Chemical signatures in shale rocks, a consolidated form of mud, point to an increased rate in the rise of land above the ocean 2.4 billion years ago—possibly triggering dramatic changes in climate and life.
Chemical signatures in shale rocks, a consolidated form of mud, point to an increased rate in the rise of land above the ocean 2.4 billion years ago—possibly triggering dramatic changes in climate and life.
In a study published in the journal Nature, researchers from six universities, including the University of Chicago, report that shales sampled from around the world contains archival-quality evidence of fleeting, almost imperceptible traces of rainwater that caused weathering of land as old as 3.5 billion years ago.
The exposure of new land to weathering may have set off a series of glacial episodes and atmospheric changes spawned by the Great Oxygenation Event, in which free oxygen filled the air, said University of Oregon geologist Ilya Bindeman, who led the study.
The evidence is from analyses of three oxygen isotopes, particularly the rare but stable oxygen-17, in multiple shale samples from every continent and spanning 3.7 billion years of Earth's history. Shale rocks are formed by the weathering of crust, so "they tell you a lot about the exposure to air, light and precipitation,” Bindeman said.
Read more at University of Chicago
Photo: The composition of ancient shales shows that about 2.4 billion years ago, the pattern of precipitation changed as rainwater fell over larger continents and higher mountains. CREDIT:Basil Greber
