Earth’s middle age marked by lack of tectonic activity

New Scientist : Between Earth’s formation, beginning some 4.5 billion years ago, and the present day, the planet has undergone amazing tectonic activity. However, that activity has not been constant throughout time: Beginning about 1.7 billion years ago, all geological processes appear to have stalled, and they remained so for a billion years. Tectonic activity only began to pick up again about 750 million years ago, when more complex life forms began to develop. Researchers have likened the evolutionary stall to a pot stewing on a stovetop: Early Earth was extremely hot and underwent dramatic changes, then got put on the back burner to simmer once the supercontinent of Rodinia formed; the mantle eventually cooled enough that modern subduction processes could kick in. That extended period of stability may have been vital for the development of eukaryotic cells, which are considered a milestone in the evolution of life.