'90% of life on Earth died out 250 million years ago.'
The event scientists have dubbed "The Great Dying" marked the end of the Paleozoic era. Throughout this era, the continents were combining in the supercontinent Pangaea, and pre-dinosaur and pre-mammalian reptiles roamed the Earth. Suddenly, though, nearly all of the planet's marine species (around 95%) died out, likely due to environmental factors, which also coincided with the only known mass extinction of insects. Several theories have been proposed as catalysts (an impact event, volcanic eruptions), but regardless, the end result was the largest extinction event on record.