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Chapter 9 A View of the Earths Past
Section 1. Geologic Time
The scale outlines the development of Earth and life on
Earth. It is the summary of major events in Earth’s past that
are preserved in the rock record. Fossils are an important
part of this scale.
Geologic Column
No single rock layer on Earth contains a record of all of the
geologic events, so scientists combine their observations to
create standard arrangement of rock layers.
Using a Geologic Column
Scientists use the rock layers to date rock layers that can not
be dated radio metrically. They compare fossils in similar
rock layers or that is relatively the same time period. If they
match, than the rocks were likely formed around the same
time.
Division of Geologic Time
It is usually broken down by fossils of a dominate life form.
Eons and Era’s
Eons – Longest segment of time
Haden and Achaean Eon*
4.6 billion years ago to 2.5 billion
Earths formation to first fossils
Proterzoic Eon*
2.5 billion years ago to 570 million
No life on land
Fossils of simple plants & animals
* Also called Precambrian Eon
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Phanerozic Eon
About 570 to present
Era- a long period of time that is further divided
Paleozoic Era
Age of Invertebrates
543 million years ago
Mesozoic Era
Age of Reptiles
248 million years ago
Cenozoic Era
Age of Mammals
65 million years ago to present
Periods and Epochs
Period – are a shorter period of time further divided
usually named for the place where a fossil was found.
Cambrian
543 million years ago
Ordovician
490 million years ago
Silurian
443 million years ago
Devonian
417 million years ago
Carboniferous
Mississippian 354 million years ago
Pennsylvanian 323 million years ago
Permian
290 million years ago
Triassic
248 million years ago
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Jurassic
206 million years ago
Cretaceous
144 million years ago
Tertiary
Paleocene 65 million years ago
Neocene 24 million years ago
Quaternary
2 million years ago to present
Epochs – the next smallest time division
Early, Middle & Late
Cenozoic Era is the only one with names
Paleocene 65 million years ago
Eocene 54.8 million years ago
Oligocene 33.7 million years ago
Miocene 24 million years ago
Pliocene 5 million years ago
Pleistocene about 2 million
Holocene started about 10 thousand years
ago to present
Age- even a smaller division – usually a new fossil was
introduced.
Section 2 Precambrian Time and the Paleozoic Era
Evolution
The process of change that produces new life forms
Charles Darwin (1859)
Proposed:
Surviving offspring inherited favorable traits to
further survive the environment
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An organism adapts to the environment or
becomes extinct
Natural Selection which is the processes that
allows animals and plants that are best suited
to survive to reproduce and pass on their
traits
Time can create new species
Species – a group of organisms that can reproduce fertile
offspring
There is tremendous amount of debate over whether the
changes in evolution take place quickly or if they are slow
and steady. The best scientific evidence now points to
Punctuated Equilibrium. Which involves a slow natural
process then some kind of change happens to the
environment and there is a series of very rapid changes or
Bursts of Evolution.
Precambrian Life
It is the time period from 4.6 billion to 542 million years ago.
This includes about 88% of Earth’s history occurred during
this time. The rock record has been deformed so much that
scientists can not interpret what took place and when it took
place.
Precambrian Rocks
Shields – large areas of Precambrian exposed rocks
Precambrian Life
Very little life has been discovered. The life forms that
were mostly found were cyanobactria in stromatolites or
layered reef like deposits.