It's generally thought that the evolution of complex life was a rare, once-in-4.5-billion-years event.
But new research suggests that conditions were right for complex cells to evolve and die off at least once - or perhaps several times - before our lineage even got started. Billions of years ago, there could have been other complex life forms on the planet, totally unrelated to anything we see on Earth today. Earth has been around for an estimated 4.5 billion years.
However, most of the archaeological evidence of an ancient civilization would probably have been lost.
Complex life might have come and gone on Earth long before the multicellular organisms we're familiar with today arose, a new study suggests.Now the stargazer has said advanced aliens may have left behind “technosignatures” for us to find — if only we knew where to look for them.“A prior indigenous technological species might have arisen on ancient Earth or another body, such as a pre-greenhouse Venus or a wet Mars,” he wrote.In the , study author Adam Frank describes the research in an opinion piece titled, "Yes, There Have Been Aliens." Drake's famous equation measures the odds that advanced civilizations are out there and broadcasting their presence.It comes down to (R*) the number of stars born each year that (f) are technologically advanced enough to release detectable signals into space? Selector .selector_input_interaction .selector_input. Selector .selector_input_interaction .selector_spinner.