Long before there were humans, aliens were thriving on Earth. That’s according to a new study. New research suggests that complex life may have evolved on Earth much earlier than scientists originally thought. Though scientists have long agreed that the evolution of complex life can only occur once every 4.5 billion years, new research could transform our understanding. Researchers at the University of Washington have suggested that complex life forms evolved and died on this planet before the current lineage even began.
Earth is believed to be 4.5 billion years old. 3.7 billion years ago, bacteria and archaea began to evolve. These single-celled organisms thrived on the planet for billions of years until eukaryotes began to emerge. The eukaryote family tree eventually comprised all complex organisms including plants, birds, and mammals. Though scientists are not certain how the eukaryote kingdom came into being, a popular theory is that ancient bacteria ingested archaea, forming a symbiotic relationship that eventually became the mitochondria visible in the cells of complex organisms.
It has long been presumed that oxygen was brought to Earth by the excretions of cyanobacteria over billions of years. Complex life could have only developed when there was an explosion of oxygen in our atmosphere. Scientists have long believed the level of oxygen in our atmosphere reached sustainable levels 1.6 billion years ago.
In the new study, researchers analyzed the layers of ancient deposits of selenium. They discovered that there was enough oxygen in the Earth’s atmosphere between 2.4 and 2 billion years ago to support complex life. After that brief time period, oxygen levels dropped off suddenly—an occurrence that’s cause is unknown at this time. But the discovery means conditions to support complex life forms were evident on the planet long before eukaryotes were evident on the planet.
“The oldest fossil is not necessarily the oldest one that ever lived because the chances of getting preserved as a fossil are pretty low,” astrobiologist Roger Buick said. “This research shows that there was enough oxygen in the environment to have allowed complex cells to have evolved, and to have become ecologically important before there was fossil evidence. That doesn’t mean that they did—but they could have.”
The discovery is potentially groundbreaking, indicating that the chance that life has developed on planets other than Earth is significantly more likely than was once thought.