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The Hadean & Archean

The Hadean & Archean

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The Hadean & Archean

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Presentation Transcript

  1. The Hadean & Archean “It’s the Earth Jim, but not as we know it.”

  2. Hadean & Archean: 2500-4600 Myrs

  3. Archean Divided into:

  4. Hadean/Archean “Evidence” • Problems • Very few rocks/minerals exist from this period • Most have been metamorphosed, or buried • No fossils exist in Hadean, Minimal in Archean • Rely on: • Few rocks that we have • Moon, Meteorites& other planets • Models 4.4 Gyr Zircon Crystal

  5. Rocks Older than 2.5 Gyrs

  6. The Neighborhood: “Dim” Sun

  7. The Neighborhood: “Near” Moon = Shorter Day About 10 hrs

  8. Origin of the Moon: 4.5 Gyrs

  9. Lunar Evidence • Moon does not orbit around the earth’s equator • The moon is retreating from the Earth (but could never have been closer than 24,000 km) • Moon is depleted in iron and “iron-loving” elements (it has a low density) • Moon is dry (no water in the minerals) • Oxygen isotope ratio in moon rocks is the same as the Earth • Lunar highlands have been dates at about 4.5 Byrs

  10. Lunar Hypothesis • Capture: Formed somewhere else and was captured • Twin Planet: Formed from material left over from the Earth • Fission: “Budded” off the Earth Problem: It has the same Oxygen Chemistry as the Earth indicating it formed in the same part of the Solar System

  11. Lunar Hypothesis • Capture: Formed somewhere else and was captured • Twin Planet: Formed from material left over from the Earth • Fission: “Budded” off the Earth Problem: Moon has much less iron than the Earth and is no volatiles (water & gases)

  12. Lunar Hypothesis Problem: Earth was not spinning fast enough for this to be realistic. • Capture: Formed somewhere else and was captured • Twin Planet: Formed from material left over from the Earth • Fission: “Budded”off the Earth

  13. Lunar Hypothesis • Capture: Formed somewhere else and was captured • Twin Planet: Formed from material left over from the Earth • Fission: “Budded” off the Earth • Collision: Formed when a Mars-sized body collided with the Earth Explains (1) isotopes, (2) lack of iron and volatiles, and (3) consistent with Earth’s spin rate.

  14. Animation Link

  15. Lunar Evidence / Impact  • Moon does not orbit around the earth’s equator • The moon is retreating from the Earth (but could never have been closer than 24,000 km) • Moon is depleted in iron and “iron-loving” elements (it has a low density) • Moon is dry (no water in the minerals) • Oxygen isotope ratio in moon rocks is the same as the Earth • Lunar highlands have been dates at about 4.5 Byrs     

  16. Hadean Earth 2004 - Fred Sulahria

  17. Hadean: What We Do Know… Earth was a very different place! • Major features of the Earth developed: • atmosphere (throughout Hadean) • oceans (water by 4.4 Gyr, stable oceans by 3.8 Gyr) • crust and continents (by 4.4-4.0 Gyr) • plate tectonics starts (about 4.0 Gyr) • magnetic field (about 4.5 Gyr) • life? (no evidence yet…)

  18. Early Earth Driven by Heat From: Accretion Differentiation Radioactive Decay

  19. Heat Escapes by: • Convection • Conduction • Radiation Resulting in Convection of Interior and Volcanism

  20. Hadean Surface Dominated By: • Meteorite Bombardment • Volcanism

  21. Heavy Bombardment Period

  22. Heavy Bombardment on the Moon

  23. Bombardment may have led to a Temporary “Magma Ocean”

  24. Komatiites Magma Solidified into Early Crust Ultramafic, Dense, Uniform

  25. Atmosphere

  26. Atmospheric Formation • Hypothesis: Captured from Solar Nebula • Mostly Hydrogen and Helium • Would have been quickly lost If initially lost - where did the present atmosphere come from? Accreted as hydrous minerals and outgassed from volcanoes Returned to Earth from comets

  27. Secondary Atmosphere - Outgassing • Initially Composed of: • Ammonia (NH3) • Hydrogen (H2) • Carbon dioxide (CO2) • Methane (CH4) • Water vapor (H2O) • Nitrogen (N2)

  28. Similar to Saturn’s moon: Titan

  29. One Reconstruction(Others have much more Carbon Dioxide in Hadean)

  30. Note: No Significant Oxygen! • Evidence: • No Rust Minerals • Pyrite and Uraninite Conglomerates(normally oxidize) • Extensive carbon-rich rocks Witwatersrand conglomerate, South Africa (Middle Archean)

  31. Atmospheric Evolution Primary - Captured from Solar Nebula - Mostly Hydrogen and Helium - Quickly Lost Secondary - Formed by Outgassing by Volcanoes Tertiary - Modified by Life (addition of Oxygen)

  32. Oceans

  33. “Raining” of the Oceans

  34. “Vaporization” of the Oceans

  35. Hadean Oceans • Characteristics • Liquid Water existed at 4.4 Gyrs • “Ephemeral” (periodically vaporized) • Acidic (water + carbon dioxide = carbonic acid) • Probably “salty” • Stabilized by end of Hadean (about 3.8 Gyrs) • Evidence • Jack Hills Formation zircon crystals with water inclusions • solar system evidence for heavy bombardment and models • no limestones, atmospheric models • acidic water (dissolves ions) • first limestones & sedimentary rocks

  36. One Reconstruction(Other hypothesize much less water from comets)

  37. Return to the Crust

  38. Continents FormationRequires Plate Tectonics

  39. Intermission:See Plate Tectonics ppt

  40. Set the “Wayback Machine” to return to the Hadean…

  41. Heat Generated by Radioactive Decay Hadean Earth was much hotter! Convection was more intense

  42. Rapid Convection Created “Mini” Plates that were Quickly Subducted & Destroyed

  43. Subduction Createsmore Felsic Volcanic Islands

  44. As Plates Move - Islands “Accrete” to Form Larger Islands

  45. Greenstones & Tonalites (Granites)

  46. Continental Crust Forms 3.96 Billion Year Old Gneiss

  47. Archean Crust Oldest Rocks Oldest Minerals

  48. Continental Evolution:One Reconstruction Up to 60% by the Proterozoic

  49. Hadean Summary