Life on earth has been plagued with mass extinctions throughout its history. Many scholars cite five, well documented mass extinctions, where between 50% and 90% of all species alive at the time died out. However, at least fifteen other large scale extinction events have been documented. The most famous such event occurred around 65 million years ago and did in the dinosaurs—as well as many other species.
Mass extinctions are due to world-wide (or nearly so) environmental catastrophes that result in drastic alterations to the global climate. An asteroid impact or wide-spread volcanic eruptions can not only directly destroy local environments, but they can throw so much dust and debris into the upper atmosphere that sunlight is greatly diminished. This can cause drastic cooling of the climate and wreck the process of photosynthesis. Once the photosynthetic plants die, everything that feeds on them dies. The carnivores are the next to go.
In 1883, the volcanic island called Krakatoa, which lies in Indonesia near Java, erupted, producing what is generally considered to be the loudest sound ever recorded in modern history. In a series of explosions, roughly two-thirds of the island disintegrated. At least a thousand people were killed immediately, and over 35,000 more died in the tidal waves that followed. (Many believe the death toll to be considerably higher.) Lower temperatures were recorded world-wide in the year after this single event, a little over 2 degrees Fahrenheit on average. It took almost five years for world weather patterns to return to normal.
Krakatoa is not actually the largest volcanic eruption in recorded history, however. First place goes to the earlier 1815 eruption of Mount Tambora, another Indonesian volcano. Over 10,000 people died from the eruption itself, and the deaths of over 70,000 are blamed on the volcano, although many died from starvation. The following year, 1816, is known historically as “the year without a summer.” World-wide effects were detected, but the British Isles and America’s New England states were among the hardest hit. Ice lingered long. Crops failed. People struggled to survive.
If such single eruption events could have this kind of impact, imagine what the simultaneous or near simultaneous eruptions of many volcanoes could do. It wouldn’t even have to be a great dramatic event. The signs of large scale and long-term volcanism are clearly seen in the geological history of earth. Several of these periods have been correlated in time with mass extinctions. For example, most of Siberia was covered with lava flows around 250 million years ago. The increased volcanic activity in Siberia at that time may have lasted nearly a million years and certainly would have had major impacts on earth’s climate, setting off a cascade of events that collectively shocked the planet’s biosphere. This great volcanic conflagration corresponds with the biggest of the known mass extinctions, the so called “Permian-Triassic event.” Almost 90% of all life on earth perished at that time.