(OrganicJar) Earth’s landmasses in the late Precambrian probably weren’t pleasant, but at least they were green. A new analysis of limestone rocks laid down between 1 billion and 500 million years ago suggests that there was extensive plant life on land much earlier than previously thought.
The plants were only tiny mosses and liverworts, but they would have had a profound effect on the planet. They turned the hitherto barren Earth green, created the first soils and pumped oxygen into the atmosphere, laying the foundations for animals to evolve in the Cambrian explosion that started 542 million years ago.
It was already known from genetic evidence that mosses and liverworts probably evolved around 700 million years ago, but up till now there was little sign that they had colonized land to any great extent. The assumption was that terrestrial life consisted of patchy bacterial mats and “algal scum” until the mid-Ordovician, 475 million years ago, when land was first invaded by modern-looking vascular plants.
Paul Knauth of Arizona State University and Martin Kennedy of the University of California, Riverside, examined the chemical composition of all known limestones dating from the Neoproterozoic era, which stretched from 1 billion years ago up to the start of the Cambrian. Knauth says the balance of carbon-12 to oxygen-18 in the limestones is “screaming” that they were laid down in shallow seas that received extensive rainwater run-off from a land surface thick with vegetation.
Snowball Earth Theory
Some scientists don’t agree, as there is little fossil evidence. Paul can explain this, by the snowball Earth theory, which says that the very late Neoproterozoic Earth suffered an ice age so extensive that there were glaciers in the tropics. If this is correct, plants would have been obliterated soon after colonising the land. Knauth, however, says that few people now believe the “hard” version of the theory, and that the glaciations were less severe than once thought. This “slushball Earth” allows for extensive ice free regions, so land plants could have survived.
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