What is the main source of energy that drives the earth's systems?

Main source of energy that drives the earth's systems is Sun.

Explanation:

The Sun drives all the Earth's systems and makes life possible on this planet with a tremendous amount of energy that it releases. Apart from warming the Earth, the Sun also maintains the hydrologic cycle.

The sunlight reaching the earth is absorbed by the land surfaces, all the water bodies, and atmosphere while at the same time, some of the energy is reflected by the ice and the clouds into space.

When the Earth emits the same amount of energy that the Sun does, a balance is maintained in the average temperature of the planet. The Earth's climate is determined by the amount of sunlight that is received from the Sun and changes in the latter will cause a significant difference in the climate and weather; depending on this factor, the earth will either be warm or cool.

i'm sure the answer you are looking for would be

a. an ice age

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