Ancient Algae Could Survive on Our Terrestrial Planet Before Leaving the Water

Scientists may have solved a long-running mystery about the first stages of plant life on Earth. They found that our planet was once covered with a film of ancient alga that was able to inhabit land before it went on to evolve in the world's first plant.

Before now, researchers assumed that the alga evolved the capability to source essential nutrients for its survival after it arrived on land by forming a close association with a beneficial fungi called arbuscular mycorrhiza (AM), which still exists today. This fungi helps plant roots obtain nutrients and water from soil in exchange for carbon. This latest study, though, shows that this may not be the case.

The researchers analyzed DNA and RNA of some of the earliest known land plants and green algae. This revealed that their shared algal ancestor living in the Earth's waters already possessed the set of genes needed to detect and interact with the beneficial AM fungi. This capability, in particular, was probably pivotal in enabling the alga to survive out of the water and to colonize the Earth. By working with the fungi to find sustenance, the alga was able to buy time to adapt and evolve in a very different environment.

"At some point 450 million years ago, alga from the Earth's waters splashed up on to barren land," said Pierre-Marc Delaux, one of the researchers, in a news release. "Somehow it survived and took root, a watershed moment that kick-started the evolution of life on Earth. Our discovery shows for the first time that the alga already knew how to survive on land while it was still in the water. Without the development of this pre-adapted capability in alga, the Earth could be a very different place today."

The findings are published in the journal Proceedings of the National Academy of Sciences.

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