Earth’s Energy Cycle
Paragraph 1：To understand most of the processes at work on Earth, it is useful to envisage interactions within the Earth system as a series of interrelated cycles. One of these is the energy cycle, which encompasses the great “engines” — the external and internal energy sources—that drive the Earth system and all its cycles. We can think of Earth’s energy cycle as a “budget”: energy may be added to or subtracted from the budget and may be transferred from one storage place to another, but overall the additions and subtractions and transfers must balance each other. If a balance did not exist, Earth would either heat up or cool down until a balance was reached.
1. In paragraph 1, the author introduces the concept of a budget in order to
O indicate how different cycles in the Earth system relate to each other
O illustrate how Earth’s energy cycle must maintain an overall balance
O show that Earth gains energy from both external and internal sources
O explain how energy is transferred from one storage place to another
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