The Geologic Time The Geologic Time TableTable

ESRT pg 8&9ESRT pg 8&9

Most all divisions on this table Most all divisions on this table are based on life-events that are based on life-events that

have occurred in the pasthave occurred in the past • Eras are divided based upon when Eras are divided based upon when

dominant life forms existeddominant life forms existedCenozoic -- "Age of Mammals"Mesozoic -- " Age of Reptiles“Paleozoic -- " Age of invertebrates"

 • Periods usually begin or end based on a Periods usually begin or end based on a

beginning or end of a certain type of beginning or end of a certain type of animalanimal

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 The Fossil RecordRecord

• A fossil is any evidence of past life– Examples – footprints, original remains

of plants/animals, molds & casts

http://www.stonecompany.com/fossils/invertebrates/crustaceans/crabs/solnhofen/images/crabDSC03440z.jpg

Dunkleosteus (30 ft long; bony skull shown here is about 1 meter high)

Extinct at the end of the Devonian

Inferences from fossil Inferences from fossil evidenceevidence

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.

EvolutionEvolution

Simply stated, Simply stated, evolution = change.evolution = change.

VIF!!!! - Index VIF!!!! - Index FossilsFossils • Index fossils are fossils that have the

following characteristics:– existed in a relatively short period of

time – existed over a large geographic area– Must be easily identified & abundant

• They are useful in determining a period of geologic time within rock layers.

• If an index fossil is found in a layer of rock, the layer must have been formed in that index fossil’s specific period of existence.

Key BedKey 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

• A meteor strike can also produce a good key bed due to all of the debris that it scatters into the atmosphere.