Official 21 Passage 1
Question 1 of 14

According to the processes described in paragraph 1, what is the relationship between radioactivity and the steam produced by geothermal heat?


Geothermally heated steam is produced when water is exposed to radioactivity deep underground.


When water is introduced into holes drilled thousands of feet in the ground, it becomes radioactive and turns to steam.


Radioactivity heats Earth’s interior rock, which in turn can heat water to the point it becomes steam.


When a reservoir of steam in subsurface rock is produced by radioactivity, it is said to be geothermally heated.

Paragraph 1 is marked with an arrow




Geothermal Energy

[#paragraph1]Earth’s internal heat, fueled by radioactivity, provides the energy for plate tectonics and continental drift, mountain building, and earthquakes. It can also be harnessed to drive electric generators and heat homes. Geothermal energy becomes available in a [#highlight2]practical[/highlight2] form when underground heat is transferred by water that is heated as it passes through a subsurface region of hot rocks (a heat reservoir) that may be hundreds or thousands of feet deep. [#insert1] The water is usually naturally occurring groundwater that seeps down along fractures in the rock; less typically, the water is artificially introduced by being pumped down from the surface. [#insert2] The water is brought to the surface, as a liquid or steam, through holes drilled for the purpose. [#insert3]

[#paragraph2]By far the most [#highlight3]abundant[/highlight3] form of geothermal energy occurs at the relatively low temperatures of 80° to 180° centigrade. [#insert4] Water circulated through heat reservoirs in this temperature range is able to extract enough heat to warm residential, commercial, and industrial spaces. More than 20,000 apartments in France are now heated by warm underground water drawn from a heat reservoir in a geologic structure near Paris called the Paris Basin. Iceland sits on a volcanic structure known as the Mid-Atlantic Ridge. Reykjavik, the capital of Iceland, is entirely heated by geothermal energy derived from volcanic heat.

[#paragraph3]Geothermal reservoirs with temperatures above 180° centigrade are useful for generating electricity. They occur primarily in regions of recent volcanic activity as hot, dry rock; natural hot water; or natural steam. The latter two sources a