Earth

1. Earth • Third planet from the Sun • Fifth largest • Orbit: 149,600,000 km (1.00 AU) • Diameter: 12,756 km • Mass: 5.972 X 1024 kg

2. Not until Copernicus (16th century) was it understood that Earth is just another planet.

3. Interior • Divided into several layers which have distinct chemical and seismic properties (depths in km): • 0 - 40 Crust Outside Radius = 6378 • 40 - 400 Upper mantle Outside Radius = 6338 • 400 - 2700 Lower mantle • 2700 - 5150 Outer core Outside Radius = 3678 • 5150 - 6378 Inner core Outside Radius = 1228

5. General Characteristics • Crust varies in thickness - thinner under the oceans - thicker under continents • Inner core and crust are solid. • Outer core and mantle layers are plastic or semi-fluid. • Layers are separated by discontinuities which are evident in seismic data; • The Mohorovicic discontinuity between the crust and upper mantle, for example.

7. Inner Core • Likely a solid • Composed mostly of iron (or nickel/iron) with few other lighter elements. • Temperatures at the center are ~7500 Kelvin • Hotter than the surface of the Sun.

8. Outer Core • Likely a fluid • Composed mostly of iron (or nickel/iron) with few other lighter elements. • Temperatures cooler than inner core.

10. Lower Mantle • The lower mantle is mostly… • Silicon, • Magnesium • Oxygen • with some… • Iron, • Calcium, & • Aluminum.

11. Upper Mantle • The upper mantle is mostly… • Olivene and Pyroxene (iron/magnesium silicates), and • Calcium and Aluminum.

14. How do we know about the interior? • Most knowledge about the interior comes from… • studying seismic waves but there are also samples of rock and magma that have… • come to the Earth’s surface from below.

15. Crust • Granite in the continents is made mostly of quartz (silicon dioxide) and feldspar while... • basalt in the oceans is made mostly of minerals with lots of iron and magnesium.

17. Chemical Composition of Earth • Proportion by mass: • 34.6% Iron • 29.5% Oxygen • 15.2% Silicon • 12.7% Magnesium • 2.4% Nickel • 1.9% Sulfur • 0.05% Titanium

18. Distribution of Mass on Earth • Most is in the mantle followed by core. (values below are x10^24 kilograms): • Atmosphere = 0.0000051 • Oceans = 0.0014 • Crust = 0.026 • Mantle = 4.043 • Outer core = 1.835 • Inner core = 0.09675

21. Planet Comparison • Earth is the densest major body in the solar system. • The other terrestrial planets have similar structures and compositions with some differences:

22. Differences • Moon has a small core, maybe none. • Mercury has an extra large core (relative to its diameter); • Mantles of Mars and the Moon are much thicker; • Moon and Mercury may not have chemically distinct crusts; • Earth may be the only one with distinct inner and outer cores. • Remember that our knowledge of planetary interiors is mostly theoretical even for the Earth.

23. Plate Tectonics • Crust is divided into several separate solid plates • Float around independently on top of the hot mantle. • Unique to the solar system.

25. Plate Tectonics • Characterized by two major processes:

26. Plate Tectonics • Sea floor spreading - two plates move away from each other and new crust is created by upwelling magma from below.

28. Plate Tectonics • Subduction - two plates collide and the edge of one dives beneath the other and ends up being destroyed in the mantle.

30. Plate Tectonics • Unique boundaries: • Transform/Transverse Motion: the San Andreas Fault in California • Convergent: Collisions - India/Eurasia forming the Himalayas • Divergent: pulling apart (sea-floor spreading)

31. Eight Major Plates (Currently): • North American Plate - North America, western North Atlantic and Greenland • South American Plate - South America and western South Atlantic • Antarctic Plate - Antarctica and the "Southern Ocean" • Eurasian Plate - eastern North Atlantic, Europe and Asia except for India • African Plate - Africa, eastern South Atlantic and western Indian Ocean • Indian-Australian Plate - India, Australia, New Zealand and most of Indian Ocean • Nazca Plate - eastern Pacific Ocean adjacent to South America • Pacific Plate - most of the Pacific Ocean (and the southern coast of California!)

34. Plate Tectonics • Twenty or more small plates such as the Arabian, Cocos, and Philippine Plates. • Earthquakes are much more common at the plate boundaries. • Plotting locations makes it easy to see the plate boundaries.

36. Continental Drift Animation

38. Age of Earth Surface • Very young… • ½ billion years • Erosion and tectonic processes destroy and recreate most of the surface. • Eliminates traces of earlier geologic history (such as impact craters). • The very early history of the Earth has mostly been erased.

39. Age of Earth • 4.5 to 4.6 billion years old • Oldest known rocks are about 4 billion years old • Rocks older than 3 billion years are rare. • Oldest fossils of living organisms are ~3.9 billion years old. • No record of the critical period when life was first getting started.

40. Water • Covers 71 % of surface. • Only on Earth can it be in liquid form • (Although, there may be liquid methane on Titan's surface and liquid water beneath the surface of Europa). • Essential for life as we know it. • Ocean heat capacity keeps the Earth's temperature relatively stable. • Responsible for erosion and weathering of the Earth's continents • (a process unique in the solar system today, though it may have occurred on Mars in the past).

41. Atmosphere • 77% nitrogen, • 21% oxygen, • & traces of… • argon, • carbon dioxide, and water.

42. CO2 • Large amount of carbon dioxide in the past • Has… • Incorporated into carbonate rocks, • dissolved into the oceans, and • consumed by living plants. • Plate tectonics and biological processes now maintain a flow of CO2 from the atmosphere to these various processes.

43. Greenhouse Effect • CO2 in the atmosphere maintains surface temperature. • Raises average surface temperature about 35° C above what it would otherwise be. • From a frigid -21°C (-6°F) to a comfortable +14°C (57°F) • Oceans would freeze and life would be impossible. • Water vapor is also an important greenhouse gas.

44. Free Oxygen • Presence is rare from a chemical point of view. • A very reactive gas under “normal” circumstances; it would quickly combine with other elements. • Produced and maintained by biological processes. • Stromatolites were believed to be first creators of oxygen. • Without life there would be no free oxygen.

46. Tidal Effects • Earth-Moon tidal interaction slows the Earth's rotation by 2 milliseconds per century. • 900 million years ago, there were 481 18-hour days in a year.

47. Magnetic Field • Modest in size • Produced by electric currents in the outer core. • Interacts with the solar wind to produce aurora. • Irregularities cause magnetic poles to move and reverse relative to the surface. • Geomagnetic north pole is currently located in northern Canada.