Earth Astronomy 311 Professor Lee Carkner Lecture 12.

Earth

Astronomy 311Professor Lee

CarknerLecture 12

The high temperature of Venus is due to the lack of what compound?

a) Carbon Dioxideb) Waterc) Ammoniad) Sulfur Dioxidee) Oxygen

Which of the following is not evidence for volcanism on Venus?

a) Shield volcanoesb) Lava domesc) A smoothed surfaced) Smoke rising from active

volcanoese) 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, CO2 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 (H2O) Ammonia (NH3)

Formation of Atmosphere

Start with CO2, H2O, CH4, NH3

C, H, O form H2O, CO2

Life (plants) forms and produces O2

Final atmosphere -- O2 and N2

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: TF = 1.8TK - 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 0.95-1.37 AU

Hypothetical Habitable Zone

Too hot,water is destroyedcan’t remove CO2

Too cold,try to warm upwith more CO2

but CO2 formsclouds and blocks sunlight

Just right,temperaturekept stableat ~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

Structure of the Earth

Crust: surface to 35 km

Mantle 35-2900 km composed of

silicates and heavier material

Outer core 2900-5100 km

Inner core 5100-6400 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