Carl Zimmer in Sequencer Magazine:
Some of the microbes that rose from the ocean fell on land instead of water. Lying on the bare continents, they no longer had sea water to shield them from direct sunlight. Many likely died as the ultraviolet radiation ravaged their genes and proteins. Meanwhile, the atmosphere was sucking out the water from their interiors, causing their molecules to stick together and collapse into toxic shapes.
Over time, however, life adapted to land. The earliest signs of its spread are 3.2-billion-year-old fossils from South Africa. They preserve microbial mats that grew in a braidplain of streams woven across an arid landscape. The water in the streams would have periodically dried up, exposing the mats to dry air. Mutations that helped the microbes survive longer out of water would have allowed them to reproduce more, shaping future generations. Instead of relying on water to shield them, these microbes grew pigments that could absorb the deadly ultraviolet rays. They also relied on cooperation to survive in the air. Terrestrial microbes worked together to build rubbery films around themselves. These biofilms soaked up rain and water vapor from the air and held onto it during dry weather.
Three billion years later, these living films still exist. Known as biological soil crusts, they can be as thin as butter on toast, or as thick as the toast itself. Biological soil crusts today cover about 12 percent of dry land—roughly equivalent to the area of South America.
More here.
Enjoying the content on 3QD? Help keep us going by donating now.