Abel Straker, of Westland High School, asks :-

Toby, of Balclutha Primary School, asked:-

How long would life continue if the sun stopped shining? Would we/could we live without light?

John Walker, a biochemist in the Plant and Microbial Sciences Department of the University of Canterbury, responded.

If the sun were to be suddenly and totally extinguished then life as we know it on this planet would cease very rapidly. I would guess at times as short as one to four weeks.

If it were a slower loss of solar radiation then events would be more gradual and ultimately would depend on the rate of disappearance of plant life.

What I would expect to happen would be something like this. With a slow change the earth would gradually get colder so that plants and animals in temperate climates would either die or migrate towards the equator. The rates of consumption of fossil fuels by humans would increase dramatically with a resulting increase in carbon dioxide in the atmosphere. However life would still continue for a long time.

Near total loss of sunlight would result in the death of all green plants. This would have disastrous consequences in several ways because plants, in absorbing the light from the sun, produce sugars and hence the food supply for animals and humans. No sun, no food. We would starve!

However, before we died of starvation, we would probably die from lack of oxygen and/or carbon dioxide poisoning since it is only the process of photosynthesis by green plants that takes in carbon dioxide (one of our waste products) and emits the oxygen we need.

Despite the above gloomy outlook not all living things would perish. Many micro-organisms could continue to live on dead and decaying matter. There are whole communities of bacteria and small animals like crabs and marine worms that live in complete darkness around warm volcanic vents in the deepest parts of the oceans and I guess that they would be little affected by loss of sunlight and could continue to survive until the inner reaches of the earth finally cooled down.

There is an interesting science fiction book, written by Fred Hoyle and called "The Black Cloud" which deals with the events when an inter-galactic cloud arrives and almost blots out our sun.