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What environmental effects can follow a very large asteroid or comet impact on Earth?

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four impact craters — Meteorite crater Four impact craters of the same size (30 km [20 miles] in diameter) imaged by spacecraft on different solid bodies of the solar system and reproduced at the same scale. They are (clockwise from upper left) Golubkhina crater on Venus, Kepler crater on the Moon, an unnamed crater on Jupiter's moon Ganymede, and an unnamed crater on Mars. The images are oriented such that the craters appear illuminated from the left; the Venusian crater is imaged in radar wavelengths, the others in visible light.

A very large asteroid or comet impact on Earth can cause catastrophic environmental consequences that threaten global life. The immediate effects of such a collision include tremendous devastation, powerful earthquakes, widespread wildfires, and giant sea waves known as tsunamis.123

Beyond the immediate physical destruction, these impacts can significantly alter the global environment by ejecting massive quantities of fine dust, debris, and sulfur into the atmosphere. This global cloud can block sunlight for years or even decades, leading to a prolonged period of darkness and a dramatic drop in surface temperatures, often referred to as an "impact winter".143

The resulting lack of sunlight halts photosynthesis, causing the collapse of plant life and the disruption of the food chain, which can lead to worldwide starvation and mass extinction. Additionally, the vaporization of sulfur-rich minerals can create sulfuric acid in the atmosphere, potentially resulting in acid rain that acidifies and alters the chemical composition of the oceans. Such events are believed to have triggered major mass extinctions in Earth's history, including the event that ended the Cretaceous Period.1243