Fossils

HOW IS A FOSSIL FORMED?

1. SedimentAn animal is buried by

sediment, such as

volcanic ash or silt,

shortly after it dies. Its

bones are protected

from rotting by the

layer of sediment.

4. ErosionErosion from rain,

rivers, and wind wears

away the remaining

rock layers. Eventually,

erosion or people

digging for fossils will

expose the preserved

remains.

2. LayersMore sediment layers

accumulate above the

animal’s remains, and

minerals, such as silica

(a compound of silicon

and oxygen), slowly

replace the calcium

phosphate in

the bones.

3. MovementMovement of tectonic

plates, or giant rock

slabs that make up

Earth’s surface, lifts

up the sediments and

pushes the fossil

closer to the surface.

Formation of Fossils

5 types of Fossils

• Petrified

• Mold and Cast

• Carbon film

• Trace

• Preserved remains

Petrified

• Water fills spaces in bones with minerals

Cast and Mold

• An imprint is left in the rock, and then filled in with minerals

MOLDS AND CASTS• A mold forms when hard parts of an

organism are buried in sediment,

such as sand, silt, or clay.

• The hard parts completely dissolve

over time, leaving behind a hollow

impression with the organism’s

shape.

MOLD FOSSILThis mold, or imprint, is of

an extinct mollusk called

an ammonite.

• A cast forms from a mold.

• Water with dissolved minerals and

sediment fills the mold’s empty

spaces.

• Minerals and sediment that are left

in the mold make a cast.

CAST FOSSILThis ammonite cast was

discovered in the United

Kingdom.

Carbon Film

• Only the carbon is left from the organism

Trace

• Evidence left by the animal

Preserved remains

• Organism remains close to what it was in life (Usually preserved in amber, ice, etc.)

How do we know how old fossils are?

• Relative dating – Use rock layers to determine which are older and younger

• Absolute dating – Find the actual age of the fossil. One way we do this is carbon dating. All organisms have some radioactive carbon in them and after they die this starts to decay. We can determine how much is left and this tells us the approximate age.

Geologic Time

How fossils give us clues about

Earth’s history• Fossils are a part of that existing ecology that are also

left behind. It can tell us much about its environmental settings.– Includes plant material, animal remains, rocks and minerals.

Fossils are used for examining

Earths History.• The fossil record provides

evidence about the history of life and past environments on Earth.

• The fossil records also show how different groups of organisms have changed/evolved over time.

• Fossils of many different

kinds of organisms were

formed in this ancient

lakeshore environment that

existed in Wyoming about

50 million years ago.

IMPORTANT IDEA!!!

The deeper we dig,

the farther back in time we see. (IF the rocks

have not been changed)

Geologic Column- Everywhere in the world we see similarities in fossils.

• Mammals• Reptiles / Dinosaurs• Amphibians• Fish

• Insects• Land Plants

• Primitive Marine Animals• Trilobites

• Single-celled organisms

Life started as just bacteria and evolved from there into the species we see today.

Where would we find fossils most like those alive today? Why?

MASS EXTINCTION

MASS EXTINCTION

MASS EXTINCTION

MASS EXTINCTION

Range of Global Biodiversity PeriodEra

QUATERNARY

TERTIARY

CRETACEOUS

JURASSIC

TRIASSIC

PERMIAN

CARBONIFEROUS

DEVONIAN

SILURIAN

ORDOVICIAN

CAMBRIAN

We can tell from the fossil record that 90% of all species that have lived are now extinct. There have been MANY major extinctions over time.

MASS EXTINCTION

MASS EXTINCTION

MASS EXTINCTION

MASS EXTINCTION

Range of Global Biodiversity PeriodEra

QUATERNARY

TERTIARY

CRETACEOUS

JURASSIC

TRIASSIC

PERMIAN

CARBONIFEROUS

DEVONIAN

SILURIAN

ORDOVICIAN

CAMBRIAN

Why do you think there have been so many extinctions? What can we learn from extinct species?

Why do animals change over time? Why are the animals of today different from the animals of the past?

Index Fossil dating

• Some types of organisms only live for a short period of time. If we know when and how long they lived then if we see fossils of them we know the time period of the rock.

416 to 359 million years ago

540 million years ago 145.5 to 65.5 million years ago

Where is the index fossil?

Find the layer with afossil that only

appears in that one layer

Here it is!!!

***The yellow spiral shell fossil only appears

in this single layer. If we know when this

critter lived, when know exactly when this

layer was deposited! And we can make

estimates of when the layers above and below

were deposited as well!

The layers of strata are numbered along this side

The types of fossilsAre indicated here