ISP Astronomy Gary D. Westfall1Lecture 9 Earth 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 n Water not boiled away or frozen No hydrogen or helium in the atmosphere n Hydrogen bound in water

ISP Astronomy Gary D. Westfall2Lecture 9 Earth’s Interior The Earth’s interior has been studied using seismic waves n Waves produced by earthquakes, impacts, explosions Crust n 6 km thick basalt under oceans n km thick granite under continents Mantle n Solid, extends to a depth of 2900 km Core n Diameter of 7000 km, iron, nickel Inner core n Diameter of 2400 km, dense and solid

ISP Astronomy Gary D. Westfall3Lecture 9 Earth’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 n Magnetosphere n Causes aurora borealis

ISP Astronomy Gary D. Westfall4Lecture 9 The Earth’s Crust Crust is composed of various kinds of rock n Igneous - volcanic n Sedimentary - deposited by wind or water n Metamorphic - changed by temperature/pressure Primitive rock exists in the form of comets and asteroids but not on Earth n All the material on Earth was once molten The crust is broken up into pieces called that float on the mantle n Plate tectonics

ISP Astronomy Gary D. Westfall5Lecture 9 Plate Tectonics Convection in the mantle causes movement of the plates n Plates pull apart along rift zones n Plates come together at subduction zones

ISP Astronomy Gary D. Westfall6Lecture 9 Results 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

ISP Astronomy Gary D. Westfall7Lecture 9 Structure 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 n Most of the atmosphere is within 10 km of the surface of the Earth Stratosphere n Top of the stratosphere is the ozone layer (O 3 ) Mesosphere Ionosphere n Air molecules are ionized by UV from Sun n Reflect AM and longer radio waves

ISP Astronomy Gary D. Westfall8Lecture 9 Composition of Earth’s Atmosphere Earth’s atmosphere consists of n 78% nitrogen (N 2 ) n 21% oxygen (O 2 ) n 1% argon (Ar) n Traces of u water vapor (H 2 O) u Carbon dioxide (CO 2 ) The Earth’s atmosphere today is not the same as it was originally n May have been formed as the Earth formed n May have been released from the interior after Earth formation n May have come from impacts of comets n Dramatically influenced by the onset of living things

ISP Astronomy Gary D. Westfall9Lecture 9 Origin of Life and the Earth’s Atmosphere A key step in the evolution of life on Earth was the development of blue-green algae n Consumed CO 2 and gave off O 2 n Photosynthesis Free O 2 began accumulating in the Earth’s atmosphere about 2 billion years ago The ozone layer formed then giving protection from UV n Living things could leave the oceans Life and the presence of water produced a dramatic decrease in CO 2 Decaying living things produced the nitrogen in Earth’s atmosphere

ISP Astronomy Gary D. Westfall10Lecture 9 Evidence 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

ISP Astronomy Gary D. Westfall11Lecture 9 Weather 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 n The last ice age ended 14,000 years ago after lasting for 20,000 years n 2 km thick over Boston and extended to New York City n Shaped Michigan’s topology

ISP Astronomy Gary D. Westfall12Lecture 9 The Greenhouse Effect and Global Warming CO 2 is a greenhouse gas Sunlight of all wavelengths passes the atmosphere, is absorbed by the surface and radiated as infrared CO 2 is opaque to infrared and traps the infrared radiation, warming the Earth n Current greenhouse gasses warm the Earth 23  C CO 2 is increasing due to man n Burning of fossil fuels n Destruction of forests More CO 2 could cause global warming n Complex problem

ISP Astronomy Gary D. Westfall13Lecture 9 CO 2 in Earth’s Atmosphere Measured at Mauna Loa, Hawaii CO 2 measurements showing seasonal variations and plotted with suppressed zero Same CO 2 measurements showing seasonal variations and plotted without a suppressed zero

ISP Astronomy Gary D. Westfall14Lecture 9 CO 2 in Earth’s Atmosphere 2 Taken from air trapped in ice in Antarctica CO 2 measurements for the past 1000 years plotted with a suppressed zero CO 2 measurements for the past 1000 years plotted without a suppressed zero

ISP Astronomy Gary D. Westfall15Lecture 9 Cosmic 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

ISP Astronomy Gary D. Westfall16Lecture 9 A Large Event 65 Million Years Ago The map below show the location of the buried crater from an impact event 65 million years ago

ISP Astronomy Gary D. Westfall17Lecture 9 Earth 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