Scientists have found the best evidence yet that plants appeared on land about 475 million years ago, 50 million years earlier than fossils had established before.

　　While spores dating back about 475 million years had already been found, it had not been proven whether they came from land or aquatic plants. In the new study, the spores were found with the spore sac that produced them, indicating they came from a land-based plant, said study author Charles Wellman of the University of Sheffield in England.

　　The oldest fossils of land plants themselves are about 425 million years old and the age discrepancy between the oldest spores and the oldest fossils has puzzled scientists.

　　"Now, we've actually got the spores in the plants," said Wellman, whose paper appears in today's issue of the journal Nature.

　　"I've found the spores lots of times, but I've never found the actual plants that produce the spores."

　　The spores and plant matter were discovered by sieving through core samples drilled in the search for oil, in this case a 1,485-meter-deep core drilled in northern Oman. Wellman's group dissolved the rock in a type of acid that does not destroy organic matter, and then strained the acid to find the spores and plant fragments.

　　Plants are believed to have made their way onto land before animals.

　　Paul kenrick, an early plant researcher at London's Natural History Museum, says the latest findings won't completely silence skeptics.

　　The research, however, tilts the scales in favor of those who say the 475 million-year-old spores came from land-based plants.

　　Others have said the oldest land-based plants may be as much as 700 million years old, based on a genetic analysis of when the genomes of land and aquatic plants diverged.

　　The latest work helps narrow the age estimates, and shows scientists what size the earliest plants were - tiny.

　　"If you were walking about on Earth back then, to see anything at all you would have been on your hands and knees with hand lens," Kenrick said. "Sort of like Sherlock Holmes, looking through a magnifying glass at all of these things.

　　"Life was on a completely different scale," Kenrick said.