Paleontologist: studies life that existed in pre-historic times

Sec FOSSILS Read pages 648 and 649. On your half sheets: 1. What is a FOSSIL? 2. What are some EXAMPLES of fossils? 3. What are 5 ways that fossils FORM?

Fossils and the ways that they Form Section 29.1

Fossil: Any evidence of early life preserved in rock There are 5 basic ways that fossils form:

1. Original remains Bones, teeth Entire animals found frozen in permafrost Insects trapped in tree sap (resin)

Original remains of an insect trapped in the sticky, solidified tree sap (amber)

2. Replaced Remains Soft parts of plants or animals decay leaving a void Groundwater with dissolved minerals (calcite, silica, pyrite) fills the void The result is an exact copy of the original plant or animal Petrified wood: the soft wood decays and is replaced with minerals

3. Molds A leaf, plant, insect or organism is buried in mud or sediment. Leaving a shallow imprint or mold of the original shape. The mud or sediment becomes the rock shale or limestone A hollow depression (mold) of a brachiopod

3. Natural Cast Cast of a trilobite from the Paleozoic Era Minerals seep into a mold and fill-in the shallow imprint A 3-D copy of the original fossil alizations/es2901/es2901page01.cfm?chapter_no=29 Video clip of a mold and cast

4. Trace Fossils Indirect evidence of life, such as a footprint, worm hole, trails, tracks or burrows

5. Carbonaceous Films Sometimes all that is left is a thin carbon film Heat and pressure cause a chemical change in the carbon compounds of the organism

A B C D E

Match the following: a. Leaf print in shale b. Sharks tooth c. Worm holes d. Dinosaur bone e. Petrified wood 1.Original remains 2.Replaced remains 3.Molds / casts 4.Trace fossils 5.Carbonaceous films

Conditions favoring preservation  Rapid burial in soft sediments such as mud that forms shale or sea-floor sediment that forms limestone  Possession of hard body parts such as shells, exoskeletons, bones, teeth

Humans Mammals Dinosaurs Early reptiles Then fish and amphibians First just aquatic creature Principle of Fossil Succession: Living organisms succeed one another in a definite order on the Geologic Time Scale

Fossils and rock dating Principle of Fossil Succession Early organisms lived and went extinct over certain time periods Fossils succeed one another in a definite and determinable order Index fossils Useful in determining the relative age of rock layers The fossil must be widespread geographically Lived and died over a short range of geologic time

Other creatures existed on Earth for hundreds of millions of years before they went extinct. Some organisms lived on Earth a short amount of time (a few millions years) before they went extinct. If we know when they lived, we can use those fossils to help us determine the age of the rock that they died in. Scientists use fossils to determine the ages of rocks Index fossils must be: Unique Plentiful Easily identifiable Occur over large area Lived during a short time span

In which layer of rock strata were Rocks 1, 2 and 3 found? These organisms are unique to a smaller time frame