GRE Reading Comprehension: JiJing 352-GRE阅读机经352篇 - 65O54YG5574BDC6RK

A team of researchers has claimed that by drilling below the Earth's surface, they have been able to recover microorganisms that inhabit depths where it was previously thought that no life existed. Although other microorganisms that were at first thought to have been recovered from these depths were later determined merely to have come from surface soil, that cannot be so in this case, because ________.