Elements of life

As far as we know, there are very few planets in the universe which are just like our planet Earth. The elements it is made from have played a critical role in allowing life to exist here. However, there may be planets out there whose composition is very different. There is a huge range of possibilities – perhaps there is no oxygen, only sulfur or very little phosphorus but a lot of arsenic. Could life exist on such planets? Scientists have thought about this question for decades. To answer it, we need to understand more about DNA, the molecule of life, the elements it is composed of and consider the results of some unusual experiments.