Download GEOLOGIC TIME SCALE

GEOLOGIC
TIME SCALE
***See Earth Science Reference Tables***
GEOLOGIC TIME SCALE:
model of the geologic history of the Earth
(4.5 billion years)
It is mainly based on rock and fossil evidence.
EXAMPLE:
Major group of organisms becomes extinct new time interval
(66 million years age = end of the Mesozoic Era
or beginning of the Cenozoic Era)
Dinosuars became extinct (no more fossils)
GEOLOGIC TIME
The divisions are:
1. EONs
2. ERAs
3. PERIODs
4. EPOCHs
(largest)
(smallest)
None of these are specific amounts of time.
Change when life changes on Earth.
EVOLUTION
Geologists noticed that there are no fossils in the
Precambrian Eon (oldest Eon).
Geologist theorize that:
1. Organisms too difficult to preserve
(very simple organisms with no hard parts)
2. The rocks containing fossils probably have
been destroyed (PLATE TECTONICS) or
altered by metamorphism and weathering
The fossil record is incomplete
(not all the organisms that have lived are fossilized)
Present day organisms more complex than past
CHARLES DARWIN’S:
“THEORY OF EVOLUTION” suggests that
organisms that have characteristics that are
beneficial will survive and pass those traits on
The organisms without these characteristics will
die off
This is known as NATURAL SELECTION
Extinction of some species and the formation of
new ones…