being chipped out of the La Brea Tar Pits.

It's been hiding here in Los Angeles, perfectly preserved,

for anywhere from 25,000 to 45,000 years.

Scientists have spent more than a century

excavating some 4 million specimens from the pits.

But why keep adding to an already huge collection?

Because each new fossil helps fill in the gaps

on a 50,000-year timeline of life in the region,

spanning to the end of the Stone Age.

We went to the La Brea Tar Pits

to see how specimens are discovered, cleaned,

and pieced together to build that record.

The process kicks off with a sticky scavenger hunt.

There are around 130 pits at the tar pits,

which is technically a misnomer.

Laura: We don't technically have tar.

We don't naturally have pits.

What we actually have is asphalt,

which is the crudest form of naturally occurring oil.

Narrator: Some tar pits are still connected

to their oil source, like this one.

So, right now I'm in pit 91, which was the 91st pit.

I know, fancy naming schemes.

Narrator: Others become disconnected

from their oil source and dry out.

Huge, dry chunks of the deposit

are easier to move into separate boxes for excavation.

Right now I'm in box 13, which is 13 of 23,

as you might be able to guess.

This particular box has

easily tens of thousands of fossils in it.

Narrator: The excavation process isn't as simple

as pulling a bone out of some goo.

Laura: So, sometimes I'll find a fossil

and be able to excavate it out in, like, 15 minutes.

And sometimes I'm looking at a fossil for several months,

definitely not dreaming about it teasing me.

Narrator: Take this saber-toothed cat skull,

which has been weeks in the works.

Based on 16 years of experience,

Laura can estimate how many fossils are in a given deposit.

To start her search, Laura first sets up a makeshift grid.

This will help Laura keep track

of where and in what position fossils are found,

since the asphalt is too dense

for traditional radar to provide initial images.

Laura: It's eyeballs and elbow grease.

Narrator: Then she begins the meticulous process

of carving the skull out of the matrix that encases it.

Laura: If I am confident that I'm not going to find fossils,

I'll have things like hammers and chisels

that I'll be able to get in there

and move some of those things away.

Narrator: This is where it gets tricky.

Asphalt actually protects the bones' organic matter.

This also makes them more fragile

than traditional stone fossils.

Around the fossils themselves

we'll start with very small tools,

something like this dental pick,

which, yes, is sourced from local dentists.

Thank you for your donations.

And sometimes I'm using it

the same way that a dentist would, with the tip of it,

and sometimes I'm using it more like a clay-sculpting tool,

kind of pulling sediment away from fossils.

And then sometimes you'll also see me

using a natural-bristle paintbrush.

I don't want to use plastic bristles, because the oil

will actually eventually degrade those bristles,

and they'll kind of melt a little bit,

which isn't good for anybody.

Narrator: Excavators tailor their strategy

to preserve not only the delicate bones,

but also the matrix itself.

It's filled with valuable microfossils.

Laura: So, we're going to pour that chemical solvent

in there.

So, this particular one is a Novec 73DE.

And so that's a chemical degreaser.

Narrator: The solvent dissolves the asphalt

and leaves behind treasures.

Laura: This one is the end of a tibiotarsus, or a drumstick.

This one's bigger than a chicken.

And we also have plant fossils as well.

Narrator: Once the matrix is collected

and surrounding sediment is cleared ...

Laura: So, I should be able to just

kind of gently release the fossil

from this tangle

and send it on to the laboratory.

Narrator: Where preparators will put in even more hours

into this one saber-toothed cat skull.

To make sure our skull is shelf-stable,

preparators start with a more meticulous asphalt removal.

Stephany: I would say that this could probably take me

up to 10 hours in total to complete.

Narrator: Stephany uses more degreaser

and a collection of cotton swabs, foam applicators,

brushes, and picks to surface-clean the skull.

Stephany: When we have areas

where there is jagged bone exposed,

we prefer to use the foam-tip applicators,

because there's no grabbing of fibers

that could damage the fossil

or transfer too much fiber onto the fossil.

It's very much like painting, almost.

Narrator: The asphalt permanently stains the fossil

a deep brown.

Stephany: You will notice that as I work through this,

the tool itself is changing color and becoming darker.

Narrator: Now, her goal isn't to deep clean the specimen;

it's to prevent deterioration over time,

so some debris stays behind.

Stephany: We leave the internal matrix in the skull

because it provides structural support and stability.

Narrator: If a fossil is damaged

or comes out of the pit in pieces, it can be fixed.

Stephany: So, this is a canine from box nine,

and we prepared this bit in September last year

and sent it through to collections.

And then in May this year, we found the tip,

and when we put it in there, it was like a puzzle piece.

So, this is the lower jaw, or dentary,

of a young dire wolf that we have over here.

Narrator: She uses a little adhesive

and sometimes Japanese kozo paper

to secure and stabilize the broken bits.

Stephany: So, kozo paper is a Japanese archival paper.

You'll notice that I tore it,

and we want to have these fibers.

Think of when you walk into a spider web.

It just feels like it's everywhere.

They migrate and then catch onto the specimen

and really anchor well onto it.

Narrator: And the final step is covering the entire specimen

in the same adhesive used for repairs.

This seals and protects the organic material.

If somewhere down the line

a researcher needs to access that material ...

Stephany: Because we use acetone,

it makes the whole process reversible.

Narrator: After preparation ...

Stephany: The specimen then gets its own

individual catalog number

and then forms part of our already amazing collection

that spans over 3½ million specimens.

Emily: We have somewhere in the nature

of at least 2,500 saber-toothed cats.

So, for instance, all of these drawers here

are full of nothing but left upper-arm bones

of saber-toothed cats

from just one of our about 130 deposits.

Narrator: Beyond saber-toothed cats,

the La Brea collection contains

around 4 million specimens from the last 50,000 years.

And the biggest extinction event since the dinosaurs,

the Ice Age extinctions, ramped up 12,000 years ago.

Emily: The majority of large mammals on Earth

disappeared during this time.

It's been really hard to figure out exactly when,

because we just don't have enough fossils.

Narrator: These bountiful tar pits are an exception.

Emily: This is the only place on Earth

where we have a time-transgressive record

over a 40,000-year period of many of these species,

and this allows us to do research

that you can't really do at any other fossil site.

Narrator: Along with the when,

researchers can answer questions

about why species when extinct, too.

Emily: Was it lack of water sources?

Was it an area getting too hot or too cold?

Was it increase in fire?

Was it something to do with

the arrival of humans on the landscape?

Narrator: Some unique specimens can tell us

about an entire species' behavior

almost entirely on their own.

Take this elderly saber-toothed cat with hip dysplasia.

The fact that it exists at all ...

Emily: Is an indication that this species

was probably social,

because individuals with injuries or pathologies like this

probably wouldn't have been able to hunt for themselves

and probably relied on a social group

or a family group to support them.

Narrator: While the lab pieces together specimens,

collections pieces together data.

Emily: Understanding what sort of processes

might have been happening

during the last major extinction event

could be really important for helping us to weather

some of these unprecedented-in-human-history impacts

that we're experiencing.

And there is basically no more important question

to be asking today.

Narrator: Knowing how creatures

lived amidst climate change in the past

might help humans learn to navigate

extreme conditions in the future,

like wildfires or droughts.

In this case, the more we have, the more we know.

And there are no plans to stop digging anytime soon.