Sounds impossible, doesn't it?

It's not.

And the answer relies on a formula that all paleontologists use.

And I'm going to tell you the secret.

First, find rocks of the right age.

Second, those rocks must be sedimentary rocks.

And third, layers of those rocks must be naturally exposed.

That's it.

Find those three things and get yourself on the ground,

chances are good that you will find fossils.

Now let me break down this formula.

Organisms exist only during certain geological intervals.

So you have to find rocks of the right age,

depending on what your interests are.

If you want to find trilobites,

you have to find the really, really old rocks of the Paleozoic --

rocks between a half a billion and a quarter-billion years old.

Now, if you want to find dinosaurs,

don't look in the Paleozoic, you won't find them.

They hadn't evolved yet.

You have to find the younger rocks of the Mesozoic,

and in the case of dinosaurs,

between 235 and 66 million years ago.

Now, it's fairly easy to find rocks of the right age at this point,

because the Earth is, to a coarse degree,

geologically mapped.

This is hard-won information.

The annals of Earth history are written in rocks,

one chapter upon the next,

such that the oldest pages are on bottom

and the youngest on top.

Now, were it quite that easy, geologists would rejoice.

It's not.

The library of Earth is an old one.

It has no librarian to impose order.

Operating over vast swaths of time,

myriad geological processes offer every possible insult

to the rocks of ages.

Most pages are destroyed soon after being written.

Some pages are overwritten,

creating difficult-to-decipher palimpsests of long-gone landscapes.

Pages that do find sanctuary under the advancing sands of time

are never truly safe.

Unlike the Moon -- our dead, rocky companion --

the Earth is alive, pulsing with creative and destructive forces

that power its geological metabolism.

Lunar rocks brought back by the Apollo astronauts

all date back to about the age of the Solar System.

Moon rocks are forever.

Earth rocks, on the other hand, face the perils of a living lithosphere.

All will suffer ruination,

through some combination of mutilation, compression,

folding, tearing, scorching and baking.

Thus, the volumes of Earth history are incomplete and disheveled.

The library is vast and magnificent --

but decrepit.

And it was this tattered complexity in the rock record

that obscured its meaning until relatively recently.

Nature provided no card catalog for geologists --

this would have to be invented.

Five thousand years after the Sumerians learned to record their thoughts

on clay tablets,

the Earth's volumes remained inscrutable to humans.

We were geologically illiterate,

unaware of the antiquity of our own planet

and ignorant of our connection

to deep time.

It wasn't until the turn of the 19th century

that our blinders were removed,

first, with the publication of James Hutton's "Theory of the Earth,"

in which he told us that the Earth reveals no vestige of a beginning

and no prospect of an end;

and then, with the printing of William Smith's map of Britain,

the first country-scale geological map,

giving us for the first time

predictive insight into where certain types of rocks might occur.

After that, you could say things like,

"If we go over there, we should be in the Jurassic,"

or, "If we go up over that hill, we should find the Cretaceous."

So now, if you want to find trilobites,

get yourself a good geological map

and go to the rocks of the Paleozoic.

If you want to find dinosaurs like I do,

find the rocks of Mesozoic and go there.

Now of course, you can only make a fossil in a sedimentary rock,

a rock made by sand and mud.

You can't have a fossil

in an igneous rock formed by magma, like a granite,

or in a metamorphic rock that's been heated and squeezed.

And you have to get yourself in a desert.

It's not that dinosaurs particularly lived in deserts;

they lived on every land mass

and in every imaginable environment.

It's that you need to go to a place that's a desert today,

a place that doesn't have too many plants covering up the rocks,

and a place where erosion is always exposing new bones at the surface.

So find those three things:

rocks of the right age,

that are sedimentary rocks, in a desert,

and get yourself on the ground,

and you literally walk

until you see a bone sticking out of the rock.

Here's a picture that I took in Southern Patagonia.

Every pebble that you see on the ground there

is a piece of dinosaur bone.

So when you're in that right situation,

it's not a question of whether you'll find fossils or not;

you're going to find fossils.

The question is: Will you find something that is scientifically significant?

And to help with that, I'm going to add a fourth part to our formula,

which is this:

get as far away from other paleontologists as possible.

(Laughter)

It's not that I don't like other paleontologists.

When you go to a place that's relatively unexplored,

you have a much better chance of not only finding fossils

but of finding something that's new to science.

So that's my formula for finding dinosaurs,

and I've applied it all around the world.

In the austral summer of 2004,

I went to the bottom of South America,

to the bottom of Patagonia, Argentina,

to prospect for dinosaurs:

a place that had terrestrial sedimentary rocks of the right age,

in a desert,

a place that had been barely visited by paleontologists.

And we found this.

This is a femur, a thigh bone,

of a giant, plant-eating dinosaur.

That bone is 2.2 meters across.

That's over seven feet long.

Now, unfortunately, that bone was isolated.

We dug and dug and dug, and there wasn't another bone around.

But it made us hungry to go back the next year for more.

And on the first day of that next field season,

I found this: another two-meter femur,

only this time not isolated,

this time associated with 145 other bones

of a giant plant eater.

And after three more hard, really brutal field seasons,

the quarry came to look like this.

And there you see the tail of that great beast wrapping around me.

The giant that lay in this grave, the new species of dinosaur,

we would eventually call "Dreadnoughtus schrani."

Dreadnoughtus was 85 feet from snout to tail.

It stood two-and-a-half stories at the shoulder,

and all fleshed out in life, it weighed 65 tons.

People ask me sometimes, "Was Dreadnoughtus bigger than a T. rex?"

That's the mass of eight or nine T. rex.

Now, one of the really cool things about being a paleontologist

is when you find a new species, you get to name it.

And I've always thought it a shame that these giant, plant-eating dinosaurs

are too often portrayed as passive, lumbering platters of meat

on the landscape.

(Laughter)

They're not.

Big herbivores can be surly, and they can be territorial --

you do not want to mess with a hippo or a rhino or a water buffalo.

The bison in Yellowstone injure far more people than do the grizzly bears.

So can you imagine a big bull, 65-ton Dreadnoughtus

in the breeding season,

defending a territory?

That animal would have been incredibly dangerous,

a menace to all around, and itself would have had nothing to fear.

And thus the name, "Dreadnoughtus,"

or, "fears nothing."

Now, to grow so large,

an animal like Dreadnoughtus would've had to have been

a model of efficiency.

That long neck and long tail help it radiate heat into the environment,

passively controlling its temperature.

And that long neck also serves as a super-efficient feeding mechanism.

Dreadnoughtus could stand in one place and with that neck

clear out a huge envelope of vegetation,

taking in tens of thousands of calories while expending very few.

And these animals evolved a bulldog-like wide-gait stance,

giving them immense stability,

because when you're 65 tons, when you're literally as big as a house,

the penalty for falling over

is death.

Yeah, these animals are big and tough,

but they won't take a blow like that.

Dreadnoughtus falls over, ribs break and pierce lungs.

Organs burst.

If you're a big 65-ton Dreadnoughtus,

you don't get to fall down in life -- even once.

Now, after this particular Dreadnoughtus carcass was buried

and de-fleshed by a multitude of bacteria, worms and insects,

its bones underwent a brief metamorphosis,

exchanging molecules with the groundwater

and becoming more and more like the entombing rock.

As layer upon layer of sediment accumulated,

pressure from all sides weighed in like a stony glove

whose firm and enduring grip held each bone in a stabilizing embrace.

And then came the long ...

nothing.

Epoch after epoch of sameness,

nonevents without number.

All the while, the skeleton lay everlasting and unchanging

in perfect equilibrium

within its rocky grave.

Meanwhile, Earth history unfolded above.

The dinosaurs would reign for another 12 million years

before their hegemony was snuffed out in a fiery apocalypse.

The continents drifted. The mammals rose.

The Ice Age came.

And then, in East Africa,

an unpromising species of ape evolved the odd trick of sentient thought.

These brainy primates were not particularly fast or strong.

But they excelled at covering ground,

and in a remarkable diaspora

surpassing even the dinosaurs' record of territorial conquest,

they dispersed across the planet,

ravishing every ecosystem they encountered,

along the way, inventing culture and metalworking and painting

and dance and music

and science

and rocket ships that would eventually take 12 particularly excellent apes

to the surface of the Moon.

With seven billion peripatetic Homo sapiens on the planet,

it was perhaps inevitable

that one of them would eventually trod on the grave of the magnificent titan

buried beneath the badlands of Southern Patagonia.

I was that ape.

And standing there, alone in the desert,

it was not lost on me

that the chance of any one individual entering the fossil record

is vanishingly small.

But the Earth is very, very old.

And over vast tracts of time, the improbable becomes the probable.

That's the magic of the geological record.

Thus, multitudinous creatures living and dying on an old planet

leave behind immense numbers of fossils,

each one a small miracle,

but collectively, inevitable.

Sixty-six million years ago, an asteroid hits the Earth

and wipes out the dinosaurs.

This easily might not have been.

But we only get one history, and it's the one that we have.

But this particular reality was not inevitable.

The tiniest perturbation of that asteroid far from Earth

would have caused it to miss our planet by a wide margin.

The pivotal, calamitous day during which the dinosaurs were wiped out,

setting the stage for the modern world as we know it

didn't have to be.