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Habitability of Earth

Habitability of Earth. ASTR 1420 Lecture #7 Sections 4.4 & 4.5. Formation of Stars and Planets. Formation & evolution of Earth. Earth’s long-term stability depends on volcanism, plate tectonics  we need to know the internal structure! How do we know? Overall density versus surface rock

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Habitability of Earth

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  1. Habitability of Earth ASTR 1420 Lecture #7 Sections 4.4 & 4.5

  2. Formation of Stars and Planets

  3. Formation & evolution of Earth

  4. Earth’s long-term stability depends on volcanism, plate tectonics  we need to know the internal structure! How do we know? Overall density versus surface rock Gravity probe? Magnetic field? But, mostly from seismic waves! Interior structure Core : Nickel and Iron. Inner core (solid), outer core (liquid!) Mantle : rocky material (silicate minerals) Crust : lowest-density rock. Interior Structureof the Earth • Lithosphere : a layer of cold, rigid rocks above warmer, softer rocks.

  5. Materials that are separated according to their densities… Differentiation • By the time of the Moon creating impact, Earth was already differentiated! • How did it happen so fast? • Earth was molten (or at least nearly molten) throughout its interior… • Heat sources of the melting • Impact heat • Potential energy of sinking heavy material • Radioactive decay energy All terrestrial worlds in out solar system had similar melting and differentiating…

  6. Continental Drift was proposed by meteorologist and geologist Alfred Wegener in 1912 The idea was inspired by the puzzle-like fit of South America and Africa, indicating these two continents were part of a single “supercontinent” about 200 million years ago Continental Drift

  7. Plate Tectonics : Wilson Cycle http://www.youtube.com/watch?v=ZLJLFYXp-0Q

  8. Plate Tectonics • Internal heat makes hot material expand and rise while cooler material on top contracts and falls • Plate tectonics produces and recycles seafloor crust (that is why the seafloor crust is usually less than 200 million years old). At ocean trenches, the seafloor crust pushes under the less dense continental crust, returning the seafloor crust to the mantle and may cause volcanic eruptions.

  9. At plate boundaries…

  10. Sometimes, localized plume of mantle material get uplifted… Hawaiian islands Yellow Stone Park Hot Spots

  11. On-going… • In ~100 Myrs, California will slide northward to Alaska, the Mediterranean Sea will become mountains, Australia will merge with Antarctica

  12. Charged particles from solar flares interact with earth’s magnetic field and atoms and molecules in Earth’s atmosphere and produce aurora Magnetic Field

  13. Cause of Magnetic Field • Requirements for a magnetic field • Electrically conducting fluid • Convection • Rotation of the planet Electromagnet

  14. Magnetic field as a shield! High velocity electrified gas (plasma) blows into the Earth at speed of ~250 miles/second! http://www.gsfc.nasa.gov/gsfc/spacesci/pictures/20020509imagessu/magneticfield_mpeg.mpg

  15. Aurora Borealis : Aurora Australis : Auroras : northern & southern lights Aurora seen at UL : Washington UR : Canada LL : Texas

  16. Aurora in Georgia! Oct. 29, 2003. Dahlonega, GA Triggered by a coronal mass ejection…

  17. Other Planets, too! Jupiter seen in X-ray (Chandra satellite)

  18. Greenhouse gases (H2O, CO2, CH4): effectively “trap” infrared light Without the greenhouse effect, global average temperature of the Earth would be 30°F versus current value of 59°F! for a very similar size and distance from the Sun compared to those of Earth, Venus’ global average temperature is 878°F! Why?? Greenhouse effect

  19. On Earth, CO2 content in the air is regulated by the Carbon Dioxide Cycle (the carbonatesilicate cycle, or the inorganic carbon cycle) to avoid runaway Greenhouse effect Carbonate rocks : limestone, calcite, dolomite, chalk, … CO2 Cycle CO2 in the Earth : atmosphere 1, ocean 60, rocks 170,000

  20. The cycle is about 400,000 years The CO2 cycle acts as a thermostat For the warm Earth, carbonate minerals forms in the oceans at a more rapid rate, and takes away more CO2 Regulation of Earth’s Climate What global warming? We don’t need to worry about it since the CO2 cycle will take care of it!! Really??  runaway greenhouse effect!

  21. Plate tectonics!! Ice Ages • Different configuration of continents can cause a climate change (hundreds of million years cycle). • But, cycles of ice ages are much faster! • Why?

  22. Serbian scientist: Precession Obliquity Eccentricity Milankovitchcycles Earth's most common mechanism for climate change http://www.youtube.com/watch?v=wLAYRdSnRSI

  23. Snowball Earth

  24. Earth’s long-term Habitability • Several Key Factors • Volcanic outgassing atmosphere • Magnetic field shield  atmosphere • Moderate greenhouse effect • CO2 cycle as a climate regulator • Milankovitch cycles and ice ages • Some extreme cases (snowball Earth and hothouse) ? Should we expect to find plate tectonics and CO2 cycle on other planets?

  25. In summary… Important Concepts Important Terms Core, mantle, crust (+ lithosphere) Plate tectonics Milankovitch cycles Differentiation Precession, obliquity, eccentricity • Plate Tectonics • CO2 cycle and climate regulation • Greenhouse effect • Runaway greenhouse effect • Snowball/Hothouse Earth • Chapter/sections covered in this lecture : 4.4 & 4.5 • Threats to Life : next class!

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