Mean atmospheric O2
Geologic Time Scale
Land plants of the species Cooksonia caledonica, the only witness to a spectacular Late Silurian sunset 425 million years ago, establish a tenuous foothold on a mound of ancient lava.
Over 400 million years ago the first plants emerged from the waters and made the Earth's surface their home. They were simple plants, standing only a few inches tall, consisting of slender stalks with branches and rounded structures called sporangia. The sporangia, common to funguses and non-seed plants today, produced and contained the spores required for reproduction.
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