Comets, asteroids, and meteors

Earth has periodically been hit by asteroids, comets, and other space debris large enough to abruptly change the climate. The best-known event was the Cretaceous–Paleogene (K–Pg) extinction event ~65 million years ago when an asteroid impact blew dust, soil, and rocks not only into the atmosphere but also out into space, where it fell back into the upper atmosphere, creating a dust shroud for weeks to months. This blocked out sunlight which led to a cool ‘impact winter’ for years.

Worse, the asteroid slammed into rocks rich in carbonates, that is, they were full of carbon. This along with global-scale wildfires that also released huge quantities of CO₂ into the atmosphere from incinerating everything led to a rapid global warming of ~5°C following a relatively brief ‘impact winter’ cooling period. Evidence of the impact can be seen in a layer of iridium dust from the comet, in the Waipara River, North Canterbury (Fig. 1).

• There is evidence that large scale volcanic eruptions in Northern India may have contributed to this warming.
• Dust from an extraterrestrial impact event near (but not into) Earth ~466 million years has been implicated in an an ‘impact winter’ that led to an Ice Age.
• The Eocene–Oligocene extinction event 35 million years ago may have been triggered in part by up to five impact events including Popigai, Siberia and Chesapeake Bay, US.