About 570 million years ago, life on Earth was limited to the depths of the oceans. At that time, large, unusual invertebrate organisms firmly anchored themselves to the seafloor, using their fleshy appendages to collect nutrients passing by. These unique life forms, known as the Ediacaran biota, eventually went extinct. However, scientists have long debated whether their disappearance was the result of a catastrophe.
In January, a new study published in the journal Geology suggests a reevaluation of the scale of the extinction event known as the Avalon crisis. The study indicates that this event may have been much more significant than previously thought, wiping out approximately the same percentage of species as the asteroid-induced catastrophe that killed the dinosaurs 66 million years ago.
Although the Avalon crisis led to fewer extinct organisms compared to the Great Extinction that occurred about 252 million years ago, "in terms of the percentage of extinct animals, this event is comparable to later counterparts," claims Shuhai Xiao, a paleobiologist from Virginia Tech who was not involved in the study. This finding helps clarify our incomplete understanding of the rare Ediacaran biota.
The study focuses on Ediacaran creatures from a fossil collection known as the Avalon assemblage. This collection includes the earliest large and complex organisms found in the paleontological record. These soft-bodied creatures were first discovered on the Avalon Peninsula in Newfoundland in 1958 and inhabited deep-sea areas between 574 and 560 million years ago.
These early ecosystems included a variety of organisms, from lichens to giant clusters of bacteria, representing a completely extinct realm of life that no longer exists on Earth, says Lydia Tarhan, a paleontologist from Yale University who did not participate in the study. "Debates continue about what type of animals they should be classified as."
According to fossil data, around 560 million years ago, a minor extinction occurred in the Avalon community, paving the way for a more diverse group of organisms known as the White Sea community. This group, in turn, experienced a more significant extinction about 10 million years later, known as the Avalon crisis.
According to Duncan MacIlroy, a paleontologist from Memorial University of Newfoundland and the lead author of the study, the Avalon crisis was the first major mass extinction event that animals ever experienced. Previous studies indicate that about 65% of all species went extinct as a result of this event.
In this work, MacIlroy and his team present recently discovered fossils from the Inner Meadow site in Newfoundland. This site preserved at least 19 genera of Ediacaran organisms, including many branching filter feeders also found in other well-known layers of Avalon.
"When we removed the moss and soil on the first day, it became clear that this was a unique place," shares MacIlroy. "The fossils were beautifully preserved, and many of them had not been weathered."
Using small fragments of uranium zircon formed from ancient ash deposits, MacIlroy and his colleagues applied uranium dating methods to establish that the new fossils are about 551 million years old. "This is significantly younger than most previous estimates," notes Tarhan.
This discovery suggests that the animals from the Avalon assemblage existed 10 million years longer than previously thought and went extinct during the Avalon crisis, rather than earlier, as was previously believed, due to a less significant extinction event.
The data indicate that the Avalon crisis, which occurred 550 million years ago, was more devastating than previously assumed. According to MacIlroy, instead of 65% extinction of species, additional data suggest a loss of about 80%—enough to qualify the crisis as a mass extinction. Thus, the Avalon crisis became "a very significant event in the history of the animal kingdom," he concludes.
"I was amazed," says MacIlroy about the new dates. "In science, sometimes new data or ideas resonate so widely that they leave you dizzy; I'm not sure I slept much that first night."
MacIlroy suggests that future excavations in the Inner Meadow and other locations in Newfoundland may lead to discoveries of new victims of the Avalon crisis. "There are many new genera and species that are still waiting to be described," he says.
Tarhan notes that the new data is "exciting." "Fossil complexes of the Ediacaran biota are quite rare in the world," she emphasizes, adding that reevaluating this data provides important clues about the history of the Ediacaran period.
The reasons for the death of animals during the Avalon crisis remain a mystery. MacIlroy believes that the most likely cause is an ecological crisis, although there are other hypotheses, including a sudden drop in ocean oxygen levels or high predation activity by early cnidarians, the ancestors of modern jellyfish. "We will only be able to figure this out through further research," he adds.
The post The First Major Extinction on Earth Turned Out to Be Worse Than We Thought appeared first on K-News.
