2. EARTH AS A PLANET Chapter 7

3. SOME PROPERTIES of EARTH Semi major Axis1.00 AU Period1.00 year Mass5.98 x 10 24 kg Diameter12,756 km Escape Velocity112. Km/s Rotation Period23h 56m 4s Surface Area5.1 x 10 8 km 2 Atmospheric Pressure1.00 bar

4. EARTH as a PLANET l Only planet with water in liquid form. l Composition: iron, silicates, oxygen. l Density: highest in Solar System. l Interior: 4 major layers - core, outer core, mantle, crust.

5. EARTH as a PLANET l Only planet with water in liquid form. l Composition: iron, silicates, oxygen. l Density: highest in Solar System. l Interior: 4 major layers - core, outer core, mantle, crust. l Magnetic Field and Magnetosphere: Earth behaves as if it had a bar magnet inside it.

6. MAGNETOSPHERE and VAN ALLEN BELTS

7. The MAGNETOSPHERE SHAPE

8. EARTH’S STRUCTURE – HOW DO WE KNOW IT? FROM EARTHQUAKES

9. PLATE TECTONICS l Earth’s crust consists of about 12 plates.

10. PLATE TECTONICS l Energy escaping from the interior drives the plates (few cm/year). 50 million years from now

11. PLATE TECTONICS l Where plates interact, dramatic changes occur in Earth’s crust. ä Rift Zones: Plates pulling apart. Material rises from mantle to fill spaces (volcanoes). E.g.. Mid Atlantic Ridge.

12. PLATE TECTONICS l Where plates interact, dramatic changes occur in Earth’s crust. ä Subduction Zone: Two plates come together, once forced down and melts. Earthquakes and volcanoes common along subduction zones.

13. PLATE TECTONICS l Coastal BC is on the upper part of a subduction zone.

14. SAN ANDREAS FAULT

15. ACTIVE SITES on EARTH’S SURFACE

17. CONTINENTAL DRIFT

18. FLASHCARDFLASHCARD AT 2 CM/YEAR, HOW LONG WOULD IT TAKE A TYPICAL PLATE TO TRAVERSE THE PRESENT WIDTH OF THE ATLANTIC OCEAN, ABOUT 6000 KM? A) 3 X 10 6 YR B) 1.2 X 10 7 YR C) 3 X 10 8 YR D) 1.2 X 10 9 YR

19. < 10 km, most atmosphere here. (N 2 78%, O 2 21%, Ar 1%, traces H 2 O, CO 2 )Troposphere 10 - 80 km, cold (-50ºC), cloudlessStratosphere 50 - 80 km, O3, absorbs UV radiationOzoneLayer Atmosphere very thin, constant leakage of H and He > 100 km

20. GREENHOUSE EFFECT l CO 2 content of atmosphere is critical for its role in retaining heat from Sun. l Greenhouse Effect: ä Earth absorbs sunlight and re-emits it as infrared (IR) radiation (Earth acts like a blackbody). ä CO 2 transparent to sunlight but absorbs IR acting like a blanket. ä The more CO 2, the hotter Earth is.

21. GREENHOUSE EFFECT and GLOBAL WARMING l Greenhouse effect has raised Earth’s average temperature by 23ºC. l Without the greenhouse effect, Earth’s average temperature would be below freezing and Earth would be in a constant global ice age.

22. GREENHOUSE EFFECT and GLOBAL WARMING l CO 2 levels are increasing. l Prediction: rising CO 2 levels will lead to global warming with uncertain consequences.

23. THE MOON l 1/4 the size of Earth

24. THE MOON l Earth’s Moon has no atmosphere.

25. THE MOON l The Moon is tidally locked to Earth. Non rotating Moon Rotating Moon

26. THE MOON l Only extraterrestrial object that humans have visited.

27. APOLLO MISSIONS

28. MOON’S INFLUDENCE on EARTH l Differential forces on Earth tend to stretch Earth slightly.

29. TIDAL BULDGES in an “IDEAL” OCEAN

30. SPRING and NEAP TIDES

32. MOON’S INFLUDENCE on EARTH l Tidal friction slowly is increasing the length of Earth’s day. (6 hours 4.5 billion years ago, 22 hours 620 million years ago)

33. LIFE on EARTH l Earth is the only planet known to be harbouring life. l Life arose early on. Fossils date back 3.5 billion years. ä Origin of life is unsure. ä Miller experiment: produced amino acids and other pre-biological molecules from primitive Earth atmosphere - mainly CO 2 (No O 2 ).

34. LIFE on EARTH l Development of plants: l Formation of the ozone (O 3 ) layer ä Use up CO 2 and produce O 2 - photosynthesis. ä Free O 2 in atmosphere 2 billion years ago. ä Protects Earth from UV. ä This allowed life to leave protective oceans and colonize the land. Not possible earlier.

35. COSMIC INFLUENCES on EARTH’S EVOLUTION l Moon is heavily cratered - caused by impacts. ä Where are Earth’s craters? ä Most lost by erosion and geological activity.

36. COSMIC INFLUENCES on EARTH’S EVOLUTION l More than 150 impact craters are still recognized on Earth’s surface.

37. COSMIC INFLUENCES on EARTH’S EVOLUTION l Concern is that a large object, ≥10 km, will collide with Earth releasing a few billion times as much energy as Hiroshima bomb.

38. COSMIC INFLUENCES on EARTH’S EVOLUTION l Concern is that a large object, 10 km, will collide with Earth releasing a few billion times as much energy as Hiroshima bomb. l One such object crosses Earth’s orbit every 100 million years.

39. ORBITS of the 100 LARGEST KNOWN NEAR-EARTH ASTEROIDS

40. IMPACT FREQUENCY Impactors on the surfce of the space shuttle 1  m, 30  sec Shooting stars 1 mm, 30 sec Meteroites 1m, 1yr Arizona Crater 100 m, 10 4 yr Sudbury, Ontario 10 km, 10 8 yr

41. COSMIC INFLUENCES on EARTH’S EVOLUTION l More than 150 impact craters are still recognized on Earth’s surface. METEOR CRATER ä 0.1 km meteor ä Crater size = 10 x size of impacting object 1.2 km

42. TUNGUSKA EVENT Siberia June 30, 1908 Projectile exploded before impacting Earth

43. Projectile’s mass estimated to be 100,000 tons Caused widespread damage.

44. TUNGUSKA EVENT

45. SHOEMAKER-LEVI COMET

46. IMPACTIMPACT Earth’sViewVoyager’sView

47. SHOEMAKER-LEVI IMPACT

48. DEVELOPMENT of DUST CLOUD Impact

49. IMPACT DUST CLOUDS

50. IR IMAGE of IMPACTS Io

51. COSMIC INFLUENCES on EARTH’S EVOLUTION con’t

52. EFFECTS of a MASSIVE IMPACT

53. ä Huge tidal waves. ä Dust high up in the atmosphere. ä Block out Sun for about one year, kills photosynthesis. ä World-wide fires, forests and grasslands destroyed. ä Highly acidic rains. ä Animals depending on plants die (dinosaurs?), rise of mammals. ä Global earthquakes.

54. EXTINCTIONS, the SOLAR SYSTEM and our GALAXY l Past 100 million years many large scale extinctions (~ 10) identified on Earth. äIn these, a significant fraction of existing species were extinguished. l Best known is extinction of the dinosaurs 65 million years ago after flourishing for 100 million years.

55. EXTINCTIONS, the SOLAR SYSTEM and our GALAXY ä äImpact of ~ 20 km asteroid. ä äEvidence: crater in Gulf of Mexico and Iridium layer. l What caused the extinctions?

56. EXTINCTIONS, the SOLAR SYSTEM and our GALAXY l What caused the extinctions? ä äImpact of ~ 20 km asteroid. ä äEvidence: crater in Gulf of Mexico and Iridium layer. ä äNearby supernova (depletes O 3, forming NO 2 ). Crab Nebula

57. EXTINCTION of the DINOSAURS

59. ALTERNATE DINOSAUR EXTINCTION THEORY

60. EXTINCTIONS, the SOLAR SYSTEM and our GALAXY l Supernovae and impacts more likely when Sun passes through spiral arm in our Galaxy äOort cloud comets get perturbed.

61. SPIRAL GALAXY

62. OORT CLOUD GETS PERTURBED