Earth Astronomy 311 Professor Lee Carkner Lecture 12

The high temperature of Venus is due to the lack of what compound? a)Carbon Dioxide b)Water c)Ammonia d)Sulfur Dioxide e)Oxygen

Which of the following is not evidence for volcanism on Venus? a)Shield volcanoes b)Lava domes c)A smoothed surface d)Smoke rising from active volcanoes e)Sulfur in atmosphere

Terra -- The Earth Goddess   We use the old English names for the Earth, Sun and Moon, rather than the Latin ones

Earth Facts  Size:  largest terrestrial planet  Orbit:  Description: wet, temperate, inhabited

Earth’s Atmosphere  Composition:    small amounts of water vapor, CO 2 other gasses  Very different from other atmospheres  Inner planets:  Outer planets:

Early Atmosphere  Where did the original atmosphere come from?   Bombardment of icy planetesimals (comets)  Early composition:   Water (H 2 O)   Ammonia (NH 3 )

Formation of Atmosphere  Start with CO 2, H 2 O, CH 4, NH 3   C, H, O form H 2 O, CO 2   Life (plants) forms and produces O 2  Final atmosphere -- O 2 and N 2

Earth’s Atmosphere

Atmosphere and Temperature  Planets with no atmosphere have a temperature determined by radiation balance:    For a steady temperature, both rates must be equal   K stands for Kelvin, a temperature scale where 0 K is absolute zero  The coldest anything can get  To convert K to F:  T F = 1.8T K - 460

The Habitable Zone  In order to support life a planet must be in the habitable zone   Width of zone determined by the effectiveness of the carbonate-silicate cycle  Inner Edge --  Outer Edge --  For our solar system habitable zone width is about AU

Hypothetical Habitable Zone Too hot, water is destroyed can’t remove CO 2 Too cold, try to warm up with more CO 2 but CO 2 forms clouds and blocks sunlight Just right, temperature kept stable at ~273 K (water is liquid)

Why is the Earth Habitable?   Large enough to hold an atmosphere   Has both water and plate tectonics for carbonate-silicate cycle

Climate   Two basic sources of convection  Bottom of atmosphere is warmer than top   The Earth’s rotation breaks the atmosphere up into convection cells that keep the air circulating, producing global weather patterns

The Earth’s Surface  What shapes the Earth’s surface?    Resurfacing is cyclical and constant  Plate tectonics raise up mountains, water erodes them down, the silt collects on the ocean floor and forms the rock to make the next mountains   Craters on Earth are largely obliterated by erosion

Plate Tectonics   Upper mantle is soft and plastic  Crust is hard and rigid   Plates move around and crash into each other forming trenches and mountains  Plates move a few inches a year

How Plate Tectonics Work

Plate Boundaries

Water  The Earth has more liquid water on its surface than any other planet   Water is present on Earth in all three phases (ice, liquid water, vapor) and continuously cycles between them

The Earth’s Interior   We cannot view the inner layers directly (can’t drill deep enough)  We learn about them by studying the seismic waves from earthquakes

Seismic Waves  Types of waves:  P waves: pressure or compression wave   S waves: shear waves   The different densities of the inner earth refract the waves   When an earthquake occurs we can measure the strength of S and P waves all over the Earth

Earthquake Studies of the Earth’s Interior

Seismic Waves and the Earth’s Interior  No S waves detected on opposite side of Earth   Core must be liquid   Core mantle boundary refracts wave out of this zone   Refracted by solid inner core

Structure of the Earth

 Crust:  surface to 35 km   Mantle  km  composed of silicates and heavier material  Outer core  km   Inner core  km  

Next Time  Read Chapter 8  Just the moon parts  Observing Thursday 8-9 pm

Summary  Earth is unique for at least two reasons  Large amounts of liquid water  constantly reshapes the surface  Large amounts of free oxygen  produced by life  Earth has liquid water and life because it is in the habitable zone

Summary: Atmosphere  Earth’s initial atmosphere composed of CHON  H and O form water -- oceans  C and O form carbon dioxide -- rock  N stays in atmosphere  Plants produce oxygen  Mild temperature maintained by carbonate-silicate cycle

Summary: Surface  Solid iron inner core, liquid iron outer core, solid mantle and crust  Crust is broken up into plates which slide around on the upper mantle  Plate tectonics and erosion constantly alter surface