The Earth has experienced five major extinction events in its history. Although there have been many smaller incidents, these five represent the most catastrophic. Of all the species that have lived, 99% are now extinct. These events have helped pave the way for human conquest of the planet, but also serve as a warning.
The first known major event occurred around 450 million years ago. During this period, all life existed in the oceans. A sharp decrease in carbon dioxide and rise of oxygen in the atmosphere appears to have weakened the planet’s ecosystems. Then, an ice age struck, cooled the planet, and glaciers lowered sea levels destroying various niches. Over 60% of species perished. Eventually, the Earth warmed and sea levels increased marking the end of the Ordovician-Silurian event.
About 100 million years later, the Late Devonian extinction began and lasted 20 million years. Some believe an asteroid triggered the event. There is evidence of oxygen depletion in the oceans. This could represent an impact or severe climate change from volcanic activity. The event seems to have only affected marine life. Scientists estimate that 75% of marine life, mostly invertebrates, went extinct.
The Late Devonian event centered on the oceans while the Permian-Triassic extinction affected so many species, scientists dubbed it “the great dying.” 96% of marine life, 70% of terrestrial animals, and many insect species went extinct. It decimated life on Earth, which took a very long time to recover. No one is sure what caused the mass extinction. Suspects range from asteroid impact to volcanism to lowering sea levels. As a result, the world changed dramatically allowing for the rise of dinosaurs and the retardation of mammalian evolution.
Mass extinction opened the evolutionary door for the dinosaurs. The reptiles survived the Permian event and the end of the Triassic marked another extinction. Around 200 million years ago, at least half of all species died out. The dinosaurs moved into the vacuum and emerged as the planet’s dominant species. The best evidence points to mass volcanic eruptions.
While two mass extinctions benefited the dinosaurs, the K-T event wiped them out. About 75% of all species became extinct including all large animals. Geologic evidence points to an asteroid impact. The resulting impact created a firestorm and mass tsunamis. Only small creatures capable of hiding and riding out the apocalypse survived to evolve into humans. After the extinction 65 million years ago, birds and mammals emerged to fill the old niches.
Lesser events augmented the five major extinction events. In fact, the world has been undergoing an event for the last 50,000 years. Some believe mankind responsible for a great number of extinctions. It is clear that humans are responsible for the dodo bird and other species, but most of the extinctions are probably natural. Since 99% of all species no longer walk the planet, humans could also go extinct.
The world has experienced many extinction events. In fact, 99% of all species no longer walk the planet. They either evolved, naturally selected out of existence, or could not survive an extinction event. The five events should serve as a warning. Despite human technology, a cosmic or mass volcanic event could easily destroy Homo sapiens as easily as the dinosaurs.