- [Narrator] Like buried treasure,

they lie hidden from sight.

Echoes of an ancient past, they whisper secrets

and tell tales once lost to time.

Fossils are remnants or impressions of ancient organisms

that are naturally preserved in stone.

While there are hundreds of fossil types,

they are often grouped into two major categories,

body fossils, which are the preserved remains

of plants and animals, and trace fossils,

which are records of an animal's behavior,

such as footprints.

Together, they form the fossil record,

a primary account that tells the story

of life on Earth through stone.

Fossilization or the process of preserving

organisms in stone, can occur in countless ways.

These methods are largely grouped

depending on whether the organisms

are altered during the fossilization process.

Fossilization that does not alter a specimen

can help to preserve its original form and texture.

Among many methods, this group includes organisms

that have been frozen,

preserved in tar pits, and mummified.

One special case involves trapping organisms,

oftentimes insects, in amber.

This process begins when an organism is covered

in tree sap.

The sap or resin forms a protective seal

around the entrapped organism.

Over time, the soft resin hardens

and turns into amber

with the organism suspended within.

This process creates a biologically inert tomb

for the organism, allowing its soft tissues

to be remarkably preserved.

Other fossilization methods change the specimen

as it is being preserved.

For instance, carbonization transforms soft tissues

into thin black films of carbon.

In fact, countless layers of carbonized plant material

create a well known fossil fuel, coal.

But one of the most common types of fossilization

that changes a specimen is called permineralization.

Permineralization begins when minerals from water

or the ground enter the pores of dead plant

or animal material.

Over time, the minerals attach themselves,

clinging onto cellular walls

and building a crystalline network in the empty cavities.

This mineralization hardens the bone

and turns it into stone,

thereby preserving its original structure in fossil form.

When conditions are right,

fossilization can preserve crucial information

about an organism.

Permineralized wood often contains enough information

to identify its tree genus

and sometimes its species.

Insects encased in amber have been so well preserved

that their genetic material was extracted

and partially sequenced.

And footprints left behind by ancient hominids

help paint a picture of what life was like

for early human ancestors millions of years ago.

With every fossil uncovered,

the planet's ancient past becomes clearer,

helping shape our understanding of our world today.

(gentle music)