Scientists make chemical hallmarks of life with lasers

Using a laser to simulate asteroid and comet impacts on the early Earth, scientists have created the chemical building blocks of DNA in a dish...

How life began on Earth about 4 billion years ago remains one of science's great unsolved mysteries. One theory is that families of chemicals appeared that developed the ability to replicate themselves. Over time they evolved to surround themselves with a fatty bubble forming the first cells and, ultimately, evolved over billions of years to become complex life, like us.

But did the critical chemicals that kick-started life on Earth arrive from space, or were they generated here? Now scientists in the Czech Republic have contributed an important piece to the puzzle by showing that it's possible to create all four of the genetic "letters" found in DNA in a simulated comet or asteroid strike.

Around 3.9 billion years ago the Earth was subject to an intense 150 million year battering called the Late Heavy Bombardment during which up to one billion tonnes of material per year slammed into the planet from space at speeds of up to 20 kilometres per second, creating huge, explosive and high-energy impacts.

Writing in PNAS, Czech Academy of Sciences researcher Martin Ferus and his colleagues recreated these conditions using blasts from a powerful iodine laser to zap solutions of clay and a simple chemical called formamide. This contains carbon, hydrogen, nitrogen and oyxgen and was thought to have been common on the early Earth.

The brief strikes from the laser, each lasting less than one third of one billionth of a second, were similar in energy density to the punch packed by an impacting comet or asteroid. This heated the samples to over 4000 degrees Celsius, producing UV and X-rays and also creating powerful shockwaves in the materials as they expanded. This produced a flurry of chemical reactions as molecules were sequentially ripped apart and then recombined in new ways.

Incredibly, the result was a mixture that included three of the four genetic letters found in DNA and all four of the genetic letters found in its chemically simpler cousin, RNA, which is thought to be the first form of genetic material to have existed on Earth.

Critics of the work have pointed out that the molecules were produced only in very low abundances, and that there being sufficient formamide available on the Earth at the time might be a tall - but not impossible - order.

Either way, the work offers new insights into how some of the most important molecules that underpin life might have come into being.