A 50-million-year fossil record of ammonoids includes two kind of the nautilus-like creatures, swimmers and floaters. At two points of mass extinction, the swimming ammonoids disappear completely from the fossil record.
Credit: Brown University
MARYLAND: Two of the greatest mass extinctions in Earth's history may have been caused by the loss of diversity in the oceans. New research shows that the die-off of species may have ultimately led to the collapse of marine ecosystems.
The study could be an ominous warning for the future of life on Earth as modern ocean diversity begins to dwindle. Conservation biologists regularly note the precipitous decline of key species, such as cod, bluefin tuna, swordfish and sharks.
Lose enough of these top-line predators (among other species), and the fear is that the oceanic web of life may collapse.
Took 10 million years to repopulate
In a new paper in Geology, researchers at Brown University, Rhode Island, and the University of Washington used a group of marine creatures similar to today’s nautilus to examine the collapse of marine ecosystems that coincided with two of the greatest mass extinctions in the Earth’s history.
They attribute the ecosystems’ collapse to a loss of enough species occupying the same space in the oceans, called ‘ecological redundancy.’ While the term is not new, the paper marks the first time that a loss of ecological redundancy is directly blamed for a marine ecosystem’s collapse in the fossil record.
Just as ominously, the authors write that it took up to 10 million years after the mass extinctions for enough variety of species to repopulate the ocean – restoring ecological redundancy – for the ecosystem to stabilise.
Serves as a cautionary tale
“It’s definitely a cautionary tale because we know it’s happened at least twice before,” said lead author Jessica Whiteside, assistant professor of geological sciences at Brown. “And you have long periods of time before you have reestablishment of ecological redundancy.”
If the theory is true, the implications could not be clearer today. According to the United Nations-sponsored report Global Biodiversity Outlook 2, the population of nearly one-third of marine species that were tracked had declined over the three decades that ended in 2000.
The numbers were the same for land-based species. “In effect, we are currently responsible for the sixth major extinction event in the history of the Earth, and the greatest since the dinosaurs s disappeared, 65 million years ago,” the 2006 report states.
Mass extinctions
This story seems to be putting the cart before the horse. Loss of diversity IS a mass extinction. There is no logic here whatsoever. I thought there was already conclusive evidence that meteor strikes were responsible for most mass extinctions. Volcanoes come a close second. In fact the 256million year old mass extinction of the age of Amphibians appears to have been caused by both a Meteor strike and from Vulcanism. As both the 480km crater in Wilkes land, Antarctica and the 12,000 foot thick lava flows of the Siberian traps are both 256million years old, one begins to wonder at the coincidence. Both these sites were directly opposite each other 256 million years ago. As volcanoes cannot cause meteor impacts, it seems far more likely that the meteor impact caused the vulcanism - vulcanism without a volcano. The most likely place for rupturing of the earths crust, would not be where the energy is dissipating from, but where the energy from the impact converges again - on the opposite side of the planet. The 5,000 foot thick Deccan is 65million years old and was directly opposite the 300km Chixculub crater in the Yucatan that has been attributed to the most famous mass extinction - of the dinosaurs. Yes catastrophes do occur, don't be fooled into thinking 'benign gradualism' is the answer to all the riddles on this planet.