isp 205 - astronomy gary d. westfall1lecture 9 earth as planet the earth is a medium size planet...

1ISP 205 - Astronomy Gary D. Westfall Lecture 9

Earth as PlanetEarth as Planet

• The Earth is a medium size planet with a diameter of 12,756 kilometers (7926 miles)

• Composed primarily of iron, silicon, and oxygen

• Nearly circular orbit and just the right distance from the Sun Water not boiled away or frozen

• No hydrogen or helium in the atmosphere Hydrogen bound in water


Earth’s InteriorEarth’s Interior• The Earth’s interior has been studied using seismic

waves Waves produced by earthquakes, impacts, explosions

• Crust 6 km thick basalt under oceans 20 - 70 km thick granite under continents

• Mantle Solid, extends to a depth of 2900 km

• Core Diameter of 7000 km, iron, nickel

• Inner core Diameter of 2400 km, dense and solid


Earth’s Magnetic FieldEarth’s Magnetic Field• Earth’s magnetic field is approximately aligned with the

geographic poles• The Earth’s magnetic field traps charged particles from the Sun’s

solar wind Magnetosphere Causes aurora borealis


The Earth’s CrustThe Earth’s Crust• Crust is composed of various kinds of rock

Igneous - volcanic Sedimentary - deposited by wind or water Metamorphic - changed by temperature/pressure

• Primitive rock exists in the form of comets and asteroids but not on Earth

All the material on Earth was once molten

• The crust is broken up into pieces called that float on the mantle

Plate tectonics


Plate TectonicsPlate Tectonics• Convection in the mantle causes movement of the

plates Plates pull apart along rift zones Plates come together at subduction zones


Results of Plate TectonicsResults of Plate Tectonics

The San Andreas Fault, the boundary between the Pacific Plate and the American Plate

Liquid lava reaches the ocean in Hawaii above a rift zone in the ocean floor

The Alps are uplifted by the African plate bumping into Europe


Structure of the Earth’s AtmosphereStructure of the Earth’s Atmosphere• The atmosphere does not have much mass compared with

the entire Earth• The atmosphere is usually divided into layers• Troposphere

Most of the atmosphere is within 10 km of the surface of the Earth

• Stratosphere Top of the stratosphere is the ozone

layer (O3)

• Mesosphere• Ionosphere

Air molecules are ionized by UV from Sun

Reflect AM and longer radio waves


Composition of Earth’s AtmosphereComposition of Earth’s Atmosphere• Earth’s atmosphere consists of

78% nitrogen (N2)

21% oxygen (O2) 1% argon (Ar) Traces of

water vapor (H2O)

Carbon dioxide (CO2)

• The Earth’s atmosphere today is not the same as it was originally

May have been formed as the Earth formed May have been released from the interior after Earth formation May have come from impacts of comets Dramatically influenced by the onset of living things


Origin of Life and the Earth’s AtmosphereOrigin of Life and the Earth’s Atmosphere

• A key step in the evolution of life on Earth was the development of blue-green algae

Consumed CO2 and gave off O2

Photosynthesis

• Free O2 began accumulating in the Earth’s atmosphere about 2 billion years ago

• The ozone layer formed then giving protection from UV Living things could leave the oceans

• Life and the presence of water produced a dramatic decrease in CO2

• Decaying living things produced the nitrogen in Earth’s atmosphere


Evidence for Life 3 Billion Years AgoEvidence for Life 3 Billion Years Ago• Before the Earth’s atmosphere had oxygen and the

resulting ozone layer that absorbs UV, all life had to exist in the safety of the ocean

• In these pictures, blue algae is fossilizes in rocks dating back 3 billion years


Weather and ClimateWeather and Climate• Weather is caused by the uneven

heating of the Earth by the Sun and by the rotation of the Earth

• Climate refers to long term trends in weather

The last ice age ended 14,000 years ago after lasting for 20,000 years

2 km thick over Boston and extended to New York City

Shaped Michigan’s topology


The Greenhouse Effect and Global WarmingThe Greenhouse Effect and Global Warming

• CO2 is a greenhouse gas• Sunlight of all wavelengths passes the atmosphere,

is absorbed by the surface and radiated as infrared

• CO2 is opaque to infrared and traps the infrared radiation, warming the Earth Current greenhouse gasses warm the Earth 23C

• CO2 is increasing due to man Burning of fossil fuels Destruction of forests

• More CO2 could cause global warming Complex problem


COCO22 in Earth’s Atmosphere in Earth’s Atmosphere• Measured at Mauna Loa, Hawaii

CO2 measurements showing seasonal variations and plotted with suppressed zero

Same CO2 measurements showing seasonal variations

and plotted without a suppressed zero


COCO22 in Earth’s Atmosphere 2 in Earth’s Atmosphere 2• Taken from air trapped in ice in Antarctica

CO2 measurements for the past 1000 years plotted with a suppressed zero

CO2 measurements for the past 1000 years plotted without a

suppressed zero


Cosmic Influences on the Evolution of EarthCosmic Influences on the Evolution of Earth• We observe that other planets have been struck by

meteors• We observe craters on these planets• Craters on Earth are erased by the active geology and be

weather• There are 100 known craters on Earth


A Large Event 65 Million Years AgoA Large Event 65 Million Years Ago• The map below show the location of the buried

crater from an impact event 65 million years ago


Earth as TargetEarth as Target• As we will see,

there are many objects in the solar system that potentially could collide with the Earth

• The picture on the right shows a computer simulation of what the Earth would look like if Comet Shoemaker-Levy hit the Earth near East Lansing

isp 205 - astronomy gary d. westfall1lecture 9 earth as planet the earth is a medium size planet...

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