Millions of years in the past, during the early days of living organisms, an extinction-level event suffocated organisms, which paved the way for vertebrates to conquer the world.
When we hear mass extinctions, we often believe that there are brief moments in history that wreaked havoc devastating but momentary. However, the Devonian extinction, the second of the so-called "Big Five" mass extinction events, defy that notion.
While other great die-offs are often instantaneous and short-lived, the Devonian extinction laid waste to the Earth periodically throughout 25 million years, killing three-quarters of all species. But, despite its destruction, it also paved the way for vertebrates and a new balance of animal life that persists until today.
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Devonian Extinction
Beginning about 380 million years ago, halfway through the geological time known as the Devonian period or the age of fish where vertebrates have yet to leap onto land. Prehistoric waters were teeming with life, but not of tuna, salmons, and sardines that we know today; in fact, these waters were filled with the ancestors of these species.
The top of the food chain was dominated by placoderms, a species of heavily-armored fish. The most famous is the Dunleosteus, which may have grown up to 30 feet long. Despite their reputable size and physique, they were not able to survive past age.
Michael Coates, a biologist from the University of Chicago, says, "a ser5ies of crises piled up to affect life on Earth." Annihilation slowly crept in and swept away dominant Devonian species due to the crises. These events opened ecological niches to a new array of organisms.
Thomas Algeo from the University of Cincinnati explains that the Devonian extinction differs from other mass-extinction events in terms of time frame. Throughout millions of years, there have been 10 distinct events that equated with the loss of biodiversity. Two stand out: the Hangenberg and Kellwasser events that occurred in the middle and at the end of the Devonian era, respectively.
Definitive answers are rare when it comes to extinction. However, researchers agree that both events were chaperoned by widespread ocean anoxia or low oxygen levels. The best evidence of this phenomenon was found in the layers of black shale.
Discoveries suggest that the main form of death that rampaged throughout the Devonian era was asphyxiation.
Although it is difficult to suggest what could have caused the rapid decline of oxygen levels in the ocean, volcanic activity is often a suspect of extinction investigations. Algeo says that searchers for other plausible candidates are on their way. Despite no clear evidence being found, researchers suspect that a large igneous province, Vily Traps, could have played a key role in the mass extinction, even including mercury poisoning.
At the same time, an asteroid struck the Earth, leaving a 40-mile-wide Siljan crater.
A recent study concludes that ultraviolet radiation was the prime trigger for the Hangenberg event penetrating the atmosphere via a tear in the ozone layer.
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