The author mentions outer space in line 6 because

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the Earth’s climate millions of years ago was similar to conditions in outer space.

it is similar to the ocean floor in being alien to the human environment

rock formations in outer space are similar to those found on the ocean floor

techniques used by scientists to explore outer space were similar to those used in ocean exploration

Giải thích

Đáp án B

Thông tin: " ....at the Earth’s surface, the deep-ocean bottom is a hostile environment to humans, in some ways as forbidding and remote as the void of outer space. Although researchers have taken samples of deep-ocean rocks and sediments for over a century, the first.."