Chapter 29 Studying the Past

• Paleontology

• Fossils

• Let’s talk about the types………

• The study of life that existed in prehistoric times

• Preserved remains of a plant or animal

• Original remains

• Replaced remains

• Original and unchanged remains of a plant or animal preserved in a rock – Amber is an example (animals caught in sticky tree sap

• Minerals in groundwater replace the decaying plant or animal – like petrified wood!

• Cast

• Mold

• A copy of the original fossil

• A depression in a rock of the original fossil

• Trace fossils • Impressions such as footprints, tracks, burrows or bite marks

Relative Time

• Relative dating

• Strata -

• Placing events in a sequence in which they occurred

• Layers of the Earth

Basics…..

• Law of Superposition • The oldest layers of rock will be on the bottom and the youngest strata or layers will be on top

• Principle of Cross Cutting Relations

• The igneous intrusion that cuts across layers of rock is always younger than the layers it cuts

• Law of Embedded Fragments

• The fossils or fragments of rock that are embedded in a layer are OLDER - because they existed before

• Correlation • The matching of rock layers

• Correlation • The matching of rock layers

• Unconformity • A missing layer in the rock strata

Absolute Time

• Radioactive Decay

• Half-Life

• Radiocarbon Decay – Carbon – 14 dating

• The decay of radioactive isotopes, emitting tiny particles

• The time it takes ½ of a radioactive atoms to decay

• Using the isotope Carbon 14 to date organic material; half life of c-14 is 5,730 years