Goal: To understand the
geologic history of the earth.
1) The beginnings of life
2) Life in the ocean
3) Plants onto land
4) Amphibians and Reptiles
5) Dinosaurs!
6) Continents and Supercontinents
7) Age ages and warm periods
8) After the dinosaurs.
When you think about the geologic
history of the earth, what is the part
of geologic history (it can be a time,
event, ect) that sticks out the most
in your mind?
Start of class
• Welcome to 5
billion years ago.
Earth does not
exist yet.
• There is a large
cloud of dust and
gas which will
form the solar
system called a
Giant Molecular
Cloud.
6th minute of class
• 4.6 billion years ago – formation of the earth.
• The cloud of dust and gas creating the sun forms a disc.
• Inside that disc objects clump together making small
meteoroids (10-100k).
• These meteoroids crash into each other. Sometimes
they will break each other apart, but mostly they combine
to make bigger meteoroids.
• Eventually the cores of planets are formed.
• The core materials in the planets depend on where they
form (as it is cooler the further out you go).
• Sometime in this periods an object the size of Mars
crashes into the earth to form the moon.
7.5 minutes of class
(Precambrian Time, Hades Eon)
• The earth has formed. It is 4.5 billion years ago.
• Earth is still molten. Any land formed gets pushed
underneath the surface and is remelted.
• There is probably no life here. The atmosphere is
10-250 bars and is mostly water vapor (50%),
Carbon Dioxide (24%), and Sulfur Dioxide (13%).
The atmosphere comes from volcanoes mostly.
The original atmosphere made of mostly
Hydrogen and Helium is gone.
• The earth is not a pleasant place, and it is being
bombarded constantly by meteorites!
16.5 minutes into class.
(Precambrian Time, Archaean Eon)
• 3.9 billion years ago.
• The bombardment is over. Land starts to form.
• Earliest rocks on earth date back to this period,
but are rare.
• The water in the atmosphere, which has come
from out-gassing volcanoes and impacts from
comets and asteroids, has formed an ocean.
• Carbon dioxide has been dissolved into this rain
water. The atmospheric levels have dropped to
about 1-10 bars, but the atmosphere is now
about 35% Carbon Dioxide and 35% Nitrogen.
• Life has formed!
16.5 minutes into class.
(Precambrian Time, Archaean Eon)
• However, this world is NOT like ours
today!
• The life is single celled organisms in the
oceans (blue-green algae).
• Life is anaerobic – and does not use
oxygen.
• There is very little Oxygen, and almost no
Ozone. The atmosphere would look red.
16.5 minutes into class.
(Precambrian Time, Archaean Eon)
• Also, the land forms are just islands (in
chains).
• There are no continents.
• The earth is very geologically active (lots
of volcanoes).
• The islands over time crash into each
other to form bigger islands. Eventually
this will form the cores of later continents.
22.5 minutes into class.
(Precambrian Time, Archaean Eon)
• 3.5 billion years ago. First fossils (well
microfossils)!
• Soon the earliest continents will form.
• Carbon Dioxide down to 20%, and
Nitrogen is up to 65% of the atmosphere.
36 minutes into class.
(Precambrian Time, end of
Archaean Eon)
• 2.6 billion years ago. Bacterial life makes its
way from the ocean to the land (reef like
structures).
• Atmosphere is still has a lot of Carbon Dioxide
(0.1 bars), but also has a lot of Nitrogen at this
point (80%).
• Continent building is nearing its completion.
85% of the continental mass has been formed
by now.
37.5 minutes into class.
(Precambrian Time, Proterozoic Eon)
• 2.5 billion years ago. Rust bands.
• This shows there was oxygen in the ocean.
• This oxygen immediately would react with the
iron so that the oxygen would not stay in the
ocean, and would not go out of the ocean.
• First supercontinent!
• Oddly enough, climate was COLD! The sun was
probably about 20% less bright at this time.
There is some evidence for large glaciers ON
THE EQUATOR!
Energy transport inside the earth:
• Heat is
continuously
being lost by
the inner core
(so the core
cools with time).
• The outer core
convects.
• So does the
mantel.
• This convection
pushes on the
plates, moving
them.
Supercontinental break up
• If force pushes on part of the supercontinent, it
will be torn apart much like current Africa is (Rift
Valley).
• With time the supercontintent breaks apart, and
all the pieces go in their separate directions.
• Eventually these pieces will collide with each
other forming the next supercontinent.
• When the supercontinent is formed, mountain
ranges are formed as are shallow inland seas.
45 minutes into class.
(Precambrian Time, Proterozoic Eon)
• 2.0 billion years ago. Rust beds.
• Now the Iron in the ocean has all rusted.
• So, the Oxygen goes into the air where it will
react to the Iron in the ground.
• Oxygen is all used up, so does not stay in the
air.
• Carbon Dioxide levels are still at about 0.1 bars
(which would be 300 times higher than today).
• Still cool, but no glacier evidence.
• NOTE: recent evidence is putting the start of
oxygen in the atmosphere back to 2.3 billion
years ago.
46.5 minutes into class.
(Precambrian Time, Proterozoic Eon)
• 1.9 billion years ago.
• Oxygen levels are at 3% (compared to
21% today).
48 minutes into class.
(Precambrian Time, Proterozoic Eon)
• 1.8 billion years ago.
• First Eukaryote fossils.
• Still single celled organisms, but more
complex and bigger.
• Can contain more DNA, and has a
nucleus.
57 minutes into class.
(Precambrian Time, Proterozoic Eon)
• 1.2 billion years ago.
• First multicellular fossils.
• Atmosphere at still 20 to 30 times the
Carbon Dioxide levels of today.
• Oxygen is at 10%, which is half of today.
58.5 minutes into class.
(Precambrian Time, Proterozoic Eon)
• 1.1 billion years ago.
• Rodinia, the 2nd supercontinent formed.
61.5 minutes into class.
(Precambrian Time, Proterozoic Eon)
• 0.9 billion years ago.
• First soft bodied creatures (wormlike
creatures) formed.
• Did they evolve into animals, or is this a
evolutionary dead end?
• Carbon Dioxide is now 10-20 times today’s
levels and Oxygen levels are now closer to
15%.
63.8 minutes into class.
(Precambrian Time, Proterozoic Eon)
• 0.75 billion years ago.
• 4 global ice ages! Each followed by hyper
greenhouse.
• Lots of extinctions.
• “Snowball earth” has ice all the way to the
equator more than likely.
• This lasted for more than 100 million
years.
64.5 minutes into class.
(Precambrian Time, Proterozoic Eon)
• 0.7 billion
years ago.
• Rodinia
breaks up into
the smaller
continents of
Laurentia,
Baltica,
Siberia, and
Gondwana.
66 minutes into class.
(Precambrian Time, Proterozoic Eon)
• 0.6 billion years ago.
• Ozone forms!
• Before this time life can only thrive in the
ocean because deadly solar UV rays pelted
the land.
• Soft bodied creatures diversify and evolve.
67 minutes into class.
(Phanerozoic eon, Paleozoic Era,
Cambrian Period)
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•
•
•
543 million to 488 million years ago.
We are now in the current eon!
At the start is a slight extinction.
A lot of species disappear, but did they die,
evolve, or are we just not getting fossils of
them?
67 minutes into class.
(Phanerozoic eon, Paleozoic Era,
Cambrian Period)
• There were large shallow seas – ripe conditions
for life.
• So, there was an explosion of evolution during
this time period.
• All the types – or phyla – of animals were created
here including vertebrates.
• Climate was warm and stable as Carbon Dioxide
levels went back up to 10-20 times the levels of
today.
• At the end of this Period the next supercontinent –
Gondwana – forms.
• However, still nothing on land (other than bacteria
close to shores)!
67 minutes into class.
(Paleozoic Era, Ordovician Period)
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•
•
•
•
488 to 433 million years ago.
First fish and land plants develop.
At end of period, first sharks.
Gondwana drifts to the South Pole.
The end is marked
by a giant ice age
which kills off 50%
of all plant life and
25% of the animal
life in the sea.
69 minutes into class.
(Paleozoic Era, Devonian Period)
• 420 to 350 million years ago.
• Explosion of land plants and oxygen reaches modern
levels.
• Arthropods (including insects and spiders) start to live on
land.
• First 4 legged fish evolve (tetrapods) and soon become
Amphibians.
• Carbon dioxide levels drop from 15X today to 5X today.
• 364 million years ago – extinction!
• Life on land not much affected.
• > 50% of marine species go extinct.
• First seed plants and first forests.
• At end of Devonian Period, you have the start of reptiles!
71 minutes into class.
(Paleozoic Era, Permian Period)
• 300 to 250 million years ago.
• First mammal like reptiles!
• Period starts with temperatures and Carbon Dioxide levels
similar to today.
• The supercontinent
Pangaea forms.
71 minutes into class.
(Paleozoic Era, Permian Period)
• Paleozoic Era ends with a HUGE extinction event
(actually 2 pulses separated by 8 million years)!
• 90-95% of marine species and 70% of land
species went extinct!
• Largest known extinction!
• While cause is unknown (volcanic, to meteorite
impact, to nearby supernova), what is known is
that Carbon Dioxide levels shot up by a factor of 6
and global temperatures went up by 11 C or 20 F.
• Only mass extinction for insects.
• Most plant life disappears.
71.7 minutes into class.
(Mesozoic Era, Triassic Period)
• 220 million years ago.
• First mammals (small), first dinosaurs (small), first
crocodiles, and first flying reptiles.
• Temperatures are warm and dry with cold winters.
• No polar glaciers.
• At 210 million years ago there is a lot of volcanic
activity, Pangaea starts to rift and huge, and
global temperatures go down.
• This is followed by extinctions of most marine
reptiles and many other species (50%) as did
many land reptiles and some primitive dinosaurs.
72.8 minutes into class.
(Mesozoic Era, Jurassic Period)
72.8 minutes into class.
(Mesozoic Era, Jurassic Period)
• 200 million to 148 million years ago.
• Climate more moist
• Allosaurus, Brachiosaurus (largest known
dinosaur), Diplodocus, Pterodactylus, and
Stegosaurus all lived during this period.
• Atlantic Ocean starts.
• First small birds.
72.8 to 74 minutes into class.
(Mesozoic Era, Cretaceous Period)
• 148 million to 65 million years ago.
• Climate very warm. No polar ice. High sea
levels. Shallow seas.
• Deep ocean 15-20 C warmer than today!
Therefore, warmer much farther from equator
than before.
• First flowering plants.
• Ankylosaurus
• Triceratops
• Tyrannosaurus Rex
• Velociraptor
74 minutes into class
• 65 million years ago
• A 10 km asteroid (maybe comet) strikes
the earth of the coast of the Yucatan
peninsula.
• Shortly after 70% of all species go extinct
including most of the dinosaurs.
• The meteor crater has been discovered.
• What exactly is the impact like?
• (big long speech here)
Lets watch the continents!
• http://ircamera.as.arizona.edu/NatSci102/
NatSci102/lectures/earth.htm
74 to 74.2 minutes into class.
(Cenozoic Era, Paleogene Period, Paleocene Epoch)
• 65 to 56 million years ago
• Birds ruled the world!
• Huge birds which could no longer fly
dominated the ground.
• 60 million years ago – first primates.
• 57 million years ago – first rodents
• Demise of birds: got too large, so had to
nest on the ground where their eggs were
devoured by insects.
74.2 to 74.5 minutes into class.
(Cenozoic Era, Paleogene Period, Eocene Epoch)
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•
•
•
56 to 33 million years ago
Mammals take over.
First whales and horses.
Climate starts to dry and cool. Carbon
dioxide levels fall from 3X today to about
today’s levels.
• Cooling triggers a global extinction
especially at higher latitudes.
• Forests become more open.
74:39.3 to 74:55.7 minutes into class.
(Cenozoic Era, Neogene Period, Milocene Epoch)
• 23 to 5.3 million years ago
• 25 million years ago – Ape/Human line evolves.
• First grasses – more adapted to cool, dry
climates.
• 21-14 million years ago, warming, then sudden
drop with a 2nd drop 8 million years ago.
• Oceans cool.
• 20-10 million years ago Cascades, Andes, and
Himalayas form.
• 6 million years ago Chimpanzees separate from
hominids.
74:55.7 to 74:58.38 minutes into class.
(Cenozoic Era, Neogene Period, Pliocene Epoch)
• 5.3 to 1.8 million years ago
• 3 million years ago, permanent ice sheets
in Antarctica.
• 2 million years ago – start of global ice
ages!
74:58.38 to 74:59.99 minutes into class.
(Cenozoic Era, Quaternary Period, Pleistocene Epoch)
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•
•
1.8 million to 12k years ago.
Ice ages have glaciers progress then retreat.
600k years ago – early humans.
100k years ago – first Homo Sapiens
30k years ago Neanderthal goes extinct.
End of Pleistocene – Wooly Mammoth,
Sabertooth Tiger, Mastodons, Cro-Magnon, and
a lot of other species go extinct – end of last ice
age.
Conclusion
• The earth has changed a LOT during its history.
• Many factors influence a planet’s climate.
• Life if greatly influenced by a planet’s climate,
but can be affected by other external factors.
• As we head into the future, we will see many of
the conditions for climate in the past re-emerge,
and we must adapt to them or become another
statistic on the timeline of the history of the
earth.