A key part of the puzzle to work out how life emerged on Earth may have been found after British scientists identified a crucial ingredient that was present four billion years ago.

Their research suggests that the first living organisms may have developed in lakes or other fresh water.

This would overturn the view that the first cells must have emerged in small pools that could periodically dry out, such as those formed by volcanic hot springs, which regularly dry up in the sun before being refilled.

For decades chemists and biologists have been conducting experiments to try to solve one of the biggest riddles in science: how did all of the characteristics that make up living organisms, from structured cells and RNA (which stores templates for protein production) to the ability to replicate and absorb energy, come together to make the earliest micro-organisms? A molecule that is essential to all living things on the planet today was thought to have been absent when the earliest cells formed because the conditions were not suitable for it to form.

Scientists have now managed to create the compound in a laboratory experiment that mimicked the conditions found on Earth at about the time life first emerged.

The compound, pantetheine, could therefore have played a key role in the reactions that led the first simple molecules — which acted as forerunners to proteins and RNA — to develop into the first living organisms, scientists from University College London (UCL) said.

In modern organisms, pantetheine is important for metabolism, the energyharnessing process in all living things.

In 1995 Stanley Miller, the American chemist who devised some of the earliest experiments in search of the origins of life, tried to create pantetheine in a laboratory to test whether it could have existed on Earth four billion years ago.

He was able to create only tiny amounts, by using very high concentrations of chemicals that were heated to 100C. Scientists therefore concluded that it could not have existed on the early Earth.

UCL researchers, however, used a method that employed hydrogen cyanide, which was thought to have been abundant on the early Earth. They created the pantetheine using aminonitriles, energy-rich molecules that are related to the amino acids that act as building blocks for all life.

They were able to create pantetheine in water at room temperature, showing that it could be created in conditions that were possible on early Earth.

Dr Saidul Islam, a lead author of the study published in the journal Science, said: “Because pantetheine looks so unusual and complex, it has always been thought that its creation must have come after the advent of complex life. But our work suggests this molecule has always been there, and if so, it certainly would have contributed to the beginning of life on this planet.”

Paradoxically, although water is essential to all living things, it can be destructive to the core components needed for life because water can break down the links that hold proteins, DNA and RNA together.

Scientists disagree over whether life could have emerged in water or if it would have needed dry periods for the key ingredients to come together without being destroyed. The concentration of chemicals would have been too dilute in the ocean for the reaction to have occurred there, researchers said.