Researchers find the reason behind mass extinction on Earth 420 million years ago

Around 420 million years back in the pre-historic Silurian Period, Earth suffered a major mass extinction, which wiped out almost 23 percent of the marine life. However, the reason behind this major mass extinction of Earth, which always remained a mystery, has now been unravelled by researchers. They have found an answer to this event considered as one of the ten most dramatic extinctions in Earth’s history. Referred to by scientists as the Lau/Kozlowskii extinction, it was triggered by an all-too-familiar culprit: rapid and widespread depletion of oxygen in the global oceans. The findings of the study were published in the journal — Geology and the study was conducted by researchers from Florida State University. [caption id=“attachment_7266871” align=“alignnone” width=“1280”]  Representational Image.[/caption] Unlike other famous mass extinctions that can be tidily linked to discrete, apocalyptic calamities like meteor impacts or volcanic eruptions, there was no known, spectacularly destructive event responsible for the Lau/Kozlowskii extinction. “This makes it one of the few extinction events that is comparable to the large-scale declines in biodiversity currently happening today, and a valuable window into future climate scenarios,” said study co-author Seth Young, an assistant professor in the Department of Earth, Ocean and Atmospheric Science. Scientists have long been aware of the Lau/Kozlowskii extinction as well as a related disruption in Earth’s carbon cycle during, which the burial of enormous amount of organic matter caused significant climate and environmental changes. But the link and timing between these two associated events – the extinction preceded the carbon cycle disruption by more than a hundred thousand years – remained stubbornly opaque. “It has never been clearly understood how this timing of events could be linked to a climate perturbation, or whether there was direct evidence linking widespread low-oxygen conditions to the extinction,” said Chelsie Bowman, FSU doctoral student, who led the study. Researchers used advanced geochemical methods including thallium isotope, manganese concentration, and sulfur isotope measurements from important sites in Latvia and Sweden to reconstruct a timeline of ocean deoxygenation with relation to the Lau/Kozlowskii extinction and subsequent changes to the global carbon cycle. The team’s new and surprising findings confirmed their original hypothesis that the extinction record might be driven by a decline of ocean oxygenation. Their multiproxy measurements established a clear connection between the steady creep of deoxygenated waters and the step-wise nature of the extinction event — its start in communities of deep-water organisms and eventual spread to shallow-water organisms.