Was ancient Earth a green planet?
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.