Scientists Date Land Plants Back 1.2 Billion Years

Two Arizona State University geologists say they have proof that land plants flourished near Phoenix 1.2 billion years ago, possibly challenging theories of climatic changes and evolution.

Rock samples collected by university geologists Paul Knauth and Mark Beeunas in the Sierra Ancha mountains about 100 miles east of Phoenix have confirmed the existence of the land plants.

Scientists have maintained that marine algae formed in oceans 3.5 billion years ago, but land plants did not appear for another 3 billion years.

“No one has ever denied there may have been some scummy form of land-plant life before then,” said Knauth. “It’s just that no one has found any evidence of it older than 400 millions years.”

The two geologists made their find about three years ago in a “miniature Grand Canyon,” at the Pendleton Mesa near Cherry Creek.

“We wanted to find an old exposure of a land surface to see if we could find any evidence of plants,” Knauth said. “This was one of the few examples of ancient land surface preserved in the rock record that we could put our hands on.”

More than 100 tests on the samples confirmed the presence of certain carbon isotopes that could have come only from land plants exhaling carbon dioxide into the soil as part of the photosynthesis process, he said.

The plants may have been nothing more than green slime, he noted.