the origins of life the big bang occurred about 18 billion years ago, creating the universe. the...
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The Origins of Life
• The Big Bang occurred about 18 billion years ago, creating the universe.
• The Earth formed about 4.6 billion years ago.
• Life on Earth probably originated between 3.5 and 4 billion years ago.
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Evidence of First lifeStromatolites
• Stromatolites are mounds of banded sediment formed by mobile cyanobacteria.
• They are found in the warm waters of Australia and off the coast of Baja, Mexico.
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Evidence of First LifeStromatolites
• Stromatolites have been found that date back to 3.5 billion years ago.
• They are strikingly similar to those produced by modern day bacteria.
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Evidence of First LifeFossils
• Fossilized filamentous bacteria has also been found that dates back to 3.4 billion years.
• This fossilized prokaryote was found in a 3.4 billion year old stromatolite in Western Australia.
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Early Earth
• When the Earth first formed, it was very different from its current state.
• It was filled with reducing gases, like H2, NH3, CH4, CO, and CO2.
• Most notably, the atmosphere of early Earth was completely anaerobic.
• It lacked a protective ozone layer.
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Chemical Origins
• In the 1920’s, Oparin and Haldane predicted that the conditions of early Earth favored the spontaneous formation of organic compounds.
• In 1953, Miller and Urey tested this hypothesis.
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From Molecules to Cells
1. Small organic monomers formed in reducing atmosphere.
2. Monomers joined to form polymers – binding sites in clay helped concentrate the monomers, while metal ions acted as catalysts.
3. Polymers aggregated to form protobionts.4. A molecule of heredity originated.
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Protobionts
• Protobionts are aggregates of molecules that have some cell-like qualities such as:– Self-assembly– Response to osmotic
forces– Ability to store a
membrane potential– Engulfing and splitting
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First Life
• Prokaryotic• RNA as genetic material• Heterotrophic – absorbed organic molecules from
surroundings• Anaerobic – oxygen was not present in
atmosphere until it was put there by photosynthetic bacteria as a waste product (began accumulating about 2 billion years ago
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Origin of photosynthesis
• Some time after the first living things appeared, cells developed that could perform photosynthesis.
• These organisms put oxygen into the air as a waste product.
• About 1.5 billion years ago, oxygen still only made up about 1% of the atmosphere
• Accumulation of oxygen in the atmosphere is thought to have ended chemical evolution
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Open for debate
• Some scientists believe organic molecules came to Earth from outer space. Meteors have been found containing amino acids and nucleic acids (including several amino acids nonexistent on Earth).
• There may have been a simpler hereditary molecule that preceded RNA, or maybe RNA was never genetic material.
• Maybe life began near hydrothermal vents (and still forms there?)
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Taxonomy – the classification of living things
• From that first cell, life has diversified into millions of different forms.
• These forms are divided into five major kingdoms: Animalia, Plantae, Fungi, Protista, and Monera.