Life on Earth Wednesday, 26 December 2018 L.o: to know that there are many theories for how life on earth began, and to understand one such theory. Wednesday, 26 December 2018

Evolution of life There are lots of different theories to explain how life might have evolved.

Primordial soup theory The primordial soup theory states that billions of years ago, the Earth's atmosphere was rich in nitrogen, hydrogen, ammonia and methane (a hydrocarbon). Lightning struck, causing a chemical reaction between the gases, resulting in the formation of amino acids. The amino acids collected in a ‘primordial soup' — a body of water out of which life gradually crawled. The amino acids gradually combined to produce organic matter which eventually evolved into simple living organisms.

Primordial soup theory In the 1950s, Miller and Urey carried out an experiment to prove this theory. They sealed a mixture of the relevant gases in their apparatus, heated them and applied an electrical charge for a week. They found that amino acids were made, but not as many as there are on Earth. This suggests the theory could be along the right lines, but isn't quite right.

The mystery of life All the theories to explain how life began are just that — theories. We may never know for certain how or why life began. The problem is, life started about 3 billion years ago, so it's unlikely that any evidence of the earliest life forms will still be around today. We can guess, but we can't really know for sure what the conditions were like when life started and we don't yet have the capability to test a lot of the theories.