basic words --- 5

新学期なので基本的な言葉からはじめましょう。

species, evolution, speciation, extinction, biological diversity(=biodiversity)

上記の語を含む以下の文章を読んでみましょう。生物では基本的な知識なのではないでしょうか。

  The fact that millions of species are in existence today is evidence that speciation has clearly kept well ahead of extinction. In spite of the fact that there have been numerous periods of mass extinction, there is clear evidence that periods of mass extinction have been followed by periods of dramatic increases in new species to fill the void created by the mass extinctions, though it may take 10 million years or more following a mass extinction for biological diversity to be rebuilt through speciation. When the dinosaurs disappeared 65 million years ago, for example, the evolution and speciation of mammals increased spectacularly over the millions of years that ensued.

文法・語法的な問を一つ。上記の文で下線をほどこしたthatはそれぞれどのような役割を果たしているthatですか。