Scientists still don't know what caused the changes to the continental crusts
at the time, but think there is a link to modern plate tectonics, which began around the same time.
"According to the current theory, the first continental crusts
were formed when tectonic plates would collide, submerging oceanic crusts into the earth's mantle, where they would partially melt at a depth of approximately 100 kilometres.
This atlas of migmatites, heterogeneous rocks often found in continental crusts
, is designed for geologists and mineralogists who need a reference for identifying and classifying these substances in the field.
Volcanoes most often form on or near tectonic plate boundaries, regions where Earth's nine continental crusts
converge (see map).
In early earth history, igneous rocks derived from the mantle were progressively assembled and accreted to form continental crusts
. Subsequent collision of continental blocks and arcs produced mountains and yielded new sediments.
For the purpose of the study, the researchers - Peters and his postdoctoral fellow at the University of Wisconsin-Madison Jon Husson - studied the history of sediment accumulation on continental crusts
and compared it to the history of atmospheric concentration.