Impact events are caused by the collision of large meteoroids, asteroids or comets (generically: bolides) with Earth and may sometimes be followed by mass extinctions of life. For discussion of impacts in general, not just on Earth, see impact crater.
In the past, the Biblical view of history held that the Earth was created a few thousand years ago, and had been shaped since that time by a number of global cataclysms (see catastrophism). In the course of the first half of the 19th century, the new sciences of geology and paleontology supplanted this view, which gradually gave way to a consensus that the Earth was ancient and that its features reflected gradual changes operating over very long periods of time—a view known as uniformitarianism.
This view has been amended in recent decades to accommodate the fact that the Earth has in fact also gone through periods of abrupt and catastrophic change, some due to the impact of large asteroids and comets on the planet. A few of these impacts may have caused massive climate change and the extinction of large numbers of plant and animal species. The creation of the Moon is widely attributed to a huge impact early in Earth's history. Impact events even earlier in Earth's history have been credited with creative as well as destructive events; it has been proposed that the water in the Earth's oceans was delivered by impacting comets, and some have suggested that the origins of life may have been influenced by impacting objects bringing organic chemicals to the Earth's surface, a theory known as panspermia
