The Elements of Evolution (4-4) Extinction Events continued


The worst extinction event of all time was 252–248 MYA, at the end of the Permian. The Paleozoic era closed with  an extinction event that drove life’s diversity on land down to 5 to 10% of what it had been. At least 90% of terrestrial species and over 50% of marine families were wiped out during the Great Dying.

The multiple-pulse Triassic–Jurassic extinction event 217–199 MYA profoundly affected life on land and in the oceans. Most large amphibian species vanished. 20% of all marine families went extinct. Plant biodiversity was not severely affected, as plants adapted, though there was considerable species turnover in the mix of vegetation.

Global warming had an impact but does not explain the sudden demise of marine life during the Triassic–Jurassic mass extinction. No massive meteorite craters that can be considered causal have been found. Some evidence indicates voluminous volcanic eruptions at the time, though conclusions to causes are still speculative.

The last great extinction event, at the Cretaceous–Paleogene (K–Pg) boundary, 66 MYA, set the stage for the large life forms found today. There was an 80% elimination in marine invertebrates, a drastic drop in mammal species, and the utter demise of dinosaurs, save the birds that soar to this day. All told, 60–80% of all animal species were snuffed. The only marsupial to make it were opossums. Plants were profoundly affected by the abrupt changes caused by a bodacious bolide bashing into the Yucatán peninsula.

There have been numerous minor extinction events: minor only by comparison to those that were devastating. The disruptions to life in the lesser extinction pulses were dramatic, though not nearly as drastic as the vast numbers lost in major events. As an example: 183 MYA, a relatively minor mass extinction – the Early Toarcian oceanic anoxic event – wiped out more than 80% of the marine bivalve species, such as clams. Many shallow-water species went extinct. Oceanic methane release from tectonic plate movement was the probable cause.