Life Science

Indicator S.HS.4.2.1

Part A

Life Science

Indicator S.HS.4.2.1

Part A

The student understands geological

time is used to understand the Earth’s

past.

The Geologic Time Scale

notice these points….

1. the timeline is approximately 4.5 billion years….the current accepted age of the Earth

2. there are 4 eras3. the oldest and the longest era is the

Precambrian….approximately 4 billion yrs4. the last 3 eras are approximately ½ billion

years combined, or 500 million years (much shorter)

Did you notice the proportional size

differences of each era!

88% of the time is Precambrian

{

and these points…..

1. the rocks formed during the Precambrian have very few fossils ….. not much life existed back then

2. stromatolites and blue-green algae

Stromatolites are mounds of prokaryotic algae and cyanobacteria.

Look at the next slide and notice…..

When (how long ago) does abundant life begin to show up

in the rock record?

600 million years ago or the beginning of the Phanerozoic

1. the Phanerozoic means “visible life” – it is an eon made up of 3 eras

A. paleozoic – “ancient life”

B. mesozoic – “middle” life

C. cenozoic – “recent” life

Key points….

• the geologic time periods are based on major geologic events that took place

A. mass extinctions

B. glaciation periods

C. climate changes

Extinction events

Glacial event

The Earth has changed over time!

1. Short term changes (occur during a human’s lifetime)

a) earthquakes – change the surface of the land

b) volcanic eruptions

2. Long term changes (long time for them to occur)

a) erosion – the Grand Canyon

b) mountain building – the Rockies

Earth’s atmosphere has changed over time!

1. original atmosphere look like the gas that comes out of volcanoes

a) water vaporb) carbon dioxidec) nitrogend) NO OXYGEN

2. oxygen begins to accumulate in the atmosphere about 2.5 billion years ago

a) primitive organisms used photosynthesis - algae

Radioactive Dating

• a method for age dating rocks/fossils• radiometric dating – rocks• radiocarbon dating – fossils• parent to daughter ratio tells us how old

the rock/fossil is• radioactive dating allows us to assign

dates to specific rock layers

Kansas has sedimentary rock like limestone or halite (rock salt)

both are formed in shallow seas

Kansas was under water at least 4 times in history…the last was during the Cretaceous period