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The Archean Eon 3.8 BYA to 2.5 BYA Oceans and Life

The Archean Eon 3.8 BYA to 2.5 BYA Oceans and Life. Crust Hardens; Global Ocean Forms. Planet has cooled enough that surface temperature allows condensation Atmosphere is full of an ocean of water vapor 100,000 yrs of rain….

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The Archean Eon 3.8 BYA to 2.5 BYA Oceans and Life

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  1. The Archean Eon3.8 BYA to 2.5 BYAOceans and Life

  2. Crust Hardens; Global Ocean Forms • Planet has cooled enough that surface temperature allows condensation • Atmosphere is full of an ocean of water vapor • 100,000 yrs of rain…. • No land above water; crust is below water, in what are now ocean basins • Hot/warm water, high energy, soup of chemicals

  3. How Do We Know About Crust? • The oldest rocks date back 4.1 billion years • Zircon crystals in volcanic ash layers • The Precambrian shield has had very little faulting, folding for my’s (stable cores of all continents, often covered by layers of younger sediments) • Ancient rocks found on almost every continent

  4. Surface is Deadly to LifeNo Ozone Layer • UV radiation at surface (no ozone/O3) layer • No oxygen in atmosphere • Meteor bombardment has slowed, but still occurs

  5. What is Earth Like? • Atmosphere – where do gases come from? • Oceans • Geosphere? • Biosphere? • What does life need? • What is life? • Where could it arise? (image: cyanobacteria)

  6. Possible Locations • Below surface of ocean • Rocky/geosphere – inside grains of rock? • “clouds” – vapor and elements • Volcanoes; deep sea vents (black or white smokers, geysers, • Boundary between rocky and watery layer? • Elsewhere in solar system first and then “carried” to earth (hitching a ride?)

  7. Evidence of Life: What to Look For? • Chemical footprints • Isotopes of carbon • What kind of material can survive extreme heat? Zircons, “shields,” greenstones… • West Antarctica, Greenland, W. Australia • Organic rich meteorites – organic molecules for first life from space?

  8. Origin of Living Things: Procaryotic Cell • “Before kernel” . Cells with no nuclei. DNA/RNA proteins encased in a cell wall that can reproduce; • Millions of new cells in minutes; one out of a million mutates • New adaptation capabilities, withstand environmental challenge • Archaen first – most ancient; extremophiles? • Then Bacteria

  9. Procaryotes Rule Earth • 40 ya modern discovery! Life (and microbes) in extreme places • New domain of life called Archaen (added to bacteria, eucaryotic) • Archaea include bacteria, extremophiles, protists

  10. Photosynthesis evolves • First life on Earth – not photosynthetic • Extremophiles; lovers of harsh conditions • Bacteria - anaerobic • Chemical evolution of the cell (through eons of mutations) leads to photosynthesis • Photosynthetic organisms procaryotic bacteria) take over • Chemistry of earth begins to change

  11. Stromatolite-Building Communities • rock-like buildups of microbial mats that form in limestone • include oldest known fossils, 3.5 bya • encode role ancient microorganisms played in evolution of life and shaping earth's environments. • Extensive fossil record of stromatolites; spans 4 by of geological history; occupied every conceivable environment that ever existed. • Today, nearly extinct in marine environments, living a precarious existence in only a few places worldwide. • Modern stromatolites discovered in Shark Bay, Australia in 1956

  12. Stromatolites – Oxygen Excreting “Colonies” Populated Earth

  13. Iron Formations • Geological Record marks rise in oxygen; iron moves freely if no oxygen • Free oxygen causes rocks and oceans to rust • Builds up in rocks • Then builds up in atmosphere • 2.5 BYA Oxygen Revolution

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