Greetings. There have been several major extinction events during the long history of the Earth. Asteroid impacts have been the primary cause of at least one, the Cretaceous/Paleogene extinction event, which took place 66.043 million years ago.
The situation is likely a universal one, with life forms across the galaxy(ies) at the mercy of random occurrences, impact events which are devastating to natural habitats and environments. Here on the Earth, life forms have arisen and gone extinct, some due to gradual environmental processes, many due to catastrophic extinction events, which end up challenging the planet's ecosystems and their ability to recover from the brink. The human species is no different, for we are involved in that very same play. We often think of our species as the summit of the planet's evolutionary processes, the rulers of the Earth. However, our mere presence has absolutely nothing to do with the grey matter contained within our skulls, it has everything to do with events beyond our control. Impact events.
Early on in the solar system's history, impacts were far more commonplace, with the space between the newly formed planets full of dust and debris left over from the system's initial formation. Scattered amongst that debris were innumerable rocks, asteroids, and planetesimals, some minute in size, some far more substantial, far more potentially destructive. The Earth experienced many impact events in its very early history, but as the planetary environment began to slowly quiet down, such events became less and less common. The historical record of the Earth's impact events has mostly been covered up, due to various natural processes; continental drift, climate changes, weather erosion, and volcanism, among others. On the other hand, many of Earth's planetary neighbors, Mars, Mercury, and Pluto, have multiple impact scars prominently displayed on their battered surfaces, mostly due to the absence of the very same natural processes active on the Earth.
As life arose on the Earth, it became an unwitting target for destruction, via such random impact events. Life has evolved, advanced, and diversified, and will continue to do so until the Sun burns through its fuel source and destroys the Earth. Peppered between times of advancement and diversification, extinction events have destroyed life forms, leaving ecological niches behind, wide open for opportunists to fill. Life is killed off, and rebounds, is killed off again, and again, rebounds. This evolutionary play has been going on since life first appeared a few hundred million years after the Earth cooled off after its formation. Now human beings have appeared on the scene, a technologically capable species of bipedal hominid.
We think of ourselves as invincible, the end all be all of evolution, but we are not. We simply have had enough time to evolve, advance, and diversify to attain a level of intelligence and technological capability. A random impact event would bring that all to an abrupt close, especially if the incoming body was comparable to the Cretaceous/Paleogene impactor, which was approximately 15 kilometers, or about 9 miles in overall size. Our technology would not do us any good against such a rocky projectile. Our intelligence has gotten us to a certain point, which is a credit to our species, but random chance has played a part in our evolutionary journey too. If an asteroid impact had occurred during the Pliocene or the Pleistocene, our species may have been extinguished. No wars. No Hitler. No Einstein. No Kennedy. No Eisenhower. No moon landings. No Pearl Harbor. No Golden Gate Bridge. No United States of America, or any other sovereign country. Nothing but peace and quiet, and evolution.
Makes one take into account how lucky we are to have gotten this far down the evolutionary road.
Thank you for your time and consideration.
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