Enlarge A mysterious cycle of booms and busts in marine biodiversity over the past 500million years could be tied to a ‘pulse of the Earth’ – a periodic uplifting of continents that results in the seas being too shallow for species to survive in, according to a new study.
Researchers at the University of Kansas believe evidence for these uplifts lie in the increased amounts of an element found in the continental crust that they’ve subsequently detected in marine fossils whenever mass extinctions have occurred.
The fact that the element, strontium-87, is suddenly appearing in the oceans means that there must have been sudden huge tectonic movements that the researchers believe played havoc with marine life.
Adrian Melott, a Professor of Physics and Astronomy at the University of Kansas , said: ‘Strontium-87 is produced by radioactive decay of another element, rubidium, which is common in igneous rocks in continental crust.
So, when a lot of this type of rock erodes, a lot more Sr-87 is dumped into the ocean, and its fraction rises compared with another strontium isotope, Sr-86.’
An uplifting of the continents, Melott explains, is the most likely explanation for this type of massive erosion event.
‘Continental uplift increases erosion in several ways,’ he said. ‘First, it pushes the continental basement rocks containing rubidium up to where they are exposed to erosive forces. Uplift also creates highlands and mountains where glaciers and freeze-thaw cycles erode rock.
‘The steep slopes cause faster water flow in streams and sheet-wash from rains, which strips off the soil and exposes bedrock. Uplift also elevates the deeper-seated igneous rocks where the Sr-87 is sequestered, permitting it to be exposed, eroded, and put into the ocean.’
The massive continental uplift suggested by the strontium data would also reduce sea depth along the continental shelf where most sea animals live. …