Answer to Question 1
Earth's atmosphere became oxygen rich about 2.5 billion years ago and fundamentally changed Earth's ability to support life. Increased atmospheric oxygen caused the ozone concentration in the upper atmosphere to build up, thereby shielding Earth's surface from ultraviolet radiation. This effectively eliminated the food supply for anaerobic bacteria. Oxygen is also highly reactive with organic matter. When anaerobic bacteria are exposed to oxygen and light, they are killed instantaneously. By 1.8 billion years ago, the atmosphere's oxygen content had increased to such a high level that it began causing the extinction of many anaerobic organisms. Because aerobic respiration releases nearly 20 times more energy than anaerobic respiration aerobic respiring organisms were able to thrive.
Answer to Question 2
Warm-water vents have water temperatures below 30C (86F) and generally emit water that is clear in color. White smokers have water temperatures from 30 to 350C (86 to 662F) and emit water that is white because of the presence of various light-colored compounds, including barium sulfide. Black smokers have water temperatures above 350C (662F) and emit water that is black because of the presence of dark-colored metal sulfides, including iron, nickel, copper, and zinc.
Evolution Humor
Titan's dense atmosphere shrouds the moon beneath a tan haze in this image.
Photosynthetic Organisms Changed Earth's Atmosphere
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Earth Atmosphere
Time Line for Life’s Origin and Evolution