ABSTRACT
Evidence suggests that life on Earth has existed for about 3.7 billion years. As far as we know, life is unique to our planet. Why is this so? What is life? There is no absolute reason why we should be able to answer these questions, but we are an inquisitive species and like to get to the bottom of things. Scientists have looked at living things in a systematic way and have provided some answers to these big questions. For example, we now know what living things have in common and what conditions are essential to support life. This chapter looks at life on Earth from the chemicals needed to build living things to the great diversity of life forms that colonise almost any habitat available on the planet.
