Humans Are Not Alone, Ancient Alien Worlds May Have Existed

The existence of alien life is not just a belief, but a probability, after the discovery of exoplanets. Perhaps alien civilizations existed long ago, according to scientists.

"The question of whether advanced civilizations exist elsewhere in the universe has always been vexed with three large uncertainties in the Drake equation," said Adam Frank of the University of Rochester and co-author of the new study. "We've known for a long time approximately how many stars exist. We didn't know how many of those stars had planets that could potentially harbor life, how often life might evolve and lead to intelligent beings, and how long any civilizations might last before becoming extinct."

It has been found by NASA's Kepler satellite and other planetary searches that about one-fifth of stars in the universe have planets in the "habitable" zone. In this zone, the temperatures can support life as we know it, but it is more interesting how civilizations may inhabit the habitable planets.

"The fact that humans have had the rudimentary technology for roughly ten thousand years doesn't really tell us if other societies would last that long or perhaps much longer," Frank said.

Calculating the odds against the existence of life in the cosmos, scientists found that human life might be unique only if the odds of a civilization growing in a habitable planet are less than about one in 10 billion trillion. That works out to just one part in 10 to the 22nd power.

"One in 10 billion trilling is incredibly small," Frank said. "To me, this implies that other intelligent, technology producing species very likely have evolved before us. Think of it this way. Before our result, you'd be considered a pessimist if you imagined the probability of evolving a civilization on a habitable planet were, say, one in a trillion. But even that guess, one chance in a trillion, implies that what happened here on Earth with humanity has in fact happened about 10 billion other times over cosmic history!"

The findings were published on April 22, 2016, issue of the journal Astrobiology.