Another potential threat to the Earth is the impact of a large asteroid or comet. While the chances of a catastrophic collision are relatively low, such an event could have devastating consequences for life on the planet. An asteroid impact could trigger massive fires, tsunamis, and a "nuclear winter" effect that would block out sunlight and plummet the Earth into darkness and cold. On a longer timescale, the Sun will eventually run out of fuel and expand into a red giant, swallowing up the inner planets, including Earth. This process, known as stellar evolution, is estimated to occur in about 5 billion years.
