Transcript Earth`s History

Earth’s History
Origin of the Earth
• Nebular Hypothesis
– Bodies of our solar system condensed from
an enormous cloud
– Cloud began contracting, spinning, and
flattening
• Earth
– Density sorted material and eventually, gases
escaped from the interior to form an
atmosphere
Earth’s Atmosphere Evolves
• Outgassing
– Gases that are in molten rock are gradually
released
• Water vapor condensed to form clouds
– Rain cooled Earth’s crust until the rains slowly
filled low areas, forming the oceans
– Reduced CO2 because it became trapped in
water
• Plants evolved and released oxygen
Precambrian Time
• 4.6 billion to 570 million years ago
• Precambrian Rocks
– Shields
• Areas shaped like shields that have been
extensively eroded to reveal Precambrian rock
• Mostly deformed metamorphic rock
• Ore deposits
Precambrian Time
• Precambrian Fossils
– Stromatolites
• Calcium carbonate deposited by algae
• Indirect evidence of algae
– Tiny organisms
• Life 3.5 billion years ago
• Most preserved in chert, a hard, dense chemical
sedimentary rock
– Prokaryotes found (blue-green algae & bacteria)
• Southern Africa—3.1 billion years
• Lake Superior—1.7 billion years
Precambrian Time
– Eukaryotes found (green algae)
• Bitter Springs, Australia—1 billion years
– Plant fossils date from the middle
Precambrian
– Trace fossils of animals
• Trails and worm holes
• Fossil impressions
– Animal fossils date from the late Precambrian
– Diverse and multicelled organisms exist by
the close of the Precambrian
Paleozoic Era—Life Explodes
• 570-245 million years ago
• Hard parts appeared on organisms
• Early Paleozoic History
– Mountain building affected eastern North
America—long since eroded
Paleozoic Era—Life Explodes
• Early Paleozoic Life: “Age of Invertebrates”
• Restricted to seas
– Cambrian
• Trilobites
– Mud-burrowing scavengers
– More than 600 genera
– Ordovician—shallow seas
• Organisms with hard parts
• Brachiopods
– Adults attached to the sea floor, larvae free-swimming
• Cephalopods
– Mobile, highly developed mollusks; predators
Paleozoic Era—Life Explodes
• Late Paleozoic History
– Devonian, Mississippian, Pennsylvanian, and
Permian periods
– Pangaea
• Extreme seasons that caused one of the most
dramatic biological declines in history
Paleozoic Era—Life Explodes
• Late Paleozoic Life
– Land plants developed
– Fishes continued to adapt
– Devonian period: “Age of Fishes”
– Lobe-finned fish evolved into amphibians
– Insects
– Extensive coal swamps develop
Paleozoic Extinction
• Climates changed because of the
formation of Pangaea
• 75% of amphibians disappeared
• Up to 95% of marine life disappeared
• 1 of 5 mass extinctions
• Cause is uncertain
Mesozoic Era—Age of the
Dinosaurs
• 245 to 66 million years ago
• Mesozoic History
– Much of world’s land above sea level
– Breakup of Pangaea
– Mountains of western North America begin
forming
Mesozoic Era—Age of the
Dinosaurs
• Mesozoic Life
– Survivors of the great Paleozoic extinction
– Gymnosperms became dominant
– Reptiles adapt to dry climate
– Reptiles have shell-covered eggs that can be
laid on the land
– One group of reptiles led to the birds
– Many reptile groups and other animal groups
became extinct at the close of the Mesozoic
Cenozoic Era—Age of Mammals
• 66 million years ago to present
• North America
– Most was above sea level
– Mountain building, volcanism, and
earthquakes in the West
– In the East: stable with abundant marine
sedimentation; eroded Appalachians were
raised by isostatic adjustments
Cenozoic Era—Age of Mammals
– Western North America
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Rivers erode and form gorges (Grand Canyon)
Volcanic activity common
Coast ranges form
Sierra Nevada become fault-block mountains
Cenozoic Era—Age of Mammals
• Cenozoic life
– Mammals replace reptiles as dominant land
animals
– Angiosperms dominate the plant world
– Mammals evolve after the reptilian extinctions
of the Mesozoic
• Marsupials
• Placentals
Cenozoic Era—Age of Mammals
– Mammals diversify rapidly and some groups
become very large
• Hornless rhinoceros—nearly 16 feet high
• Many large animals became extinct
• Humans evolve