Download - Chapter 25 (Class)
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The History of Life on Earth
AP Chapter 25
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Figure 26.0 A painting of early Earth showing volcanic activity and photosynthetic prokaryotes in dense mats
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Overview: Lost Worlds
• Past organisms were very different from those now alive
• The fossil record shows macroevolutionary changes over large time scales including– The emergence of terrestrial vertebrates – The origin of photosynthesis– Long-term impacts of mass extinctions
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Fig. 25-1
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Fig 25-UN1
Cryolophosaurus
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The Age of the Earth
4.6 billion years
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Figure 26.2 Clock analogy for some key events in evolutionary history
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3.9 billion years ago
• Earth cooled, oceans formed, atmosphere contained nitrogen, CO2, methane CH4, ammonia NH3, and water vapor
• 1920’s Oparin and Haldane hypothesized that under those conditions, organic molecules could be formed
• 1953 Miller and Urey performed an experiment and produced organic molecules
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Other ideas
• Submerged volcanoes, deep-sea vents • Carbonaeceous chondrites found in
meteorites contain C compounds• Amino acid polymers from dripping organic
monomers onto hot sand or clay
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All of these point to the possibility of an abiotic
synthesis of life.
• Life requires:
accurate replication and metabolism• Protobionts – collections of abiotically
produced organic molecules surrounded by a membrane
• Liposomes – evidence of this possibililty
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Fig. 25-3
(a) Simple reproduction by liposomes (b) Simple metabolism
Phosphate
Maltose
Phosphatase
Maltose
Amylase
Starch
Glucose-phosphate
Glucose-phosphate
20 µm
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First replicating molecule…
• RNA• Why – capable of copying itself
using ribozymes – enzyme-like RNA catalysts
• DNA would have replaced RNA as a better storage molecule
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Figure 26.11 Abiotic replication of RNA
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How is the age of fossils and rocks determined?
• Radiometric dating – using half-lives of radioactive isotopes
• Carbon-14 5,730 years• Also patterns of magnetic reversal of
the earth is used
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3.5 billion yearsFirst Single-Celled Organism
• Oldest known fossils are stromatolites, rocklike layers of prokaryotes and sediment.
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Figure 26.3 Early (left) and modern (right) prokaryotes
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2.7 billion years agoOxygen
Evidence of oxygen accumulation from cyanobacteria in banded iron formations
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2.1 billion years agoeukaryotic cells
• Fossils of eukaryotic cells• Mitochondria and chloroplasts may have
originated as prokaryotes engulfed by other prokaryotes in endosymbiosis.
• In serial endosymbiosis, mitochondria probably evolved first
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1.5 billion years agoMulticellular organisms
• Oldest known fossils are algae• Severe ice ages (Snowball Earth)
prevented diversity of eukaryotes for awhile
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535 – 525 Cambrian Explosion
• Great diversity of all types of eukaryotes
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500 myaMovement onto Land
• Evolved adaptations to live on land and prevent dehydration
• Plants and fungi colonized land together
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250 myaFormation of Pangaea
• Destroyed and altered habitats, changed climates, created geographic isolation
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Mass Extinctions
• There have at least 5 mass extinctions.• Permian – 250 mya, over 90% of marine and
terrestrial species disappeared; maybe due to volcanoes, Pangeae, glaciation
• Cretaceous – 65 mya; ½ marine and many terrestrial forms, including dinosaurs; due to environmental changes or asteroids hitting the earth
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• Mass extinctions provide many habitats and available niches to organisms that survive which leads to adaptive radiation.
• For ex, mammals did not change much until the after 65 mya and the extinction of the dinosaurs.
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Evolution is not goal-oriented!
• Often very complex organs have evolved gradually from simpler structures, such as eyes.
• Evolutionary novelties may arise by modification of existing structures.