In the past, there have always been events in which a large part of life on Earth died out. Now here is the prime suspect.
Bloomington – Since the origin of life on Earth, there have always been phases in which some life has been destroyed again. The most famous example is probably the asteroid impact that wiped out the dinosaurs and numerous other animal species 66 million years ago. But such events have happened before: the Devonian era saw several mass extinctions in which experts estimate that nearly 70 percent of life on Earth disappeared.
The Devonian began about 419 million years ago and ended about 358 million years ago – at which time life had not spread from the oceans to land. Now scientists have discovered how the numerous mass extinctions in the Devonian could have happened: tree roots are said to be to blame.
Tree roots could lead to mass extinctions
“It’s not easy to look back more than 370 million years,” says Matthew Smart, who was Filippelli’s student at the time of the study. “However, rocks have long memories, and there are still places on Earth where you can use chemistry like a microscope to reveal the mysteries of the past.” Scientists therefore analyzed rock deposits in ancient riverbeds, examined levels of phosphorus – a chemical element found in all life on Earth – and soil formation.
“Our analysis shows that the development of tree roots in the past likely flooded the oceans with excess nutrients, leading to massive algae growth,” Indiana University biogeochemist Gabriel Filippelli said in a statement. The expert continues: “These rapid and destructive algal blooms would deplete most of the oxygen in the oceans and trigger catastrophic mass extinctions.”
The process is similar to today’s “dead zones” in the sea
The process the researchers used in their study, published in the journal Bulletin of the Geological Society of America published, is similar to a process that can be observed today on a smaller scale: In the Gulf of Mexico, for example, there are wide “dead zones” – areas that are virtually devoid of oxygen. There, excess nutrients from fertilizers and agricultural waste 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: whereas then tree roots were responsible, now people are responsible. Fortunately, modern trees no longer cause such destruction because nature has now developed systems to compensate for the effects of decaying wood, says Filippelli. The depth of modern soil also retains more nutrients than the thin layer of dirt that once covered the ground.
Still, the scientists 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 caused by human activity today,” Fillipelli points out. (bookmark)