Fossils

What is a fossil ► A fossil is the remains of a living organism. ► Includes bones, teeth, hair or shells ► Can also include impressions, molds or casts ► Can be a trace fossil, which is evidence that something was there. Trace fossils include

PoopFootprints Bird nest

To become a fossil ► Must die in a wet environment ► Must be buried quickly so the organism is not eaten, decomposed or weathered. ► Must have parts capable of being fossilized…hard parts.

Index Fossils ► An Index fossil is a fossil used to determine the relative age rocks. ► Relative age is the age compared to another rock  It is not the true age of the rock  It tells you if it is the same age, or if it is younger or older than another rock.

Requirements ► To be an Index fossil, you must 1. be common (lots of them) 2. be found in a lot of places worldwide (wide distribution) 3. exist for a short period of time 4. Unique. Shouldn’t look like other fossils.

Famous fossils ► Trilobites ► Graptolites ► Ammonites

Absolute Dating ► Tells you the true age of the rock in years. ► Is found by looking at radioactive atoms in rock. ► A half life is the time it takes one half of the radioactive atoms in the sample to become non radioactive and turn into something else.

How it works. ► The M&M lab illustrated how it works. ► All radioactive atoms decay at some rate. Carbon 14, for example, has a half life of about 6000 years. So it takes 6000 years for half of the atoms to decay. ► If you know how many atoms you started with, and how many you have left, you can tell the age of the rock.

Example A rock begins with 1000 carbon 14 atoms in it. Today it has 250. How old is it? The half life is 6000 years, so in one half life the rock would have 500 carbon 14 atoms. In another half life, the rock would go down to 250. You have 2 half lives, each is 6000 years so the rock is years old.