Transcript Life Science

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 eras
3. the oldest and the longest era is the
Precambrian….approximately 4 billion yrs
4. 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)
b)
c)
d)
water vapor
carbon dioxide
nitrogen
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