Earth Astronomy 311 Professor Lee Carkner Lecture 12

The high temperature of Venus is due to the lack of what compound? Carbon Dioxide Water Ammonia Sulfur Dioxide Oxygen

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

Terra -- The Earth Goddess Greeks and Romans personified the Earth as a mother goddess We use the old English names for the Earth, Sun and Moon, rather than the Latin ones

Earth Facts Size: 12700 km diameter Orbit: 1 AU (1.5 X 108 km) Description: wet, temperate, inhabited

Earth’s Atmosphere Composition: Very different from other atmospheres Outer planets: mostly H2

Early Atmosphere Where did the original atmosphere come from? Bombardment of icy planetesimals (comets) Early composition: Water (H2O) Ammonia (NH3)

Formation of Atmosphere Ultraviolet light breaks up some molecules (four key elements: C,H,O,N) CO2 dissolves in H2O, H2O rains out to form oceans, N2 left behind Life (plants) forms and produces O2 Final atmosphere -- O2 and N2

Earth’s Atmosphere

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 -- where water is lost by UV dissociation Outer Edge -- For our solar system habitable zone width is about 0.95-1.37 AU

Hypothetical Habitable Zone Too cold, try to warm up with more CO2 but CO2 forms clouds and blocks sunlight Too hot, water is destroyed can’t remove CO2 Just right, temperature kept stable at ~273 K (water is liquid) Hypothetical Habitable Zone

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

Planet Temperature Planets with no atmosphere have a temperature determined by radiation balance: Emit radiation back into space Temperatures are in Kelvin (K) A temperature scale where 0 K is absolute zero A summer day is about 300 K To convert K to F: TF = 1.8TK - 460

Radiative Power Hot objects absorb and emit energy based on the Stefan-Boltzmann law P = sAT4 Where: s is a constant = 5.67 X 10-8 (W/(m2 K4)) for a sphere A = 4pr2 T is the temperature of the object (in K)

Energy Balance If we compare the energy the Earth emits with the energy it gets from the Sun, we can find its temperature TE = [RS/(2 DS)]½ TS Where: TE TS is the temperature of the Sun RS DS is the distance from the Earth to the Sun

The Earth’s Surface What shapes the Earth’s surface? Water erosion 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 The two top layers of the Earth are the crust and the mantle 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

Plate Collision -- The Himalayas

The Grand Canyon

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: pressure or compression wave example: 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 There is a shadow zone where no P or S waves are detected Very faint P waves detected in shadow zone Refracted by solid inner core

Structure of the Earth

Structure of the Earth Crust: Mantle Outer core Inner core surface to 35 km Mantle 35-2900 km composed of silicates and heavier material Outer core 2900-5100 km Inner core 5100-6400 km composed of solid iron

Next Time Read Chapter 8 Just the moon parts

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