Get ready, because you’re about to look a dinosaur in the face.

This is a nodosaur. In its belly, you can still see specks of its last meal.

Fern salad. From the traces of melanin in its bumpy skin, we can wager that it was reddish-brown with a light underbelly. And those toe beans still look squishable— even though they’ve turned to stone.

Don’t you just wanna squeeze ‘em? Turns out, the worst day of this nodosaur’s life was a very lucky day for making a fossil. Hi, I’m Sage and this is Crash Course Geology. [THEME MUSIC] This is poop.

And it’s a fossil. This is a bug bedazzled in fool’s gold. And it’s a fossil.

This baby cave lion unearthed from permafrost? This worm sperm? This ant with a parasitic mushroom growing out of its butt?

All fossils. Fossils are preserved remains or traces of organisms that are at least 10,000 years old. But they aren’t just shells and bones, ammonite necklaces and t-rex thighs.

Fossils can also preserve skin, feathers, or flowers. They can freeze footprints, tunnels, and nests in time. Even whole baby mammoths!

Fossils are the closest we’ll ever get to long-gone organisms. And often, they’re a snapshot of their last, worst days. But even though everyone dies, very few fossilize.

Actually becoming a fossil is like winning the geological jackpot. You see, fossils require very specific conditions to exist at all. Most fossils form when living things are quickly trapped and buried in sediment, like mud, sand, or ash.

That’s what happened to our nodosaur friend. I mean, I consider it a personal friend. About 110 million years ago, the nodosaur died… somehow.

Its body floated down a river, then into the sea, as it… bloated with gas. Eventually, the body burst and sank belly-up to the seafloor, where mud swirled around and buried it. After that initial burial,  there are a few different  ways fossils can form.

The first path is permineralization. That’s when minerals from the water in the ground leech into the pores of buried wood, bone, shells, or soft tissue, replace them, and leave behind a heavier, denser 3-D mold. As sediment kept layering over our nodosaur, minerals infused and replaced much of its armored skin, bones, and squishy bits, which eventually hardened into stone.

Now that’s what I call rock-hard abs. Often, as minerals replace the original tissue, they change color. And on rare occasions, they can actually opalize and get all glossy.

Ooooh, shiny. Even so, it can be hard to tell permineralized fossils from regular rocks. So allow me, your Internet science talk-talk clown, to let you in on a professional secret that real paleontologists use in the field: you lick ‘em.

No, really. Bone is more porous than rock. So, if it sticks to your tongue, it’s probably fossilized bone.

Dwayne, may I? Actually, you know what? I like our relationship as it is.

By the way, if you think  minerals are as neat as I do, you’re gonna want to check out the SciShow Rocks Box. They send cool rocks right to your home! Check out the link below to learn more.

Okay, so replacement by minerals— that’s the first path to fossil-hood. Another possible path is the ol’ C and

C: compression and carbonization, which usually happens to lightweights like leaves, fish, and insects. First, layers of sediment bury an organism until it’s flatter than the acting in a B-movie. That’s the compression part. Then, as the organic bits decompose, carbonization begins, sparking chemical reactions that transform its remains into a filmy carbon silhouette.

Rest in peace. But not all burial by sediment involves preservation of body parts. Trace fossils preserve impressions of organisms’ behaviors from long ago, like walking, wiggling, or burrowing.

And they’re no less amazing than preserved skin and bones. Like, 11,500 years ago in what’s now New Mexico, fossils formed from the footprints of little kids who stopped to play in the fresh tracks of a giant ground sloth. And honestly?

Every time I think about this I feel like crying. I love us. We are very cute animals.

And some of the rarest, wildest, most jaw-dropping fossils don’t involve getting buried under sediment at all. In fact, there’s quite a few methods to choose from. Let’s hear a word from our sponsor… Are you dead?

Or about to be? We here at the Preservation Station offer bespoke fossilization services for the discerning organism. Whether it’s an amber tomb, or a desert cave, or a 10,000-year deep-freeze, we’ll match you with a special environment that will preserve all, or most, of your body, so you can look almost as good as the day you died.

When it works, it really works. When it doesn’t? Eh.

You’re already dead. So don’t delay, slow the decomposition of your body today. Sign me up!

Sometimes, in really specific cases, fossils preserve whole bodies, skin and all. Like when resin oozes off a tree and seals up a little bug before it can crawl away— hardening into tiny, transparent geologic coffins we call amber. Or when a creature dies in a desert cave and dries out, becoming a mummy.

Some exceptional fossils have formed from organisms that landed in tar pits or bogs, while others have been found frozen in ice. That slows down decomposition by a lot— keeping skin, hair, and even whiskers intact against all odds. And I do mean all odds.

In the scheme of everything that’s lived and died on our planet, fossilization is very rare. Usually, organisms rest in pieces, which get broken down and recycled— either by other organisms or geological processes. But two main factors increase the odds of winning the fossilization lottery.

Number one: rapid burial by sediment soon after death. That makes it more likely the remains will settle in place, undisturbed. And number two: burial of a tough body part.

Hard bits like shells, bones, and teeth have better odds of fossilizing than soft tissue, which decomposes very easily. But it’s not just extraordinary to become a fossil. It’s extraordinary for a fossil to stick around long enough for us to find it.

Erosion and weathering are constantly wiping the geologic record clean like a big Etch A Sketch. Because Earth’s surface is constantly changing, the fossil record will always be incomplete. So the nodosaur fossil really beat the odds.

First, it became a fossil. Then, it lay undisturbed for millions of years, 250 feet below the surface. And then, it was discovered by chance in 2011, when some oil-sands miners in Alberta, Canada, drilled into it by accident.

As one of them put it, they were “like kids on Christmas morning.” I would be, too, if I got to help dig up a dinosaur. Lucky ducks. When we are lucky enough to find fossils, we can learn a lot about how our planet— and the life it supports— have changed over time.

Let’s check out one of my geology rock stars… Roughly 400 million years ago, a fishy critter managed to leave the sea and walk on land. If it hadn’t, you and I wouldn’t be here right now. But which came first?

Living on land, or evolving legs? Paleontologist Jennifer Clack spent a lot of time thinking about that mystery— when she wasn’t busy riding her motorcycle. By the 1980s, scientists understood how today’s back-boned land animals— including humans— came to be.

They evolved from the first tetrapods, or creatures with four legs, which themselves evolved from the first back-boned creatures that arose in ancient seas. But nobody understood exactly how the transition from living in water to walking on land had happened. So in 1987, Clack headed to Greenland with some colleagues and returned with a trove  of early tetrapod fossils, including a big-mouthed beast she named Boris.

It took years for Clack to extract Boris from the chunk of rock he was fossilized in. But what she discovered was incredible. At the back of Boris’s skull, rod-like structures suggested the creature had  arteries for breathing  through both gills and lungs.

Boris also had legs with feet shaped like paddles. They were too small to fully support the animal’s weight for walking, but they definitely were not fins! As Clack herself put it: Boris was basically “a fish with fingers.” With this fossil, Clack solved the mystery of how our fishy ancestors transitioned from the ocean to the shore.

The legs and lungs came first. Then came life on land. Fossils like Boris and the nodosaur are as close as we can get to witnessing the dramas of the living things that came before us.

Sometimes, really exceptional troves of fossils turn up, like Earth’s storage units. Except they hold way cooler stuff than a couch that doesn’t fit in your apartment. Literally.

They’re called Lagerstätte, which comes from the German words for “storage” and “place.” Lagerstätten can be full of lots of fossils, or a few really well-preserved fossils, or both. Like, in the Canadian Rocky Mountains, the Burgess Shale rock formation teems with fossils from more than half a billion years ago, during the Cambrian period. Some of those early critters are the relatives of today’s animals, including us.

Hi, great-great-great-great-grandpa! And others, like Hallucigenia, are so weird it took scientists over three decades just to figure out where the head was. I think I’m supposed to pet… that end?

Other fossils in the Burgess Shale are evolutionary dead-ends— lifeforms that died out en masse, near the end of the Cambrian. We’re not exactly sure why. But understanding which life survived and evolved in the aftermath of past mass extinctions can help us understand the repercussions of ecological change today.

Pour one out for the trilobites, y’all. Fossils also tell us the story of Earth itself,  and how our life-sustaining  mutha has changed over time. Like, we know that the rocks in today’s mountain ranges formed from ancient seafloors that were forced upwards, thanks to sea creature fossils found on mountaintops.

And fern and reptile fossils found on opposite sides of the world helped us figure out that continents move. Fossils are like Polaroid pictures of a dead thing’s last day on Earth. And they’re also clues to how life has changed and adapted over time, in a big, wild story that includes us— and is still unfolding today.

They invite us to imagine a time and place beyond the little slice we get to live and breathe in. So let’s hear it for the few, the elite, the fossilized. Shout-out to the ant with a mushroom in its butt.

Next time, grab your parka; we’re talking about glaciers. I’ll see you then. Thanks for watching this episode of Crash Course Geology which was filmed at our studio in Indianapolis, Indiana, and was made with the help of all these awesome people.

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