Rivers then transported the calcium, magnesium, and carbonic acid into the oceans where the calcium, magnesium—and also the carbon dioxide—came together to form insoluble limestone.
In searching for an answer, Pogge von Strandmann and co-authors, including first author Alex Krause, began analyzing 40-million-year-old oceanic carbonates and clay minerals to compare the results with those for similar 56-million-year-old examples. Negative emissions technologies such as this involving the absorption of carbon dioxide are the subjects of intense research across the globe. At the same time, however, if the weathering results in the formation of clay, the effects of the process would be significantly less efficient, as Pogge von Strandmann has discovered. Clay retains the calcium and magnesium that would otherwise be delivered to the ocean.