The tree that changed the world.

Fossilized hunks of wood found recently in Morocco are repainting the picture of Earth's earliest woody tree, which transformed the planet more than 370 million years ago.

The extinct plant Archaeopteris lived during the late Devonian period, when amphibians were just beginning to crawl onto land. Previous studies of this spore-producing tree suggested that Archaeopteris grew only deciduous branches that dropped off after a year or two, a growth pattern that limited the tree's lifetime.

In 1998, a team of scientists traveled to the Sahara Desert and collected over 150 fossils of Archaeopteris, including a 5-meter-long section of trunk. These fossils showed that Archaeopteris had thick permanent branches as well as the short-lived kind, report Brigitte Meyer-Berthaud of the University of Montpellier II in France, Stephen E. Scheckler of the Virginia Polytechnic Institute and State University in Blacksburg, and Jobst Wendt of Tubingen University in Germany. They describe their finds in the April 22 NATURE.

This kind of branching structure indicates that Archaeopteris lived longer than previously thought, perhaps up to 50 years, says Scheckler. The thick permanent branches would also have increased the shade produced, thereby cooling off the streams where amphibians were rapidly evolving.

As Archaeopteris spread across the globe, it pulled carbon dioxide out of the atmosphere and turned down the planet's thermostat. At the same time, it pumped oxygen into the air, helping to set the stage for land vertebrates. "In the beginning of the Devonian, we would not have been able to breathe without apparatus, but by the end of the Devonian, we would have been able to breathe," says Scheckler.