GEOLOGICAL TIME SCALE
Geological Time Scale
*
A
record of the life forms and geologic events in Earth’s history.
*
Scientists
placed Earth’s rocks in order by relative age to create the geologic column.
*
We
developed the scale by studying these rock layers and index fossils.
*
Radioactive
dating helped us determine the absolute date of the divisions in the scale.
Divisions of Geological Time
Scale
*
As
they studied the fossil record, they found major changes in life forms at
certaintimes.
*
They
used these changes to mark where one unit of geologic time ends and the next
*
begins.
*
Divisions
of the geologic time scale depend on events in the history of life on Earth.
Divisions Of Time
1. EON –
largest division of geologic time
2. ERA –
2nd largest, includes two or more periods
3. PERIOD –
3rd largest, unit into which eras are divided
4. EPOCH –
4th largest, the subdivision of a period
EON
> ERA > PERIOD > EPOCH
EONS DIVISION
1. Hadean –
rocks from meteorites and moon
2.Archean –
earliest rocks on earth form
3.
Proterozoic – organisms with well developed cells
4.
Phanerozoic – means “visible life” well represented in the fossil record
ERAS DIVISION
A.Paleozoic
–“earlylife” 544 - 244mya
B.Mesozoic
–“middlelife” 245 -66mya
C.Cenozoic
–“recentlife” 66mya -present
PERIODS DIVISION
Cambrian – Explosion of
life
Ordovician – 1st Vertebrate
Silurian – 1st Land
Plants
Devonian – Age of Fish
Mississippian – Winged
insects
Pennsylvanian – First
reptiles
Permian – Age of
Amphibians
Triassic – First
Dinosaurs/Small mammals
Jurassic – First
Birds/Flowering Plants
Cretaceous – Heyday of
Dinosaurs
Tertiary – Mammals
Thrive
Quaternary – Age of
Man/Technology
The Earth Through Time
The
Proterozoic:
§ No life possible as the Earth initially forms 4.6
billionyears ago.
§ Simple, single-celled forms of life appear 3.8 billion
years ago, Land masses gather to make up a continent called“Rodinia”
Cambrian:
•
Explosion of life
•
All existing phyla come into being
at this time
•
Life forms in warm seas as oxygen
levels rise enough to support life
•
Dominant animals: Marine
invertebrates
•
Supercontinent Gondwana forms near
the South Pole (note position of present- day Florida)
Ordovician:
•
The 1st animals with bones appear,
though dominant animals are still trilobites, brachiopods and corals
•
Four
main continents: Gondwana, Baltica, Siberia and Laurentia
Silurian:
•
First land plants appear and land
animals follow
•
Laurentia collides with Baltica and
closes Iapetus Sea.
Devonian (Age of the Fish)
•
Pre-Pangea forms. Dominant animal:
fish
•
Present-day Arctic Canada was at
the equator and hardwoods began to grow.
•
Amphibians, evergreens and ferns
appear
Mississipians
•
First seed plants appear
Pennsylvanian:
•
Modern North America begins to form
•
Lizards and winged insects first
appear.
Permian:
•
Pangea forms. Reptiles spread
across continents.
•
The Appalachians rise 90% of
Earth’s species become extinct due to volcanism in Siberia.
Triassic:
•
First dinosaurs appear
•
First turtle fossil
•
Pangea breaks apart
Jurassic:
•
Pangea still breaking apart
•
Dinosaurs flourish “Gold of
dinosaurs”
•
First birds appear
•
North America continues to rotate
away from Africa
Cretaceous:
•
First
snakes and primates appear
•
Deciduous
trees and grasses common
•
First
flowering plants
•
Mass
extinction
Tertiary:
•
First horses appear and tropical
plants dominate (Paleocene)
•
Grasses spread and whales, rhinos,
elephants and other large mammals develop
•
Dogs, cats, and apes appear
(Oligocene)
Quaternary:
•
Modern humans develop and ice
sheets are predominant- Ice age (Pleistocene)
•
Holocene Humans
•
flourish (Holocene)
******************************************************************************
sayantani singh MSC GEOGRAPHY B.ED)
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