Asteroids, pandemics and natural disasters. All have the potential to alter the course of life on Earth - and so do solar flares.
The flares - or geomagnetic storms - can cause interferences with radio waves, as well as some power outages and a blasted out from the surface of the sun with the equivalent force of up to 2.5 million nuclear bombs.
They are also responsible for the Northern Lights, which were seen as far south as northern England last week when a moderate storm.
Solar flares are measured on a scale of one to five established by the US National Oceanic and Atmospheric Administration's (NOAA). Five is the strongest and is known as a 'G5' storm. These only occur around four times every 11 years, which is the approximate length of one solar cycle.
Last week's storm was a G2 storm.
The equivalent of G5 storm has hit the Earth since was the Carrington Event in 1859. Telephone lines were set on fire and the northern lights were seen in the Caribbean.
But we now have a society that is far more reliant on technology, so what would happen if a huge solar flare hit now?
What would happen if a huge solar flare hit?
The possibility of a G5 solar flare hitting is very low, but the predicted events make for grim reading.
NOAA said: "Widespread voltage control problems and protective system problems can occur, some grid systems may experience complete collapse or blackouts.
"Pipeline currents can reach hundreds of amps, high frequency radio [use] may be impossible in many areas for one to two days, satellite navigation may be degraded for days [and] low-frequency radio navigation can be out for hours.
They also argue that the Northern Lights could be seen as low as Spain or north Africa.
The damage to the economy would be huge. Transportation that relies on GPS, such as aeroplanes, would struggle and internet access would likely experience blackouts for some time.
Repairing power grid would be time consuming and costly.
Current estimates indicate that several billion pounds a day would be lost.
What is a solar flare?
NASA explains that gases in the sun are constantly moving - this generates a great deal of what is known as 'solar activity'.
The level of activity changes depending on the point in the solar cycle, which lasts around 11 years.
NASA explains: "The magnetic field lines near sunspots often tangle, cross, and reorganise. This can cause a sudden explosion of energy called a solar flare. Solar flares release a lot of radiation into space.
