in what’s now New Mexico,
03:42
fossils formed from the footprints of little kids
03:44
who stopped to play in the fresh tracks of a giant ground sloth.
03:48
And honestly?
03:49
Every time I think about this I feel like crying.
03:51
I love us.
03:52
We are very cute animals.
03:53
And some of the rarest, wildest,
03:55
most jaw-dropping fossils don’t involve getting buried under sediment at all.
04:00
In fact, there’s quite a few methods to choose from. Let’s hear a word from our sponsor…
04:04
Are you dead? Or about to be?
04:07
We here at the Preservation Station
04:09
offer bespoke fossilization services for the discerning organism.
04:15
Whether it’s an amber tomb, or a desert cave, or a 10,000-year deep-freeze,
04:21
we’ll match you with a special environment that will preserve all, or most, of your body,
04:27
so you can look almost as good as the day you died.
04:32
When it works, it really works.
04:35
When it doesn’t?
04:36
Eh. You’re already dead.
04:39
So don’t delay, slow the decomposition of your body today.
04:46
Sign me up!
04:46
Sometimes, in really specific cases, fossils preserve whole bodies, skin and all.
04:50
Like when resin oozes off a tree and seals up a little bug before it can crawl away—
04:54
hardening into tiny, transparent geologic coffins we call amber.
04:58
Or when a creature dies in a desert cave and dries out, becoming a mummy.
05:02
Some exceptional fossils have formed from organisms that landed in tar pits or bogs,
05:07
while others have been found frozen in ice.
05:09
That slows down decomposition by a lot—
05:12
keeping skin, hair, and even whiskers intact against all odds.
05:15
And I do mean all odds.
05:17
In the scheme of everything that’s lived and died on our planet, fossilization is very rare.
05:23
Usually, organisms rest in pieces, which get broken down and recycled—
05:27
either by other organisms or geological processes.
05:30
But two main factors increase the odds of winning the fossilization lottery.
05:34
Number one: rapid burial by sediment soon after death.
05:37
That makes it more likely the remains will settle in place, undisturbed.
05:41
And number two: burial of a tough body part.
05:44
Hard bits like shells, bones, and teeth have better odds of fossilizing than soft tissue,
05:49
which decomposes very easily.
05:51
But it’s not just extraordinary to become a fossil.
05:54
It’s extraordinary for a fossil to stick around long enough for us to find it.
05:58
Erosion and weathering are constantly wiping the geologic record clean
06:02
like a big Etch A Sketch.
06:03
Because Earth’s surface is constantly changing, the fossil record will always be incomplete.
06:09
So the nodosaur fossil really beat the odds.