Improbable Planet: How Earth Became Humanity's Home by Hugh Ross

Author:Hugh Ross
Language: eng
Format: mobi, epub
Tags: REL106000, REL067030
ISBN: 9781493405398
Publisher: Baker Publishing Group
Published: 2016-09-05T16:00:00+00:00

Figure 12.4. Pines and Fir Trees Eroding Cathedral Peak in Yosemite National Park [Credit: Hugh Ross]

2. Organic Carbon Burial

When photosynthetic life dies, decay processes break down its tissues (sugars, starches, fats, and cellulose) and release carbon dioxide back into the atmosphere—except when these tissues are buried before the decay processes can operate. If this burial is deep and enduring, such as when catastrophic floods and lava flows occur, it keeps the carbon dioxide from returning to the atmosphere and instead sequesters it in the crust. When crustal plates get subducted, the carbon dioxide can become sequestered for long periods of time in the mantle. Such events bring about a reduction in the quantity of atmospheric carbon dioxide.

Today the burial of life tissues is responsible for about 20 percent of the removal of carbon dioxide from Earth’s atmosphere. The erosion of exposed silicates accounts for the other 80 percent. Over the past billion years, however, this ratio has varied. At times, and as needed by life at those times, an alteration of this ratio resulted in greater or lesser compensation for the Sun’s increasing luminosity.

3. Atmospheric Composition

Different species of life either add to or subtract from the carbon dioxide, water, methane, oxygen, ozone, and aerosols in Earth’s atmosphere. Because carbon dioxide, water, and methane are greenhouse gases, their additions and subtractions alter atmospheric heat-trapping capacity. Aerosols tend to increase precipitation, which in turn boosts silicate erosion, which in turn decreases the quantity of carbon dioxide in the atmosphere. Most aerosols also tend to increase Earth’s albedo. Depending on the kinds and quantities of aerosols produced by various life-forms, the clouds reflect light (and its warming effect) away more or less effectively.

While the atmospheric proportions of carbon dioxide, water, methane, oxygen, and ozone help determine what species of life are possible and at what population levels, these species also influence the composition of the atmosphere. In other words, a certain ecosystem can alter the atmospheric chemistry so as to make possible the introduction of new life-forms, including those that are more efficient at removing greenhouse gases from the atmosphere.

4. Cloud Cover Variations

The different quantities of carbon dioxide, water, methane, oxygen, ozone, and aerosols that life adds to or subtracts from the atmosphere also determine the extent of Earth’s cloud cover and the characteristics of that cover. Certain types of clouds reflect light better than others. By reflecting away more sunlight, clouds can keep Earth’s surface at a temperature cool enough for life as the Sun brightens.

But cloud cover can create problems as well. If it proves too effective in blocking sunlight, cloud cover can stymie the growth of the life-forms most needed, such as photosynthetic bacteria and plants, to remove greenhouse gases from the atmosphere. Thus, to be sustained, life requires just-right kinds of clouds in just-right locations at just-right quantities and for just-right durations.

5. Change in Earth’s Albedo

The various species of life exhibit distinct colors and surface patterns. Some colors and patterns help absorb light while others reflect it away. Life’s colors and patterns alter the reflectivity of the oceans by only a little.

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