earth Science
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Oct7_Geological_time.pptxExploring Geologic Time: Millions, Billions…. whatever
Present
Earth forms
Chapter 23.3 – 23.8 in text
The stages of earth’s history have names.
The 4.6 billion years of Earth’s history can be divided into 2 major time segments called eons.
Precambrian 4600 Ma to 550 Ma
Phanerozoic 550 Ma to present
“zoic” means “life” in Greek. Like “Zoology”
Ma means million of years ago
The story of the earth
The following few slides are artist conceptions of the
early Earth. We don’t know exactly what it looked like,
But we have an idea
In the beginning
4 ½ billion years ago: beginning of
Pre-Cambrian Eon
Igneous rocks beginning to crystallize
About 4 billion years ago. Atmosphere starting to form from gas from
volcanos (but its totally poisonous). Icy comets deliver the H2O?
After more cooling: Liquid water and rain can exist
Oceans have formed at about 3.5 billion years before present.
Microbial life probably formed quickly around this time
Eon
Continents were very different
Continents move continuously: Continental Drift
On our timeline
Oceans form. First evidence
for fossil life found
Oxygen builds up in atmosphere
From photosynthesis
First animals, multicellular life
From About 0.55-3 billion years ago
Most of Earth’s history looked something like this
Mats of primitive
algae coating the
rocks
These plants started
producing oxygen.
Our atmosphere
Slowly becomes more
breathable
Fossils from the Precambrian Eon (rare)
Trace fossils of early animals: that’s all there are
Animals did not have bones or shells
We don’t really know what this
is but it may be related to modern
starfish
Precambrian Eon
Large fraction of Earth’s history (how large?- wait)
intense volcanic activity; oceans form; meteorite bombardment
atmosphere develops from primitive life through out-gases from volcanoes to one with free oxygen
life begins with unicellular organisms (blue-green algae and bacteria) and evolves to multi-cell organisms like worms
few fossils exist because most did not have hard parts
The Phanerozoic Eon is divided into time segments called eras.
Paleozoic (“old life”) 550 Ma to 245 Ma
Mesozoic (“middle life”) 245 Ma to 66.4 Ma
Cenozoic (“recent life”) 66.4 Ma to present
The Paleozoic and the Mesozoic both ended with mass
extinctions which allowed new life forms to take over
Beginning of Paleozoic Era: the Cambrian Explosion
To understand “explosion”, think of principle of superposition
No fossils here
Lots of fossils here
This sudden jump is seen around the world
Beginning of Paleozoic Era: the Cambrian Explosion
Suddenly an enormous diversity of animal fossils are seen.
Likely reasons:
1. Enough oxygen was now present for animals to grow
2. Animals acquired hard shells so are better preserved
Trilobite
Middle of Paleozoic Era
Plants move onto land first followed by insects and air breathing
fish with primitive legs amphibians
End of Paleozoic Era: Pangea
Collision of continents leads to mountain building
Pangea (Greek for “all lands”) was a “supercontinent”
What happened when Europe collided with North America?
Sideling Hill syncline. Formation of Appalachian Mts.
The Paleozoic Era
Ends with formation of Pangaea
Life moves onto land for the first time. Plants first, then animals
appearance of fish, insects, amphibians, and some reptiles huge increase in number of fossils because hard shells/bones evolved which are more
easily preserved
The Permian mass extinction
95% of ocean life wiped out.
70% of land life
Probable cause- earth got too hot.
Ocean temps jumped up to about 90F
Why- lots of volcanic activity spewed CO2. When dissolved in
ocean water, made oceans too acidic. Worse than anything
we are likely to do with global warming
Why so many volcanoes? Formation of Pangea with all the
converging plates? Formation of Pangea eliminated many
coastline with rich ecosystems (no one is sure)
Continental Drift
End of Mesozoic
Pangea broken
up. Modern continents
formed, but not in present
positions.
Beginning of Mesozoic
continents all
together as Pangea
Mesozoic Era Dinosaurs
Beginning: Triassic
Recover from the mass extinction
reptiles expand first dinosaurs
mammals evolve
N. Atlantic ocean begins to form- N. America separates
The big dinosaurs
Birds evolve from dinosaurs.
Middle: Jurassic
The first bird
Early birds in Mesozoic era had teeth and claws on the ends of
their wings
Cretaceous
Pangea fully broken up- Atlantic Ocean mostly formed
Flowering plants- modern trees.
A spectacular ending
As imagined from the surface
As imagined from space
They think they found the crater (because of sediment deposition, its hard to find)
Summary: The Mesozoic Era
known as age of reptiles; dinosaurs are prominent lifeforms; birds evolve
3 periods: Triassic, Jurassic, Cretaceous
last part of Cretaceous witnesses large-scale extinction of marine and flying reptiles as well as dinosaurs; extinction may be due to massive asteroid collision with Earth
Pangea breaks up: modern continents form
The Cenozoic Era
Big reptiles are dead age of mammals
climates cool generating Ice Age at the end
Why?
Favorite theory has to do with where the continents were. What differences from present do you see?
Difference #1: N. America is disconnected from S. America
Atlantic Ocean is connected to Pacific
Consequence: Tropical waters of Pacific can flow into Atlantic
and keep Atlantic hotter than at present. When N. America
connects to S. America this warming effect stops
cooler
Warm water
blocked
Difference #2: India crashes into Asia. Converging plates
make worlds highest mountains.
Consequence: Warm winds from Indian Ocean can’t get past
this mountain range. Northern Asia gets colder
colder
Warm winds
blocked
Combined effects: Winters in N. Atlantic and Northern Asia get
much colder snow and ice can build up
Late in the Cenozoic Era
Some apes start walking upright and using tools
Artist conception
Reconstructed from
Skull fossils
Footprint looks human
About 1
Million years
ago
vocabulary
What happened in the
Precambrian Eon
Phanerzoic Eon
Paleozoic Era. (Begins with Cambrian Period
ends with Permian mass extinction)
Mesozoic Era (Triassic,Jurassic and
Cretaceous Periods)
Cenozoic Era
OK, fine. Back to Billions, millions, whatever………….
Need a sense of proportion (or context, or perspective)
For what percentage of earth’s history has life been present?
Ans: 3.5 out of 4.6 billion year (3.5/4.6 x 100 = 76%)
More in depth
What percentage of earth’s history before animals developed
hard shells/bones?
Answer: Precambrian ended 550 million years ago
1. Convert earth’s age to 4,600 million years
2. Subtract 4600-550 = 4050 million years. Earth was already
4050 million years old before bones developed!
3. Divide 4050/4600 = .88 88% of earth’s history
Relate to other time scales
If we shrunk all of earth’s history to 1 year, when would
hard shells/bones develop?
Ans 88% of 12 months = 0.88 x 12 = 10 1/2 months
mid November
If we shrunk all of earth’s history to 1 day, when (i.e what time)
would hard shells/bones develop?
Ans: 88% of 24 hours is = 0.88 x 24 = 21.1 hours
just after 9 pm
Expand the scale for Phanerozoic the last small fraction of earth’s history
Paleozoic Era
Mesozoic Era
Cenozoic
Era
cretaceous
jurassic
triassic
Permian mass
extinction
Asteroid kills
dinosaurs
Cambrian
Explosion of
Hard shell
fossils
Ice age,
humans
Another question
If we shrank earth’s history to 1 year, when did humans show up?
First- 1 million years ago is how many billions.?
1 million/1 billion is .001 = 1E-3
Then 1E-3 billions/4.6 billions = .00022 = .022 %
is the amount of earth’s history humans have been present
So how much of earth’s history happened before humans?
1.0 - .00022 = .99978 or 99.978%
What is .99978 of a year x 365 days = 364.92 days
last day of the year and 0.92 days is about 22 hours
So 2 hours before midnight on New Years Eve
Humans are very late to the party!
Continuing
If 1 million years shrinks to 2 HOURS, all of HUMAN history
from Ancient Babylonia (say 10,000 years ago)
to now comes to about 1 minute
year. Everything we know is just an instant in geological time!
And the distant future- 50 thousand years from now is merely
one more minute compared to a year of geologic time
General approach:
1. Make sure you have the time units correct (millions, billions)
4.6 billion years = 4600 million years
2. a. If working backwards (i.e. millions of years ago), need to
subtract 1 – time in question = get earth’s age when
something happened)
(see example with hard shells 4600-550 = 4050 million years old)
b. if working forwards (i.e. it took 4.050 billion years to get bones)
then 4.050/4.6 = 88% of earth’s history
3. Pay attention to what scale you’re using (compressing earth’s
history to 1 year or 1 day). We could use a length- i.e. a 1 meter
ruler. So out of 1 meter, humans came along with less than a millimeter towards the end.
Final summary:
Make sure you know the relative lengths of time and how
to compare to more familiar scales
