Unit 1: History of the Earth Living or non-living everything has a history Earth has a history We are fortunate to live in a time when we can study the Earth’s history

What are Fossils? Remains, imprints, or traces of once-living organisms preserved in rocks Presentation ShellSpider, Beetle…Alien? Fish

Why Study Fossils? Helps scientists determine approximately: WHAT the living thing looked like WHEN … Life began Plants and animals first lived on land Certain types of organisms disappeared HOW they lived

Necessary Conditions 1. The body of the dead organism must be protected from scavengers and microorganisms e.g. Being buried quickly by sediments, flood-like or wind storm conditions 2. Organisms have a better chance of being preserved if they have hard parts e.g. Bones, shells, or teeth But, I don’t want to be a fossil.

Types of Fossils 1. Petrified Remains 2. Carbonaceous Films 3. Molds and Casts 4. Original Remains 5. Trace Fossils 6. Index Fossils But, I really don’t want to be a fossil.

1. Petrified Remains  Hard, rocklike  Some or all of the original materials in the remains have been replaced by minerals  We learn about past life-forms from bones, wood, and other remains that become petrified

2. Carbonaceous Films When all that’s left is a thin film of carbon residue from the original organism, forming an outline The main element that makes up all living things is carbon We are “Carbon based life forms”

3. Molds and Casts Like impressions of plaster of paris In nature, such impressions are made when seashells and other hard parts fall into soft sediment and are buried Cast Mold

Mold and Casts: How they form i.A living thing dies and/or is quickly trapped under sediments ii.Sediments turn to rock; organism is impressed into the rock material iii.Organism dissolves and is removed from rock layers, leaving behind a mold iv.Minerals or rock material fill the mold and hardens, creating a cast of the original creature.

4. Original Remains Not quite an official fossil When the actual organism or parts are found preserved in some other substance Such as: ice, tar, amber

5. Trace Fossils Fossilized tracks and other evidence of animal activity

6. Index Fossils From species that: 1. Existed on Earth for relatively short periods of time, 2. Were abundant, 3. Were wide-spread geographically Index fossils “mark” a specific layer in rocks Shells make good index fossils