AREAS of open water may have provided a vital haven for life on Earth when
the rest of the planet froze over about 700 million years ago.
One nagging question about the 鈥渟nowball Earth鈥� theory has been how early
animals could have survived if a thick ice sheet covered the entire planet
(New 杏吧原创, 6 November 1999, p 28).
Photosynthesis would have been impossible in the dark, ice-covered oceans,
so creatures should have starved. But using a simulation that includes ice-sheet dynamics,
William Hyde of Texas A&M University has shown that stretches of open water might
have remained near the equator (Nature, vol 405, p 425). He calls his model a
鈥渘别补谤-蝉苍辞飞产补濒濒鈥�.