Habitability of Earth and Long-term Climate Change

Habitability of Earthand Long-term Climate Change ASTR 1420 Lecture #7 Sections 4.4 & 4.5

Formation of Stars and Planets Animation on the formation of star+planets. Just to understand following slide a little better. Detailed information on the planetary system formation will be handled in later lectures.

Formation & evolution of Earth Today’s Lecture in a single slide!!

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 1200km 2000km 3000km

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 (i.e., formation heat) • Potential energy of sinking heavy material • Radioactive decay energy All terrestrial worlds in out solar system had similar melting and differentiating…

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

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

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. Seven major plates

At plate boundaries… Separating boundary Colliding boundary Sliding boundary

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

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

So, plate-tectonics is cool. What does it have to do with astrobiology?  Importance of plate-tectonics will be addressed in terms of “long-term climate stability” in later slides…

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

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

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

Aurora Borealis : Aurora Australis : Auroras : northern & southern lights

Aurora in Georgia! Oct. 29, 2003. Dahlonega, GA Triggered by a coronal mass ejection (CME)… What’s CME? Google for it.

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

Greenhouse gases (H2O, CO2, CH4): effectively “trap” infrared light Without the greenhouse effect, global average temperature of the Earth would be 30°F! Greenhouse effect

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

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!

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?

Serbian scientist: Precession Obliquity Eccentricity Milankovitch cycles http://www.youtube.com/watch?v=wLAYRdSnRSI

Snowball Earth Ice reflects light 90% while water does so only 5% Long deep ice ages : 750-580 Myr ago, 2.4-2.2 Gyr ago glaciers all the way to equator!  putting stresses on life (causing faster evolution)  Cambrian explosion!!

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?

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 Earth • Chapter/sections covered in this lecture : 4.4 & 4.5

Habitability of Earth and Long-term Climate Change