In the past there have always been events in which large parts of life on earth died out. Now there is a prime suspect.
Bloomington – Since the emergence of life on earth, there have always been phases in which part of life has been destroyed again. The best-known example is probably the Asteroid Impact that the Dinosaurs and numerous other animal species died out 66 million years ago. But such events have happened before: in the Devonian era there were several mass extinctions in which experts estimate that almost 70 percent of life on Earth disappeared.
The Devonian began about 419 million years ago and ended about 358 million years ago – at that time life had not spread from the oceans to land. Now researchers have found out how the numerous mass extinctions in the Devonian could have come about: tree roots are said to be to blame.
Tree roots may have led to mass extinctions
“It’s not easy to look more than 370 million years into the past,” says Matthew Smart, who was a student of Filippelli at the time of the study. “But stones have a long memory and there are still places on earth where you can use chemistry as a microscope to unveil the mysteries of the past.” The researchers therefore analyzed rock deposits in old river beds, examined phosphorus levels – a chemical one Element found in all life on earth – and soil formation.
“Our analysis shows that the development of tree roots has likely flooded the oceans with excess nutrients in the past, leading to massive algal growth,” explains biogeochemist Gabriel Filippelli of Indiana University in one Message. The expert continues: “These rapid and destructive algal blooms would have depleted most of the oxygen in the oceans and triggered catastrophic mass extinctions.”
Process is similar to today’s “dead zones” in the sea
The process that the researchers used in their study in the journal Geological Society of America Bulletin released was described is similar to a process that can be observed today on a smaller scale: for example, in the Gulf of Mexico there are broad “Dead Zones” – Areas that are virtually devoid of oxygen. There, excess nutrients from fertilizers and agricultural runoff trigger massive algal blooms that use up all the oxygen in the water.
However, the difference between the process in Devon and today is huge: while tree roots were responsible then, people are now. Fortunately, modern trees no longer wreak similar destruction, as nature has now developed systems to offset the effects of decaying wood, Filippelli says. The depth of modern soil also retains more nutrients than the thin layer of dirt that used to cover the earth.
Nevertheless, the researchers issue a warning: “These new findings about the catastrophic consequences of natural events in the past can serve as a warning about the consequences of similar conditions that are caused by human activities today,” emphasizes Fillipelli. (tab)