The major elemental abundance differences between life, the oceans and the Sun

As we begin to understand the origin and evolution of life on Earth and investigate the possibility of extraterrestrial life, the need to scientifically approach fundamental questions such as ‘What is Life ?’ increases. In beginning to answer such questions we can look at the ingredients of life on Earth. Here we present an overview of our understanding of the composition of life on Earth. At the level of chemical elements, the major ingredients are carbon, hydrogen, oxygen, nitrogen, sulphur and phosphorus along with trace amounts of elements like sodium, potassium, iron and copper. Here we present the correlation between the elemental composition of life (humans and bacteria), the Sun and sea water. Some elements like carbon, nitrogen and phosphorus are more abundant in life than in sea water, while others like chlorine and sodium are more abundant in sea water than in life. We quantify differences in elemental abundances in life, relative to sea water and attempt to interpret them in terms of chemical constraints on metabolic activities and harnessing energy. We discuss how future investigations could further our understanding of the origins and evolution of life on Earth. While natural philosophers1 believed all matter to be made of four elements: fire, air, water and earth, we now recognise that all matter in the universe is made of atoms of chemical elements.2 The first chapter of De Courcey’s 1857 book [1] is titled: “A chemical analysis of the elements which are found to exist in the human frame thus showing the natural origin of man.” It is perhaps one of the earliest records where one has examined the composition of life in terms of chemical elements. De Courcey mentions that vegetable and animal matter are essentially composed of carbon, hydrogen, oxygen and nitrogen in addition to sulphur, phosphorus, iron and small quantities of “saline matter” (for example sodium and