This is the VOA Special English SCIENCE REPORT.
A team of American and South African scientists has discovered evidence that life developed on land much earlier than experts had thought.
The researchers found fossil remains in South Africa that developed at least two-thousand-six-hundred-million years ago. They say that is more than one-thousand-four-hundred-million years earlier than had been thought. The publication Nature reported the findings.
Scientists believe that small organisms have lived in the Earth's oceans for about three-thousand-eight-hundred-million years. However, they are not sure when the first life forms appeared on land.
Until now, scientists believed fossils found in the American state of Arizona were the oldest proof of life on land. Those fossils are believed to be one-thousand-two-hundred-million years old.
The new study involved a seventeen-meter thick piece of rock from the South African province of Mpumalanga. The researchers say the rock is uncommonly rich in the element carbon.
Chemical tests suggest that the ancient fossils in the rock were bacteria called microbial mats. The microbial mats grew on the surface of the soil and then were buried while the soil was forming. The researchers say the microbial mats were about one centimeter thick. They are thought to be at least two-thousand-six-hundred-million years old.
The researchers say they also confirmed the presence of hydrogen, nitrogen and phosphorus in the rocks. The combination of the elements suggests a common biological link.
The researchers say their findings suggest that Earth's ozone layer and oxygen in the atmosphere existed two-thousand-six-hundred-million years ago. Both conditions are necessary for life to develop on land. Such a finding could support the idea that ozone could serve as a marker for the presence of life on other planets. Within twenty years, the American space agency NASA plans to launch a device. It would study the atmosphere of distant plants for such chemical markers.
Scientists from Pennsylvania State University led the research team. They received financial assistance for the study through a program supported by NASA. The researchers are now planning to explore Australia, Canada and other areas for evidence of ancient life.
This VOA Special English SCIENCE REPORT was written by George Grow.