¨ Section 6

Atmospheric Oxygen

http://www.rgbstock.com/bigphoto/noG3LtC/Sky,+Sea+Background+2

Learning Targets:

•I can describe transitions the Earth has gone through and scientific reasons why.

•I can explain evidence from the deep past that is used to inform us about today’s conditions on Earth.http://www.ianknauer.net/DSFWork/wordpress/a-fresh-look-at-energy-2/cutting-greenhouse-gases/atmosphere/

51. A stable climate is only one key requirement for the complex life forms that populate Earth today.

52. Multi-cellular organisms also need a ready supply of oxygen for respiration.

53. Today oxygen makes up about 20 percent of Earth's atmosphere, but for the first two billion years after Earth formed, its atmosphere was anoxic (oxygen-free).

http://www.google.com/search?q=Multi-cellular+organisms&hl=en&qscrl=1&rlz=1T4RNQN_enUS489US489&tbm=isch&tbo=u&source=univ&sa=X&ei=iEIaUseMGMLc2QXl2IDwDg&ved=0CEcQsAQ&biw=1455&bih=703#facrc=_&imgdii=_&imgrc=M7q-Hhnfb3r6AM%3A%3B41AWaAhh2u4mtM%3Bhttp%253A%252F%252Fwww.gambassa.com%252Fgambassafiles%252Fimages%252Fimages%252F1425%252Fmulticellular_organisms_v1.jpg%3Bhttp%253A%252F%252Fwww.gambassa.com%252Fpublic%252Fproject%252F2554%252FSarahButler'sGeologicTimeline.html%3B500%3B400

54. Oxygen is a highly reactive gas that combines readily with other elements like hydrogen, carbon, and iron. Many metals react directly with oxygen in the air to form metal oxides. For example, rust is an oxide that forms when iron reacts with oxygen in the presence of water.

http://fantasystock.deviantart.com/art/Metal-Rust-Texture-05-58746146

Section 7 Early Life: Single-Celled Organisms pp. 19-21

http://www.prescottcreeks.org/blog/amanda-richardson/2011/06/28/when-do-bacteria-our-surface-waters-present-public-health-risk

55. There is clear evidence that life existed at least 3 billion years ago, and the oldest sediments that have been discovered—rocks formed up to 3.8 billion years ago—bear marks that some scientists believe could have been left by primitive microorganisms.

http://www.sciencedaily.com/releases/2008/07/080710094033.htm

56. Life on Earth existed for many millions of years without atmospheric oxygen.

57. Paleontologist Andrew Knoll stated, "Bacteria, not mammals, underpin the efficient and long-term functioning of the biosphere".

http://www.dailygalaxy.com/my_weblog/2013/07/oxygen-were-the-building-blocks-of-earths-atmosphere-from-elsewhere-in-the-galaxy.html

58. Microorganisms are still part of Earth's chemical cycles, but most of the energy that flows through our biosphere today comes from photosynthetic plants that use light to produce organic material.

http://www.tumblr.com/tagged/aquatic-plants