The Earth as a Planet

Earth as a Planet

• Densest planet in the solar system

• Largest terrestrial planet • Only planet (currently) to have

– Plate tectonics – Liquid water on the surface ? – Life ? – Oxygen-rich atmosphere

PTYS/ASTR 206 Earth 3/4/08

PTYS/ASTR 206 Earth 3/4/08

The Earth’s Internal Structure

• The Earth’s inner and outer cores are composed of almost pure iron with some nickel mixed in

• The mantle is composed of iron-rich minerals

• Both temperature and pressure steadily increase with depth inside the Earth

Earthquake Distribution

PTYS/ASTR 206 Earth 3/4/08

Drift of Continental Plates over time• About a few centimeters per

year – Ranging from about the rate at

which fingernails grow, to that of hair growth !

• The continents were all together around 250 million years ago – The Earth is 4.56 Billion

years old – That is only 0.4% of the

lifetime of the Earth • In terms of a human

lifespan, that’s about 4 months !

Plate tectonics is responsible for most of the major features of the Earth’s surface, including mountain ranges, volcanoes, and the shapes of the continents and oceans

• Plate tectonics is involved in the formation of the three major categories of rocks: !

• igneous rocks – cooled from molten

material • sedimentary rocks

– formed by the action of wind, water, and ice

• metamorphic rocks – altered in the solid

state by extreme heat and pressure

PTYS/ASTR 206

• Earth’s atmosphere consists of mostly nitrogen (78%) and oxygen (21%). !

• It is divided into layers – Other planets have a similar

structure, although the details are different

!• In the troposphere,

temperature decreases with altitude !

• Ozone molecules in the stratosphere absorb ultraviolet light; thus temperature rises with altitude

The Structure of Earth’s Atmosphere

Evolution of Earth’s Atmosphere

• First Atmosphere – Mostly H2 and He !

• Second Atmosphere – Greenhouse gases:

• H2O, CO2, SO2

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The Importance of Earth’s Atmosphere on the Surface Temperature

• Heat input from Sun vs. Heat radiated by Earth. !

• This gives a temperature that is much smaller than the actual one – The Earth should be well below

freezing !

• Why is the Earth so warm? – The Greenhouse effect !

PTYS/ASTR 206 Earth 3/4/08

PTYS/ASTR 206

Earth 3/4/08

Greenhouse gases

• Molecules that absorb infrared radiation !

• Natural – Water Vapor H2O (most abundant) – Carbon Dioxide, CO2

– Methane, CH4

– Nitrous oxide, NO2 !

• Increased during industrial revolution – Carbon dioxide (CO2) – Methane (CH4) – Nitrous oxide (NO2) – Chlorofluorocarbons

Greenhouse effect -- results

• Earth is warmed up – With no Greenhouse Effect, average temperature would be below

freezing !

• Changing amount of Greenhouse Effect changes Earth’s temperature, weather – Changes not uncommon during Earth history – Usually changes what species are present – Details almost impossible to predict

As these trees grow where do they get the bulk of their mass from?

Carbon Cycle• Carbon cycles through atmosphere, oceans,

rocks, living matter. • 1 gallon of gasoline = 100 tons of plant life • 1 year of fuel consumption = ~500 years of plant

life

Climate Records– Sediment cores – Ice cores

• Temperature • Abundance of greenhouse gasses

Ice Cores

Effects of Melting Ice• Loss of sea ice

– Animal habitat (polar bear) – Northwest passage

• Melting grounded ice results in changes in sea level – Greenland Ice Sheet – Antarctic Ice Sheets

Atmospheric Circulation• Air flows from High pressure to Low pressure

– High pressure – moist warm air (equator) – Low pressure – cool dry air (poles) !

• Because the Earth spins we experience a Coriolis Effect. – This force is responsible for altering the path

of an object moving on a rotating object !!

!!!!!

Air currents without rotation ^

<- Air currents with rotation