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Whatsapp Archean stromatolites are the first direct fossil traces of life on Earth. These are at Lake Thetis in WA.

After being pelted with meteorites for half-a-billion years, life began to appear on Earth. The miraculous leap happened around four billion years ago, when the atmosphere was blanketed with lethal gases and the ocean was thick with iron. Wendy Zukerman examines how life formed in these conditions and why it didn’t appear anywhere else nearby.

Despite phenomenal advances in modern science, the fundamental question of why life started on this planet remains unanswered. Over the past century, however, scientists have slowly been piecing together the story of our very first ancestors.

They have been cooking with chemicals they believe the early Earth was swimming in and they are forging the molecules which, over billions of years, are thought to have evolved to become, well, you and me. There is still much to understand, however.

Our hypothesis is that building blocks of RNA, which are relatively complicated organic molecules, could self-assemble.

‘There are huge difficulties in looking back to see exactly how life did get established,’ says Matthew Powner, a professor of chemistry at University College London. ‘The rock record runs out before life was established.’

For life to have begun, something that could encode information and replicate itself was necessary. A molecule—or perhaps a group of molecules—would have done the trick. Once these substances could replicate themselves, it’s believed that natural selection would have stepped in to create new versions of the ‘Great Starter’.

‘Slight errors in that replication give rise to slight variations on the theme,’ says Powner. ‘That can give them an evolutionary advantage which can then be potentially passed on more readily, and then you have, effectively, an evolutionary arms race.’

These Generation 2.0 molecules, for example, would be better equipped to multiply and survive than their predecessors. What was that first ingredient that kicked off life on Earth, though?

DNA might seem to be a likely candidate—after all, it’s the genetic material that makes us who we are. Unfortunately, however, DNA is not self-sufficient. It needs proteins to replicate. These proteins act as enzymes that speed up chemical reactions. However, it’s thought that such catalytic helpers did not exist in the early days of our universe.

In the 1960s, scientists exploring the beginnings of life started turning their attention towards another molecule: RNA. These days, RNA is thought of as a middleman that helps its more famous cousin, DNA, complete its jobs. Fifty years ago, however, evidence emerged that once upon a time this molecule was more than just a courier. Scientists found that RNA could bend itself in similar ways to a protein—suggesting that, just possibly, RNA once acted as a self-replicating entity as well as its helper protein.

It was an interesting idea, but it would take around two decades before evidence was found that the RNA molecule didn’t just bend like a protein, but could act like an enzyme. The discovery was made in the 1980s by Thomas Cech, now a professor at the University of Colorado in Boulder. He later won a Nobel Prize in chemistry for the finding. There was a clear leader in the game of ‘what molecule birthed the origin of life’.

‘Our hypothesis is that building blocks of RNA, which are relatively complicated organic molecules, could self-assemble,’ says Powner.

The case is far from settled, however. Intriguingly, RNA can’t self-assemble anymore. Like DNA, both molecules need to be stitched together using other enzymes. As a result, scientists cannot be sure that RNA was ever self-sufficient enough to copy itself in a hostile primordial world, though new evidence has come to light that it may not have needed to. The toxic environmental conditions of the day might have given the molecule a helping hand.

Last year, Markus Keller and his colleagues at Cambridge cooked up samples of the type of water that would have filled our oceans around four billion years ago. The team heated the potion up to 70 degrees, mimicking the scalding temperatures thought to have emanated from hydrothermal vents.

They found evidence that some of RNA’s parts could have been forged in that fury. Just last month, a different group from Cambridge found that two compounds—hydrogen cyanide and hydrogen sulphide—which would have flourished in an infantile Earth, could also trigger the production of RNA’s building blocks.

This leads to the question: where did life originally form? Was it in those fiery vents? Nick Lane, an evolutionary biochemist at University College in London, believes so.

According to Lane, the environment that created life would need to be ‘continuously’ producing the building blocks of RNA in ‘large numbers’. ‘Any form of replication is doubling,’ says Lane. ‘So you need an environment that will feed you.’

‘This is one of the problems with a soup,’ says Lane, referring to Darwin’s 1871 theory that life emerged in a ‘warm little pond’—a soup of chemicals showered in light and heat. ‘You simply run out of ingredients very, very quickly—the concentration is too low.’

Matthew Powner isn’t giving up on Darwin’s soup just yet, though.

‘We are thinking about a scenario where you have pools or shallow bodies of water,’ he says.

According to Powner, placing the origins of life in the depths of the ocean would lose a key piece needed in the creation of RNA: UV light. ‘Ultraviolet light provides an energy source for certain chemical reactions to take place,’ he says. ‘The importance of ultraviolet light suggests that the chemistry would have taken place near the surface of a body.’

So the debate rages on. Over the past few decades scientists have edged closer to understanding the origin of life, but there is still some way to go, which is probably why when Robyn Williams asked Lane, ‘What was there in the beginning, do you think?’, the scientist replied wryly: ‘Ah, “think”. Yes, we have no idea, is the bottom line.’

Investigating the origins of RNA and life Listen to this episode of The Science Show to hear about the work scientists are doing to discover the origins of our planet.

The Science Show gives Australians unique insights into the latest scientific research and debate, from the physics of cricket to prime ministerial biorhythms.

