A VAST submarine eruption 93 million years ago may have suffocated life in Earth鈥檚 oceans.
In the middle of the Cretaceous period, the planet鈥檚 oceans spent nearly half a million years starved of oxygen, which caused the extinction of 27 per cent of marine invertebrates. Such 鈥渁noxic events鈥� have happened several times in the past, usually when soaring atmospheric carbon dioxide levels spark rampant global warming and a rise in ocean bioproductivity. This creates extra organic matter that is then consumed by aerobic bacteria, which remove oxygen from the water to do so.
It has long been thought that the eruption of massive flood basalts injected all that CO2, but it has never been proved. Now, Steven Turgeon and Robert Creaser of the University of Alberta, in Edmonton, Canada, believe they have found the smoking gun: osmium isotopes.
Advertisement
Osmium has two isotopes: osmium-187 and osmium-188. Seawater contains roughly equal numbers of each, but magma has more osmium-188. Turgeon and Creaser found more osmium-188 in sedimentary rocks deposited during the mid-Cretaceous, suggesting submarine lavas were present in sufficient quantity to alter the chemical signature of the water (Nature, vol 454, p 323).
