Extinction is the death of every member of a species. Mass extinction is the death of several species in the same time period. There have been several mass extinctions since life first evolved, but scientists have a difficult time explaining the causes because the time periods involved. From 65 million years for the last one to 450 million years for the earliest known event.
Of the seven major mass extinction events, the Ordovician-Silurian Extinction Event was the earliest and the second largest. According to the International Commission on Stratigraphy (ICS), this one occurred 440-450 million years ago. Two bursts of extinction appeared to have occurred separated by one million years. At this time, all known life was in the oceans and seas. The apparent cause appears to have been the continental drift of a significant land mass into the south-pole region, causing global temperatures to drop. Glaciation resulted in the the lowering of the sea levels worldwide. This destroyed about 80% of marine species that lived in and around the continental shelves around the world.
According to the ICS, the Late Devonian (Late D) Extinction Event was the next one that occurred 360-370 million years ago and lasted up to 15 million years. The cause is open to debate, but Michael Benton offers a theory in his 2003 book, “When Life Nearly Died: The Greatest Mass Extinctions of All Time”. He writes that the evolution of plant life could be the cause. During this time period, plants increased their size by 10,000%. Land plants expanded rapidly and used up carbon dioxide to the point where global cooling may have resulted. Plus their massive roots could have changed important things below the surface like water tables. What ever the cause, 70% of all species died.
The Permian-Triassic (P-Tr) Extinction Event, also called the Great Dying, occurred about 251 million years ago. It is the Earth’s largest extinction event. About 96% of all marine species and 75% of all land species (including plants, animals, and even insects) disappeared. This is the only known mass extinction of insects. This event was spread out over a few million years and came in two main pulses. The possible causes are supported by strong evidence and appear to describe a sequence of catastrophes, each one worse than the previous. These causes include volcanism to methanehydrate gasification to hydrogen-sulfide emissions. Or maybe a combination. But whatever the cause, it was deadly.
The Triassic-Jurassic (Tr-J) Extinction Event occurred about 205 million years ago and lasted about 10,000 years. According to the ICS, 50% of all species went extinct. But what is notable for this event is the rise of the dinosaurs. This event destroyed species that allowed the dinosaurs to assume the dominate role in the Jurassic Period for over a million years. They became the most successful species to ever walk the Earth.
The most famous and the most studied extinction event is the Cretaceous-Tertiary (K-T). It occured about 65 million years ago and killed off about 75% of all species. This one was relatively quick, lasting only a few thousand years. This event, however, is known for the death of all dinosaur species and the rise of mammals. And eventually humans. It has been an accepted theory that this event was caused by a huge single meteor hitting the Yucatan Peninsula.
But a 2004 article by L. Mullen in the Astrology Magazine, offers a slightly different theory. He claims that this extinction was caused by multiple extraterrestrial impacts around the world at about the same time. Several craters have been examined and have been determined to have occurred around 65 million years ago. These include the Chiculub Crater (110 miles in diameter) at the Yucatan Peninsula in Mexico to the Shiva Crater (370 miles in diameter) in the Indian Ocean. The Multiple-Impact Theory suggests a massive asteroid fragmenting and hitting the Earth in several locations. Whatever the reason, however, we would not be walking the Earth if not for this disaster.
The Holocene Epoch Extinction Event is occurring at this moment. Holocene Epoch is the geological time period where humans have thrived and other species have suffered or even disappeared. In a 1998 survey by the American Museum of Natural History, 70% of biologists believe we are in the middle of the fastest mass extinction in Earth’s history. It is caused by humanity’s destruction of the biosphere (the global sum of all life on Earth).
Noted scientists are debating this point. Philip Levin estimates that right now one species is going extinct every 20 minutes. Michael Bention says that there are 20-100 million species in total today. He estimates the extinction of 14-70 species a day and 5000 to 25000 a year. Bjorn Lomborg, a strong skeptic of the today’s mass-extinction theory, had written in his 2001 book, “The Skeptical Environmentalist” that the current rate of extinction is about 1500 times the natural rate. We know very little about the causes of past mass extinctions, but we certainly know the cause of our present one. It’s the destruction caused by mankind.
The Red Giant Extinction Event will occur in about five billion years, but it will be the ultimate in extinction events with an extinction rate of 100%, according to National Geographic. And we precisely know the cause. When our Sun runs out of fuel, it will gradually expand into a red giant. The Sun is too small to explode. As the red giant grows, all life on Earth will be wiped out. The red giant will eventually engulf and vaporize Earth. The ultimate mass extinction. Mankind will probably go the way of the dinosaurs long before this event, but I guess that’s for the best. Maybe Earth can become naturalized again and be happy before its ultimate destruction.