Two prominent scientists update our view of the history of life on Earth, featuring the prominent roles of oxygen and carbon dioxide, and question claims that it is fairly easy to initiate life—even on a planet such as ours
Contrary to popular belief, humans continue to evolve. Our bodies and brains are not the same as our ancestors' were—or as our descendants' will be
Changes in the shells of these nautliuslike marine animals at the end of their long history suggest they were fighting a losing battle against more mobIle, shell-crushing predators
The animal trims its weight and gains mobility by dividing its shell into compartments and removing their watery content. It succeeds in spite of the ocean's pressure, which tends to drive water back in
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![Life Ain't Easy: What Would Make an Exoplanet "Earth-Like"? [Excerpt]](/sciam/cache/file/70250F80-EA46-40E4-86583E667AEBA5D1_small.jpg)
