The mass extinction that Earth is currently experiencing is the seventh, not the sixth, as previously thought.
This is what the results of a new scientific study concluded, during which researchers discovered a mass extinction that was unknown to scientists, when the planet lived more than half a billion years ago.
The study, published in the Proceedings of the National Academy or Science, known as PNAS, confirmed that the discovered mass extinction occurred after the first complex multicellular life forms appeared on the planet, and was accompanied by a decrease in the percentage of Oxygen in the oceans for unknown reasons.
The last mass extinction occurred 66 million years ago and wiped out the dinosaurs (Getty Images)
5 known mass extinctions
Since the emergence of life on its surface, the Earth has witnessed a number of dramatic events, in the wake of which a large proportion of the organisms disappeared.
According to a report published on the New Atlas website, the planet has witnessed at least 5 mass extinctions, each of which wiped out more than 70% of life.
The first occurred about 450 million years ago at the end of the Ordovician period, with the disappearance of approximately 85% of marine life at that time.
The most important mass extinction occurred at the end of the Permian period 250 million years ago when 96% of all living species including ocean vertebrates and land animals disappeared.
The last of these occurred at the end of the Cretaceous period 66 million years ago, and wiped out nearly 75% of plants and animals, including dinosaurs.
But the occurrence of other extinctions, especially before the first known extinction, remained a possibility for paleontologists because it was difficult to obtain evidence to prove this.
The sixth mass extinction occurred about 550 million years ago (Shutterstock)
The discovery of the sixth extinction
In the new study, scientists from UC Riverside and Virginia Tech found evidence of a sixth mass extinction that occurred about 550 million years ago, about 100 million years before the earliest known mass extinction.
This period is known as the Ediacaran period, corresponding to the emergence of multicellular organisms.
Nearly 80% of all living organisms in that era disappeared within 10 million years as a result of environmental changes, according to a press release posted on the University of California Riverside website on November 22.
Those beings were strange and unlike any being living now.
Among them were Obamus Coronatus, a disc-shaped creature named after former President Barack Obama, and Attenborites janeae, a small, oval, raisin-like creature.
Although previous studies had indicated a decrease in the diversity of life in this early period, they did not conclude that a mass extinction occurred due to the limited fossil record.
But the database the researchers created in this study, which collected all known fossil evidence from this period, supported the hypothesis of a mass extinction of life, especially since the percentage of organisms lost is similar to the percentages recorded in other similar events.
The mass extinction at the end of the "Ediacaran" period occurred due to the lack of oxygen availability in the ocean (Getty Images)
Low oxygen in the oceans
The researchers noted that all the organisms that survived the extinction had a common feature: their bodies had a large surface area despite their small size.
It is a property known to help animals tolerate low oxygen conditions, enabling them to obtain more nutrients.
Since there is geochemical evidence that oxygen decreased 550 million years ago, and that these organisms did not move far from their habitats, the study authors concluded that the Ediacaran period may have ended with a mass extinction due to the lack of oxygen availability in the ocean.
Although it is not clear why oxygen levels dropped so sharply at the end of that era, environmental changes, such as those occurring now due to pollution and global warming, could destabilize and destroy life on Earth at any time.
These changes have been behind all mass extinctions, including the current one, say the researchers.