Earth History: 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,
»Ceno - recent
»Meso - middle
»Paleo - ancient
»Zoic - life
»Eras are divided into Periods
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.
One celled plants
(algae) entered the
approximately 3 b.y.
Large colonies of this
algae are called
More Atmospheric Changes
O2 was released
into the atmosphere
and ocean allowing
animals to eventually
543 million years ago to 248 million years ago
• “Age of the Fish”
• Explosion of life in the sea: trilobites,
• Life appears on land: Ferns, Amphibians
• Pangaea formed
• Largest mass extinction ever at the end
of the Paleozoic. 90% of species became
In Europe the
are together called the
period. Vast swamps
and forests from that
time created the huge
coal beds found
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.
Appeared in the Permian and quickly
Reptiles: became the dominant life form.
They ruled the planet
Mesozoic era (the
“Age of Dinosaurs”). 11
Some of the
thought to have
the oldest fossil
bird found to
1. Volcanoes 2. Meteorite
erupt and fill the impact causes
CO2 and gasses multiple natural
that BLOCK the sun disasters
Evidence of a Meteorite
• Layer of Iridium
in rock layers
65 mya- present
• “Age of the Mammals”
• Life: Large mammals appear, Humans
• Ice Ages occur and ice sheets advance
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
We live in the