Toxic gas found in chemical weapons may have been the building blocks for life

While Earth was still being bombarded with rocks from space 4.4 billion yers ago, a toxic gas found in modern chemical weapons may have triggered the first life. 

Hydrogen cyanide, a poisonous gas that can spell death for modern-life, was one of the most important molecules in the formation of RNA, according to astrobiologists from Johns Hopkins University, in Baltimore, Maryland. 

The first life on Earth formed from these strands of RNA, which itself was made from a ‘perfect combination’ of toxic molecules combining in ‘warm little ponds’.

After the forming of RNA strands, the team suggest Darwinian Evolution took over, leading to the formation of DNA, proteins and the first simple forms of life. 

This all happened within about 200 million years of the massive collision event that led to the formation of the moon, the researchers explained.

It has remained a mystery to science whether the appearance of life on Earth happened suddenly, or was a gradual process of molecules combining to form strands complex enough to form basic life – including bacteria.

Evidence of life away from Earth has so far remained elusive, and this new study suggests it may take conditions on an entire planet to be ‘just right’ for life to begin. 

To get a molecule to replicate itself, conditions have to allow for the complex interaction of hydrogen meteorites, volcanic activity and warm ponds.

But more than this, those conditions have to then combine in such a way that they produce hydrogen cyanide, according to the team behind this new work.  

The first life on Earth formed from these strands of RNA, which itself was made from a ‘perfect combination’ of toxic molecules combining in ‘warm little ponds’

Its thought that the first simple forms of life, likely made up of strands of Ribonucleic acid (RNA), appeared between 4.5 billion and 3.7 billion years ago.

RNA is a molecule similar to DNA, but unlike DNA it is just a single strand, with a backbone made of alternating sugar and phosphate groups.

Modern life is made of a combination of DNA, RNA and proteins working in various formations and performing a range of tasks to keep us alive. 

However, a system so complex, requiring DNA to store information, RNA to transmit information and proteins to do the work, unlikely happened in one go. 

The big question, that these researchers wanted to answer, was how the first trigger, that led to the first strands of RNA, came about. 

They created a complex model of the early Earth, starting about 200 million years after the collision that created the moon – enough time for the surface to cool down.

Study lead author, Ben Pearce, started the work while at McMaster University in Canada, but is now at Johns Hopkins. 

The first oceans were starting to form around the earliest continents, but the water in the oceans was being repeatedly evaporated into the atmosphere.

It was a nasty place, with meteorites constantly battering the surface, active volcanoes covering the planet, and undersea vents leaking methane.

The meteorite impacts had a benefit, as they delivered hydrogen – an element so light it normally escapes the atmosphere unless bound up in other molecules.

As the hydrogen arrived in the atmosphere, volcanoes were sending up carbon dioxide, and oceans were evaporating as water vapor.

A combination of lightning strikes and ultraviolet radiation from the sun stirred up this chemical mixture, allowing hydrogen cyanide to be produced.

The researchers say this was likely the key moment in allowing early life to form on the planet, happening in ‘warm little ponds’ that dotted the surface. 

Hydrogen cyanide is able to react with itself, and some theories of life suggest it is a complex version of chemicals that interact with themselves. 

As well as interacting with itself, hydrogen cyanide can interact with other molecules to produce biomolecules that are the building blocks of the individual elements that make up RNA. These include nucleobases, ribose and nucleotides.

Hydrogen cyanide would rain out of the atmosphere into warm little pounds, where they would combine with other molecules, and over 100 million years the concentration would be enough to produce adenine, the team discovered. 

This is a key component of RNA and the process of ‘triggering’ the chemicals for life, such as hydrogen cyanide, only happened during the bombardment from space. 

This all happened within about 200 million years of the massive collision event that led to the formation of the moon, the researchers explained. Stock image

Over time the bombardment slowed, with meteorites no longer falling to Earth in such great numbers due to the gravity of the sun and large planets clearing their orbital path. 

At this point it is thought there was enough adenine in these warm ponds to kick start the formation of RNA strands, which then over time began to replicate and begin the first stages of life on Earth. 

‘The astrophysical and chemical processes we model are quite general,’ the study authors wrote in their pre-print paper.

‘They are intrinsic to the late phases of terrestrial planet formation, anywhere. This suggests that life on Earth, and perhaps also on other Earth-like worlds, began in the chaotic conditions that prevailed soon after their formation.’ 

The study was published in the preprint journal arXiv.