New Haven, Conn. — The murky world at the bottom of the oceans is now a little clearer, thanks to a new study that tracks the evolution of marine sediment layers across hundreds of millions of years.

It is a story of world-building on a grand, yet granular, scale, accomplished by a succession of marine animals that burrowed and tunneled their way through heat and cold, species expansions and mass die-offs. Scientists call the process bioturbation — the excavation and mixing of sediments and soils by burrowing animals, particularly for shelter and sustenance.

“Bioturbation is one of the most important forms of ecosystem engineering today, both in the oceans and on land,” said Lidya Tarhan, assistant professor of Earth and planetary sciences in Yale’s Faculty of Arts and Sciences, and lead author of the study published in the journal Science Advances.

Using geochemical analyses of marine sediments, researchers have been able to quantitatively reconstruct the Atlantic Meridional Overturning Circulation over the past 12,000 years. An international research team, led by scientists from Heidelberg University and the University of Bern (Switzerland), is the first to calculate the large-scale circulation patterns of the Holocene. Their reconstruction shows that, while the AMOC experienced natural fluctuations over millennia, it remained stable for long periods of time.