THE RECIPE FOR LIFE 1) Take the ingredients for life and mix together to make a primordial soup 2) Add energy 3) The ingredients will react together, forming a variety of complex molecules 4) Wait for these molecules to reproduce themselves and life has begun

What is primordial soup? Artist's Impression of the early Earth The seas of the early Earth are often referred to as the 'primordial soup'. They contained a cocktail of simple chemicals, with all the ingredients for life.

To find out if there is life in the Universe, it's useful to look at how it began here on Earth. Follow our step-by-step recipe to see how life started.

1) Mix ingredients

For life to evolve, simple molecules have to combine to form more complex ones. This mixing would have happened in the seas of the early Earth, often called the 'primordial soup'.

2) Add energy

Next you need energy. This may have come from lightning storms or hot underwater springs. This injection of energy sparked chemical reactions. These simple molecules began joining to form larger, more complex ones, called 'amino acids'.

In a classic experiment in 1953, Stanley Miller and Harold Urey recreated the primordial soup in the laboratory. By passing electricity through a mixture of simple molecules, they were able to make amino acids.

3) Form complex molecules

Amino acids then joined together end-to-end to form long, chain-like molecules, known as proteins. Proteins are essential for building a living creature. They are involved in the formation of just about everything in your body, from the colour of your skin to the layout of neurons in your brain.

4) Wait for life to reproduce

Another complex molecule that was formed during these reactions was DNA. DNA has an amazing characteristic that makes it essential for life - it can reproduce itself. It also carries all the code to make a living creature.

Is this one of the oldest fossils yet found?

The earliest fossils

Over millions of years, this concoction of molecules evolved into bacteria. The earliest fossils we have found on Earth are simple, single celled bacteria about 3.8 billion years old. These are the ancient ancestors of all life on planet Earth today.

Did life arrive from space?

But not all scientists agree that life evolved from chemicals in the primordial soup. Some think the seeds of life may have come from space on a comet.