The Geologic Time Table ESRT pg 8&9

Most all divisions on this table are based on life-events that have occurred in the past Eras are divided based upon when dominant life forms existedEras are divided based upon when dominant life forms existed Cenozoic -- "Age of Mammals" Mesozoic -- " Age of Reptiles“ Paleozoic -- " Age of invertebrates" Periods usually begin or end based on a beginning or end of a certain type of animalPeriods usually begin or end based on a beginning or end of a certain type of animal Jurassic Period began when Giant Dinosaurs were abundant.

Eras are the longest period of time on the table. –Usually hundreds of millions of years (except Cenozoic) Periods divide Eras into smaller time periods. Epochs divide periods into smaller time periods.

The Fossil Record A fossil is any evidence of past life –Examples – footprints, original remains of plants/animals, molds & casts

Dunkleosteus (30 ft long; bony skull shown here is about 1 meter high) Extinct at the end of the Devonian

Inferences from fossil evidence 1.Older fossils were simple in structure. As time passed life forms began to increase in size and complexity 2.The types of animals found in a location can indicate the type of climate that animal was living in Coral fossils indicate a tropical climate, marine fossils indicate shallow or deep water environment

Look at ESRT and observe the bottom part of the column under life on Earth. Notice how animals begin as simple cellular animals and eventually change to soft bodied animals, then shells appear, then vertebrates, then reptiles and finally mammals. The process of change that produces new life forms is called EVOLUTION.

Evolution Simply stated, evolution = change.

Index Fossils Index fossils are fossils which existed in a relatively short period of time and over large area Must be easily identified & abundant Useful in marking a period of time If an index fossil is found in a layer of rock, the layer must have been formed in specific period of time

Key Bed A single rock layer that has the same characteristics as an index fossil –Relatively thin, widespread area, deposited rapidly, easy to identify A volcanic eruption can produce a key bed because an eruption happens over a short period of time and usually covers a large area