scientists have divided geologic history into 4 main parts: precambrian time paleozoic era mesozoic...
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ERAS OF THE GEOLOGIC TIME SCALE
SCIENTISTS HAVE DIVIDED THE EARTH’S HISTORY INTO 4 MAJOR PARTS:
THE GEOLOGIC TIME SCALE
Scientists have divided geologic history into 4 main parts:
Precambrian TimePaleozoic EraMesozoic EraCenozoic Era
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Precambrian Time
4.6 billion – 543 million years ago Life began during this time Atmosphere made of water vapor, CO2 & N2
Volcanic eruptions, meteorites, violent storms & intense solar radiation
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Origin of Life?
• Extraterrestrial• Life came from outside the planet(i.e. meteor)
• Creation• Divine forces created life
• Non-Living Matter• Spontaneous assembly of molecules
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4 billion years ago - Earth began to cool
Water condensed and fell as rain
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Atmosphere of early Earth Hydrogen (H2) Volcanic gas
(i.e. methane (CH4), ammonia (NH3), CO, SO2, N2, CO2)
No free oxygen or ozone
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Energy stimulated chemical reactions
=ProteinsNucleic AcidsLipidsCarbohydrates
UV
+
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How Did Life Begin?
In the oceans Energy from radiation
and storms caused simple chemicals in the oceans & atmosphere to react
More complex molecules were made Molecules joined to form cells Prokaryotes: single-celled organisms
(without a nucleus) that did not need O2 to survive
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Photosynthesis & Oxygen Cyanobacteria (type of prokaryotic
organism) appears over 3 bya Uses sunlight to produce food
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Photosynthesis & Oxygen Oxygen gas is released into oceans & air Oxygen molecules react to form Ozone,
which absorbs harmful radiation form the sun
Now possible for life to exist on Earth’s surface
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Photosynthesis & Oxygen
VOCs Volatile organic compounds
NOx Nitrogen-oxygen compounds
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Multicellular Organisms
Eukaryotes appear in the fossil record Organism that contain a nucleus Will evolve into organisms composed of many
cells
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Paleozoic Era (543 – 248 mya)
“Old life” or “Ancient life” Large fossil record
Sponges, coral, squid, clams, trilobites, fish, sharks
Reptiles, amphibians, fish, worms, & ferns first appear
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Paleozoic Era – Life on Land
Plants, fungi, & air-breathing animals slowly colonized land Crawling insects first animals to live on land Reptiles & winged insects appear near the end
of era LARGEST Mass extinction marks end of
era 90% of species extinct Oceans completely changed
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Mesozoic Era (248 – 65 mya)
“Middle Life” or “Age of Reptiles” Dinosaurs dominate Earth for 150 million
yrs First birds appear Conifers appear Flowering plants appear late in era
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End of Mesozoic Era
Mass Extinction Dinosaurs Many other plant & animal species Meteorite hit Earth
Dust, smoke, fires Temperatures dropped
for many years
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Cenozoic Era (65 mya – today)
“Recent Life” or “Age of Mammals” Many mammals, birds, insects &
flowering plants Saber-toothed cats,
camels, small horses
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Cenozoic Era Today
Era we are currently living in Climate changed many times during era
Periods of ice ages Animals migrate, adapt, or become extinct