t’s a question that goes back decades: If other civilizations have arisen beyond Earth over the course of billions of years, why haven’t we heard from them? Two kinds of answers have recently come into the spotlight – one kind that’s disheartening, and another kind that’s challenging.
First, the bad news: Researchers from the Australian National University say climate change could have killed off E.T. and his ilk.
In a paper published last month in the journal Astrobiology, Aditya Chopra and Charles Lineweaver suggest that habitable Earthlike planets eventually fall prey either to runaway global warming, as in the case of Venus; or runaway global cooling, as in the case of Mars.
Their model proposes that if life ever does arise on an alien world, it would go extinct in most cases after just 1.5 billion years of the planet’s existence, without getting past the microbial stage.
