The "boring billion," the long evolutionary pause when slime ruled the Earth, might be due to a planetary cooling-off period that stalled plate tectonics, a new study suggests.
The so-called boring billion refers to the span from 1.7 billion years to 750 million years ago when algae and microbes had the run of Earth. Why boring? The long pause comes after these single-celled creatures mastered photosynthesis, meaning they could absorb energy from the sun instead of munching rocks and metal. After that extraordinary leap, there was little evolutionary advancement for another billion years, until the first complex life emerged.
Scientists have long sought an explanation for this big hold-up. Now, researchers think they've found a possible cause: the planet itself. It turns out plate tectonics also had a boring billion, according to research presented last week at the annual Goldschmidt geochemistry conference in Sacramento, California. The findings were also published in the June 2014 issue of the journal Geology.
Study authors Peter Cawood and Chris Hawkesworth of the University of St. Andrews in Scotland looked at how the continents behaved in the past by analyzing indicators of tectonic activity such as volcanic eruptions, global glaciations and giant gold and sulfur deposits. The continents weren't the same size through time, nor did they plow across the planet at the same speed. They found the continents grew quickly on the early Earth, had a stable middle age and are now entering a midlife crisis. [In Images: How North America Grew as a Continent]
"We are going from a time when you didn't destroy much crust to a time when you do," Hawkesworth said.
The transition from stability to destruction, which marks an uptick in tectonic motion, took place 750 million years ago, the same time as the emergence of complex life.