Transcript Earth History

Earth History: Geologic Time
Geologic Time
• Geologic Time: It is very, very long.
– Earth is estimated to be around 4.6 billion years
old based on the rock and fossil record.
– Geologic time is broken up into sections based
on major changes in Earth .
Divisions of Geologic Time
Largest Division: Eons
–Eons divided into Eras:
– PreCambrian, Paleozoic, Mesozoic,
Cenozoic
»Ceno - recent
»Meso - middle
»Paleo - ancient
»Zoic - life
»Eras are divided into Periods
PreCambrian
543 million years ago to ~ 4 billion years ago (?)
–“Age of Bacteria”
• Oldest Era
• Longest era because we know so little
about the earth that long ago
• Life: Very little life: only basic forms
including bacteria, the oldest fossils ever
found, seaweed, jellyfish, and worms
– Photosynthesis of the seaweed added
oxygen to the early atmosphere, paving the
way for land life.
First Life
One celled plants
(algae) entered the
fossil record
approximately 3 b.y.
ago (Precambrian).
Large colonies of this
algae are called
stromatolites.
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More Atmospheric Changes
Through
photosynthesis,
O2 was released
into the atmosphere
and ocean allowing
animals to eventually
evolve.
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Paleozoic
543 million years ago to 248 million years ago
• “Age of the Fish”
• Explosion of life in the sea: trilobites,
shellfish, Fish
• Life appears on land: Ferns, Amphibians
• Pangaea formed
• Largest mass extinction ever at the end
of the Paleozoic. 90% of species became
extinct.
Paleozoic
Organisms
Carboniferous Time
In Europe the
Mississippian and
Pennsylvanian periods
are together called the
Carboniferous
period. Vast swamps
and forests from that
time created the huge
coal beds found
throughout eastern
United States.
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Mesozoic
248 mya- 65mya
• “Age of the Reptiles”
• Life: Reptiles are the dominant life on land.
Dinosaurs exist. Birds appear. Forests
of trees appear
• Pangea broke apart during this peroid.
• Dinosaurs become extinct in a mass
extinction at the end of the Mesozoic.
Reptiles:
Appeared in the Permian and quickly
became the dominant life form.
…until Dinosaurs
took over.
They ruled the planet
throughout the
Mesozoic era (the
“Age of Dinosaurs”).
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Birds
Some of the
dinosaurs are
thought to have
evolved into
birds.
Archaeopteryx is
the oldest fossil
bird found to
date.
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Dinosaur Extinction
2. Meteorite
1. Volcanoes
erupt and fill the
atmosphere with
CO2 and gasses
that BLOCK the sun
light preventing
plant life…….
impact causes
multiple natural
disasters
Evidence of a Meteorite
• Layer of Iridium
in rock layers
Cenozoic
65 mya- present
• “Age of the Mammals”
• Life: Large mammals appear, Humans
appear
• Ice Ages occur and ice sheets advance
Mammals
Mammals first appeared in the Mesozoic as small
rodents. After the dinosaurs were erased at the
end of the Mesozoic, Mammals quickly evolved
to become the dominant life form.
The Cenozoic is the “Age of Mammals”. 16
Present
We live in the
Holocene
epoch, of
the
Quaternary
period, of
the
Cenozoic
era.
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