FOSSILS

What is a fossil?

• Remains of once living animals or plants

• Represent ancestors of organisms living today

Does every organism turn into a fossil?

• No - Normally they rot or get eaten• If the conditions are correct they can be

buried quickly and fossilized– 5 Different steps

How are fossils formed?1. Animal dies and is buried by sediment2. Extreme pressure turns sediment into stone3. Skeleton dissolves and leaves a hole/mold– Dissolved by ground water

4. Minerals crystallize in hole and a cast is formed– Mineral rich water enters mold and leaves minerals

5. Millions of years later, the fossil is exposed on the Earths surface– Earthquakes, mountain building, construction, digging/drilling

What do fossils tell us?• How plants and animals used to live– Individual? Group?

• Where plants and animals used to live• How plants and animals from the past are related

to the ones today• How plants and animals develop• What type of animals/plants used to be present

What different types of fossils are there?

• Body fossils – Tell us what the animal/plant

looked like– Ex: Petrified wood, frozen

mammoths, amber• Trace fossils– Tell us what the animal did– Ex. Footprints, trackways,

Coprolites (poo)

How do we get information about fossils?

• Relative dating– Rock Layers

• Absolute dating– Radioactive Half-Life

How are rock layers formed?

• Rocks are…– Melted– Cooled– Weathered/ Eroded– Compacted/ Cemented– Heated/ Pressurized

How are rock layers formed?

Rock layers = Sedimentary Rocks– Formed when particles are

deposited on top of other particles

– Pressure pushes down– Dissolved minerals form natural

glue– Creates rocks at or near the

surface

Why are rock layers important?• Tell our history• Geologic Column– Ideal sequence of rock layers that contain known

fossils and rock formations. – Arranged from oldest to youngest

• Gaps in history– Erosion– Natural events – Folding, Faults,

Volcanoes

What do the rock layers tell us?• When events happened– In general rocks in the same layer happened

at the same time• Fossils in the same layer lived at the same time

What is radioactive decay?• Certain naturally occurring elements are

radioactive and they break down at predictable rates

• Scientists measure the half-life of elements– Half life = the time it takes for half the radioactive

element to break down• Scientists compare the amount of an element to

the initial amount and the half-life to determine age

Why is radioactive decay helpful?

• Also called carbon dating• Allows us to calculate an age• Cannot be used for objects older than 70,000 years