Transcript 17-2 Earth`s Early History

17-2 Earth's Early History
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Earth is the only known planet
known to support life!
Conditions Necessary for Life:
1. Liquid water
2. A moderate temperature
3. Free oxygen in atmosphere
4. Sunlight
5. Absence of toxic substances in
atmosphere
6. Absence of lethal radiation
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17-2 Earth's Early History
Formation of Earth
Formation of Earth
• Earth is made mostly of rock!
• High temps on Earth caused most rock to
melt and separate.
• Dense materials (iron and nickel) sank and
formed the core.
• Lighter materials settled above the core
forming the mantle and crust.
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17-2 Earth's Early History
The active volcanoes on Earth released
water vapor which built up in the
atmosphere.
The water vapor condensed and fell
back to Earth as rain.
Over millions of years, the liquid water
collected in depressions on Earth’s
rocky surface and formed oceans.
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17-2 Earth's Early History
Formation of Earth
In addition to water vapor, the
erupting volcanoes released other
gases forming Earth’s early
atmosphere (gases that surround
Earth).
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17-2 Earth's Early History
Formation of Earth
These gases were methane,
hydrogen, nitrogen,
ammonia, carbon dioxide,
and carbon monoxide.
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17-2 Earth's Early History
Today’s atmosphere contains free oxygen
(oxygen gas that is not combined with
other elements) and a layer of ozone that
protects living things from harmful
radiation.
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17-2 Earth's Early History
The First Organic Molecules
The Beginning of Life on Earth
The lack of free oxygen in Earth’s early atmosphere
would have prevented the survival of most modern
organisms so…..
In the 1950s, Stanley Miller and Harold Urey tried
to model early Earth Conditions.
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17-2 Earth's Early History
The First Organic Molecules
Miller and Urey's experiments suggested
how mixtures of organic compounds
needed for life could have formed from
simpler compounds present on an early
Earth.
Their experiment showed that amino
acids could form from matter present on
early Earth.
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17-2 Earth's Early History
The First Organic Molecules
Miller and Urey’s Experiment
Mixture of gases
simulating
atmosphere of
early Earth
Spark simulating
lightning storms
Condensation
chamber
Water
vapor
Cold water cools
chamber, causing
droplets to form.
Liquid containing amino
acids and other organic
compounds
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17-2 Earth's Early History
Free Oxygen
Primitive Organisms and the
Endosymbiotic Theory
• Fossil evidence indicates that the first
organisms appeared in Earth’s oceans about
3.5 billion years ago
• These organisms formed without Oxygen
• They were prokaryotes!
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17-2 Earth's Early History
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17-2 Earth's Early History
Fossils showed that cyanobacteria
(prokaryotes that make food by
photosynthesis) became common
in shallow areas of Earth’s oceans
about 3 billion years ago.
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17-2 Earth's Early History
Photosynthesis by cyanobacteria gradually
increased the amount of oxygen in the
atmosphere creating free oxygen.
This free oxygen bred life to more complex,
oxygen breathing life forms!
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17-2 Earth's Early History
Origin of Eukaryotic Cells
What hypothesis explains the origin of
eukaryotic cells?
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17-2 Earth's Early History
Origin of Eukaryotic Cells
The Endosymbiotic Theory
The endosymbiotic theory proposes that
eukaryotic cells arose from living
communities formed by prokaryotic
organisms.
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17-2 Earth's Early History
Origin of Eukaryotic Cells
Endosymbiotic Theory
Ancient Prokaryotes
Chloroplast
Aerobic
bacteria
Nuclear
envelope
evolving
Ancient Anaerobic
Prokaryote
Photosynthetic
bacteria
Plants and
plantlike
protists
Mitochondrion
Primitive Aerobic
Eukaryote
Primitive Photosynthetic
Eukaryote
Animals,
fungi, and
non-plantlike
protists
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17-2 Earth's Early History
Early Eukaryotes
• The first eukaryotes evolved around 2 billion years ago.
• Included algae.
• Photosynthesis by algae added more oxygen to the
atmosphere.
• Sexual reproduction evolved around 1.2 billion years ago
• Life became much more varied and complex about 540
million years ago.
• This event is known as the Cambrian Explosion!
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17-2 Earth's Early History
• All the major animal groups first
appeared during the Cambrian
Period.
• Fossil evidence shows plant life
started around 480 million years
ago.
• Land plants are the major source of
atmospheric oxygen today.
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17-2 Earth's Early History
Order of life on Earth
Anaerobic Prokaryotes
Photosynthetic Prokaryotes
Unicellular Eukaryotes
Multicellular Eukaryotes
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