Which of the following best describes the earth's average surface temperature for the past 900,000 years? A. a steady warming trend B. fairly steady temperatures until recently C. prolonged periods of cooling and warming D. fairly steady with occasional cool spells E. fairly steady with a recent cooling trend

Option (C)

Explanation:

The earth undergoes episodic and prolonged warming and cooling events depending on its distance from the sun. The temperature on earth is directly dependent on the amount of incoming solar radiations and the amount of radiations reflected back from earth into space, which is to be in equilibrium in order to maintain a suitable earth's temperature. When there occurs increasing or decreasing temperature, it eventually leads to the warming and cooling of the earth. According to Milankovitch, the earth cools and warms on approximately 100,000 years because of changing position with respect to the sun.

Thus, the correct answer is option (C).

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