Life brought to Earth by comets

Life on Earth may have been sparked by comets carrying with them the key ingredients for our existence, scientists claim.

The combination of water, energy and amino acids – which bind together to form proteins – could have caused the first chemical reactions which are believed to be the origin of life

NASA scientists have replicated the impact of a comet and demonstrated that amino acids, a building block of life, could have survived the intense heat and shock waves given off in the collision.

The combination of water, energy and amino acids – which bind together to form proteins – could have caused the first chemical reactions and created proteins, the researchers said.

Presenting their findings at a meeting of the American Chemical Society, they said that several comets, asteroids and meteorites arriving over a long time span could have brought repeated batches of these ingredients to the primordial Earth.

Comets, giant balls of frozen gas, ice, dust and rock which measure up to 10 miles in diameter, orbit the Sun in a belt far more distant than the furthest planets, but occasionally break free and zoom directly into our solar system.

Existing evidence suggests that life began on Earth about 3.8 billion years ago during a period known as the "late heavy bombardment", when the planet was battered by vast numbers of comets and asteroids.

Prior to that time the atmosphere on Earth is believed to have been too hot for anything to survive, and there is scant evidence of water or amino acids already being present.

To test their theory the researchers used enormous "gas guns" to fire high-pressure gas at capsules of amino acids, water and other materials at tremendously high speeds.

The amino acids were undamaged by the experiment, which mimiced the impact of a comet, and went on to form the bonds that link them together as proteins which enable life to exist.

Dr Jennifer Blank, who led the study, said: "Our research shows that the building blocks of life could have remained intact despite the tremendous shock wave and other violent conditions in a comet impact.

"Comets really would have been the ideal packages for delivering ingredients for the chemical evolution thought to have resulted in life. We like the comet delivery scenario because it includes all of the ingredients for life — amino acids, water and energy."