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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
2ISP 205 - Astronomy Gary D. Westfall Lecture 9
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
3ISP 205 - Astronomy Gary D. Westfall Lecture 9
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
4ISP 205 - Astronomy Gary D. Westfall Lecture 9
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
5ISP 205 - Astronomy Gary D. Westfall Lecture 9
Plate TectonicsPlate Tectonics• Convection in the mantle causes movement of the
plates Plates pull apart along rift zones Plates come together at subduction zones
6ISP 205 - Astronomy Gary D. Westfall Lecture 9
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
7ISP 205 - Astronomy Gary D. Westfall Lecture 9
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
8ISP 205 - Astronomy Gary D. Westfall Lecture 9
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
9ISP 205 - Astronomy Gary D. Westfall Lecture 9
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
10ISP 205 - Astronomy Gary D. Westfall Lecture 9
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
11ISP 205 - Astronomy Gary D. Westfall Lecture 9
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
12ISP 205 - Astronomy Gary D. Westfall Lecture 9
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
13ISP 205 - Astronomy Gary D. Westfall Lecture 9
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
14ISP 205 - Astronomy Gary D. Westfall Lecture 9
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
15ISP 205 - Astronomy Gary D. Westfall Lecture 9
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
16ISP 205 - Astronomy Gary D. Westfall Lecture 9
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
17ISP 205 - Astronomy Gary D. Westfall Lecture 9
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