Us & E.T.

Tim Radford reviews two new books about the possibility of extraterrestrial intelligence:

Perhaps life is frequent, but intelligence is highly improbable. Or perhaps all competitive, technological civilisations discover thermonuclear weapons, and destroy themselves. Maybe the rest of the galaxy is keeping a vow of silence, leaving us either to obliterate ourselves or grow up enough to join the federation.

Here on Earth, life began within the first billion years, but complex life required another 3.8 billion years to make a primate. In 5 billion years, the sun will flare up and incinerate planet Earth, but life's tenure will have ended long before that, perhaps 500 million years from now, as carbon dioxide levels fall to near zero, plants perish and the seas begin to boil away. To survive, tomorrow's Earthlings must find somewhere else to live. E.T., presumably, faces the same pressure.