Transcript The Earth`s Past

Geologic Time Scale
(Earth is 4.6 billion years old)
Geologic Time Scale
 Time scale that outlines the development of Earth and
of life on Earth
 Time scale divisions based on major changes in the
Earth’s surface, climate, or types of organisms
 Time scale divisions usually based on dominant life
forms
Geologic Time Units
 Eon
 Largest unit of time
 4 eons

Hadean, Archean, Proterozoic, & Phanerozoic
 Precambrian time


Hadean + Archean + Proterozoic
Covers about first 4 billion years of the Earth
Geologic Time Units
(continued)
 Eons broken into Eras
 Phanerozoic  Paleozoic, Mesozoic, & Cenozoic
 Eras broken into Periods
 Periods broken into Epochs
 Epochs can be broken into Ages
Geologic Units
Eons
Eras
Periods
Smaller
time units
Epochs
Ages
Eons and Eras
Geologic Columns
 An ordered arrangement of rock layers that is based
on the relative ages of the rocks in which the oldest
rocks are at the bottom
 Layers are distinguished by the type of rock and
types of fossils in the rock
Grand Canyon Geologic Column
Grand Staircase Region
X
X
X
X
X
Precambrian Time
 4.6 Ga (Billion years) – 542 Ma (million years)
 88% of Earth’s history
 Little known about this time
 Rocks are deformed and altered by tectonic activity
Precambrian Rocks & Life
 Rocks
 Shields – large exposed Precambrian rocks
 Nearly ½ of valuable mineral deposits found in shields
 Life
 Very few fossils
 Stromatolites – blue-green algae deposits
Paleozoic Era
 542 Ma – 251 Ma
 Land masses started out apart but ended up together
(Pangaea)
 Rocks have lots of fossils
 Plant & animal species increase dramatically at
beginning of era
 7 Periods
Cambrian Period
 Marine life forms
 Warm shallow seas cover much of the continents
 No evidence of land dwelling plants or animals
Ordovician Period
 Primitive fish
 Lots of invertebrates
 First vertebrates (mostly fish) appear
 No plant life on land
Silurian Period
 Vertebrate and invertebrate marine life dominate
 Land plants & animals evolve near end of period
Devonian Period
 “Age of Fishes”
 Amphibians
 Land plants and seed bearing plants evolve
Carboniferous Period
 Includes Mississippian and Pennsylvanian Periods
 Climate was warm and humid
 Forests and swamps responsible for coal deposits
 Amphibians, fish, large insects
Permian Period
 Appalachian Mountains created
 Shallow inland seas disappear
 Mass extinction
 Many invertebrates die out
 Reptiles & amphibians survive
Mass Extinctions
 Used to indicate end of an era
 Permian mass extinction
 90% of marine organisms
 70% of land organisms
 Plenty of resources for other species to begin to
dominate
Mesozoic Era
 251 Ma – 65.5 Ma
 Pangaea breaks apart to form continents
 Mountain ranges form
 Sierra Nevadas, Andes
 “Age of Reptiles”
 Includes Triassic, Jurassic, & Cretaceous Periods
Triassic Period
 Dinosaurs – mostly 16 feet long
 Reptiles in the oceans
 Ammonites – Mesozoic index fossil
 First mammals appear
Jurassic Period
 Dinosaurs become dominant life form
 2 major groups of dinosaurs
 Saurischians – lizard hipped

Herbivores & Carnivores
 Ornithischians – bird hipped

Herbivores
 Flying reptiles
 First birds
Cretaceous Period
 Dinosaurs still dominate
 T Rex
 Horned and duck-billed dinosaurs
 First flowering plants (angiosperms)
 Magnolias, willows, oaks, maples, walnuts
Cretaceous-Tertiary Mass
Extinction
 C-T Extinction
 End of Cretaceous Period
 No dinosaur fossils found in rocks formed after
Cretaceous Period
 Due to environmental changes from continental
movement or volcanic activity
C-T Extinction (continued)
 Impact hypothesis
 Giant meteorite crashed into the Earth
 Produces dust that blocks the sun
 Planet cools, plant life dies off, animals die off
 Iridium near suspected impact site (Iridium is common
in meteorites, but not Earth rocks
Cenozoic Era
 65.5 Ma to present day
 Continents move to present day position
 Alps and Himalayas form
 Ice ages
 Mammals become dominant
Cenozoic Era (continued)
 Divided into 2 periods
 Tertiary Period

Time before the last Ice Age
 Quaternary Period

From last ice age to present day
 Divided into 7 epochs
Cenozoic Epochs
 Paleocene & Eocene
 Primates evolve
 Whales, flying squirrels, bats
 Still lots of small reptiles
 Worldwide temp drops about 4oC at end of Eocene
Cenozoic Epochs (Continued)
 Oligocene
 Uplifting of Himalayas
 World climate becomes much cooler & drier
 Grasslands favored
 Miocene
 Antarctic ice caps begin to form
 Mediterranean Sea fills and empties several times
 Large land mammals
 Earliest human ancestors(?)
Cenozoic Epochs (Continued)
 Pliocene
 Dramatic climate changes
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


Ice caps grow, water levels fall
Alaska and Russia connected by Bering land bridge
North and South America become connected
Species migrate into different continents
Cenozoic Epochs (Continued)
 Pleistocene
 Ice ages
 Fossils of earliest modern humans
 Holocene
 11500 years ago as last ice age ends
 Sea level rises 140 m
 Great Lakes take their shape
 Humans develop agriculture and begin to use tools