
Green algae grow at the edges of a glacial lake in Wales. Hundreds of millions of years ago, similar algae adapted to survive temporarily outside of the water may have kicked off the evolution of green land plants.
Around 500 million years ago — when the Earth was already a ripe 4 billion years old — the first green plants appeared on dry land. Precisely how this occurred is still one of the big mysteries of evolution. Before then, terrestrial land was home only to microbial life. The first green plants to find their way out of the water were not the soaring trees or even the little shrubs of our present world. They were most likely soft and mossy, with shallow roots and few of the adaptations they would later evolve to survive and thrive on dry land. And though scientists agree that these plants evolved from some kinds of seaweed, we know comparatively little about those green algal ancestors.
But a few recent papers — two based on molecular biology, and one on rare, precious fossils from 1 billion years ago — are helping to fill in the gaps in our understanding of those ancient algae and what allowed them to eventually make the transition to land.














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