1 — Meteorite Impact
According to Donald Yeomans, director of the Office of Program of Near-Earth Objects, NASA, the risk of dying as a result of the impact of the near-Earth object is roughly equivalent to the risk of dying in a plane crash. To cause a big problem to our civilization, the impact would have to be about 1.5 kilometers wide or greater. We expect an event of this type roughly in a million years. The dangers associated with this big impact include a huge amount of dust in the atmosphere that could turn the sunlight off for weeks affecting plant life and crops. Storms and forest fires would result in the re-entry of hot fragments and severe acid rain on Earth. Although the possibility of such an incident is quite low, it cannot be neglected completely.