Transcript Geologic Time Notes

EARTH’S HISTORY NOTES
Origin of Planet Earth
Scientists believe
the Earth and the
other planets
formed while the
Sun condensed
from a nebula
Formation of Earth’s
layered structure
As Earth formed
High-velocity impacts caused
Earth’s temps to increase
Iron and nickel sinks towards
the core
Less dense masses of molten
rock produced primitive crust
A early atmosphere was made
mostly of CO2
Life evolves
Earth Cools and oceans form
Bacteria evolve 3.7 BYA
Cyanobacteria produce oxygen
for billions of years!
CO2 in the atmosphere is almost
completely removed and the
amount of oxygen rises.
Geologic Time Scale
is a “calendar” of Earth
history that divides geologic
history into units
•Originally created using
relative dates
Eon– the largest expanses of
time
Era – subdivision of an eon
Periods – Subdivisions of eras
Epochs – are the smallest
timespans
(not to be confused with ewolks!)
Precambrian era (4.5 BYA - 540 MYA)
88% of Earth's history
Precambrian rocks contain
extensive iron ore deposits but
no fossil fuels and few fossils
• (Stromatolites Appear 2 BYA)
Paleozoic era (540248 MYA)
Often called the time of fish
although true fish developed
late in this period.
First life forms Multi-cellular life
forms with hard parts formed
abundant Paleozoic fossils.
Paleozoic era
In the Early Paleozoic life was
restricted to seas, invertebrates
such as
• Trilobites
• Brachiopods
• Cephalopods
First organisms with hard parts,
such as shells - perhaps for
protection
Late Paleozoic era
Supercontinent of Pangaea forms causing
dramatic climate shift
Late Paleozoic
First land plants grow
extensive swamps
forming coal
Insects invade the land
Fishes evolve into two
groups of bony fish
• Lung fish
• Lobe-finned fish which
evolve into the 1st
amphibians
Amphibians diversify
Paleozoic is believed to end as a result of enormous
volcanic eruptions in what is now Russia. These events
poisoned the sea and air and lead to the extinction of
95% of species!
Mesozoic era (248-65 MYA)
Survivors of the great Paleozoic
extinction evolve and diversity.
Gymnosperms (Conifers and ferns)
become the dominant tree
Often called the "age of dinosaurs"
Divided into the Triassic, Jurassic
and Cretaceous Periods
Seas invade western North
America
Mesozoic era
Mesozoic life
Divided into the Triassic,
Jurassic and Cretaceous
Periods
Reptiles - first truly terrestrial
animals readily adapt to the
dry Mesozoic climate with
shell-covered eggs that can
be laid on the land.
Mammals exist only as small
rodent like creatures.
Mesozoic era
Dinosaurs dominate
One group of reptiles
led to the birds
Many reptile groups,
along with many other
animal groups, become
extinct at the close of
the Mesozoic Most
likely the result of a
large asteroid or comet
struck Earth
The Chicxulub Impact Site
Cenozoic era (65 MYA-Present)
Shortest era of geologic time
Mammals diversify & replace
reptiles as the dominant land animal
some groups become very large
(Hornless rhinoceros, stood 16 feet high!)
Angiosperms - flowering plants
dominate the plant world
• Strongly influenced the evolution of
both birds and mammals
• Provide a food source for both birds
and mammals
Cenozoic era
Human Species Evolves
2.5 millions years ago
Homo habilis – early toolmaker
200 thousand years ago –
Homo sapiens
50 thousand years ago
modern humans and large
animals go extinct
12 thousand years ago
development of agriculture and
first cities
250 Million years in a snapshot