FossilsFossils

What is a fossilWhat is a fossil

►A fossil is the remains of a living A fossil is the remains of a living organism.organism.

► Includes bones, teeth, hair or shellsIncludes bones, teeth, hair or shells►Can also include impressions, molds or Can also include impressions, molds or

castscasts►Can be a trace fossil, which is evidence Can be a trace fossil, which is evidence

that something was there. Trace fossils that something was there. Trace fossils includeinclude

PoopPoop Footprints

Bird nest

To become a fossilTo become a fossil

►Must die in a wet environmentMust die in a wet environment►Must be buried Must be buried quicklyquickly so the so the

organism is not eaten, decomposed or organism is not eaten, decomposed or weathered.weathered.

►Must have parts capable of being Must have parts capable of being fossilized…hard parts.fossilized…hard parts.

Index FossilsIndex Fossils

►An Index fossil is a fossil used to An Index fossil is a fossil used to

determine the determine the relative agerelative age rocks. rocks.►Relative age is the age compared to Relative age is the age compared to

another rockanother rock It is not the true age of the rockIt is not the true age of the rock It tells you if it is the same age, or if it is It tells you if it is the same age, or if it is

younger or older than another rock.younger or older than another rock.

RequirementsRequirements

►To be an Index fossil, you mustTo be an Index fossil, you must

1. be common (lots of them)1. be common (lots of them)

2. be found in a lot of places worldwide 2. be found in a lot of places worldwide (wide distribution)(wide distribution)

3. exist for a short period of time3. exist for a short period of time

4. Unique. Shouldn’t look like other 4. Unique. Shouldn’t look like other fossils.fossils.

Famous fossilsFamous fossils

► TrilobitesTrilobites

►GraptolitesGraptolites

► AmmonitesAmmonites

Absolute DatingAbsolute Dating

►Tells you the true age of the rock in Tells you the true age of the rock in years.years.

► Is found by looking at radioactive Is found by looking at radioactive atoms in rock.atoms in rock.

► A half life is the time it takes one half A half life is the time it takes one half of the radioactive atoms in the sample of the radioactive atoms in the sample to become non radioactive and turn to become non radioactive and turn into something else.into something else.

How it works.How it works.

►The M&M lab illustrated how it works.The M&M lab illustrated how it works.►All radioactive atoms decay at some All radioactive atoms decay at some

rate. Carbon 14, for example, has a rate. Carbon 14, for example, has a half life of about 6000 years. So it half life of about 6000 years. So it takes 6000 years for half of the atoms takes 6000 years for half of the atoms to decay.to decay.

► If you know how many atoms you If you know how many atoms you started with, and how many you have started with, and how many you have left, you can tell the age of the rock.left, you can tell the age of the rock.

ExampleExample

A rock begins with 1000 carbon 14 atoms A rock begins with 1000 carbon 14 atoms in it. Today it has 250. How old is it?in it. Today it has 250. How old is it?

The half life is 6000 years, so in one half The half life is 6000 years, so in one half life the rock would have 500 carbon 14 life the rock would have 500 carbon 14 atoms.atoms.

In another half life, the rock would go down In another half life, the rock would go down to 250.to 250.

You have 2 half lives, each is 6000 years You have 2 half lives, each is 6000 years so the rock is 12000 years old.so the rock is 12000 years old.