The fungus among us

Plants and fungi may have colonized the land much earlier than had been thought, according to scientists who say this could have had a major impact on climate and life on earth.

Researchers at Pennsylvania State University conducted the largest study to date of the genetics of plants, identifying mutations that occur on a regular basis and so could be used to trace the evolution of plants.

The analysis, published in the journal Science, indicates that land plants had evolved on earth about 700 million years ago, and land fungi had appeared about 1.3 billion years ago, which is much earlier than previous estimates of about 480 million years ago.

"We had no idea that fungi were quite so old," says S. Blair Hedges, who led the research team that conducted the study. "After finding land plants were so old, that took us to another question, which was: How could the presence of these land plants have affected land and climate?"

The researchers speculated that the findings could help explain what has been a mysterious lowering of the earth's surface temperature during a series of "snowball earth" events about 580 million to 750 million years in the past.

It could also explain the sudden appearance of many new species of animals during the Cambrian explosion about 539 million years ago. For example, the presence of plants, taking up carbon dioxide from the early atmosphere and adding oxygen to it, could have cooled the climate and had an impact on the further development of life, including the proliferation of animals, which need oxygen.

"We are proposing a biological explanation for these two seemingly unrelated phenomena, which before had geological explanations such as plate tectonics," says Dr. Hedges, an evolutionary biologist.

Linda Graham, a professor of botany at the University of Wisconsin in Madison, called the potential effect on climate "a reasonable speculation that just requires a great deal more work."