Earth Astronomy 311 Professor Lee Carkner Lecture 12

Terra -- The Earth Goddess 

Earth Facts  Size: km diameter   Orbit:  Description:

Earth’s Celestial Motions  Earth is tilted on its axis by 23 1/2 degrees   Earth has large satellite, The Moon    May stabilize tilt of axis

Earth’s Atmosphere  Composition:     Very different from other atmospheres  

Early Atmosphere  Where did the original atmosphere come from?    Early composition:    

Formation of Atmosphere  Start with CO 2, H 2 O, CH 4, NH 3   C, H, O form H 2 O, CO 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   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    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?  It has the right temperature for liquid water (~273 K) because:   Not too close or too far from the Sun 

Climate   Two basic sources of convection    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?    Also, volcanoes and cratering  Resurfacing is cyclical and constant   Unlike other planets the Earth does not have many craters 

Plate Tectonics  The two top layers of the Earth are the crust and the mantle    Crust is broken up into plates that float on the upper mantle  Plates move around and crash into each other forming trenches and mountains 

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

Water on the Earth

Plate Collision -- The Himalayas

The Grand Canyon

Meteor Crater

The Earth’s Interior  The crust and atmosphere are very thin compared the rest of the planet (like the skin of an orange)   We learn about them by studying the seismic waves from earthquakes

Seismic Waves  Types of waves:  P waves:   S 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    There is a shadow zone where no P or S waves are detected   Very faint P waves detected in shadow zone 

Structure of the Earth

 Crust:    Mantle    Outer core    Inner core    Density increases toward the center

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