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If given a time machine, almost every biologist on Earth would race to be sent back to the same place, at the same time.

An inconspicuous-looking shallow rock pool, 4.28 billion years ago.

They’re there to witness the most important thing to ever happen on Earth. Abiogenesis.

It’s an event that left no direct evidence. It created something so small, and so fragile, that it never left a trace. However, we carry its imprint within every cell of our bodies.

Abiogenesis happened when one molecule learned how to make a copy of itself.

Chemistry can pull off some pretty surprising things but this one was truly special. It crossed a threshold and became life. Or at least took the most crucial step towards it.

Scientists dispute how exactly abiogenesis happened, making it one of the most fundamental and important mysteries in science, but we do have some ideas about the big picture.

First, a bit of context.

The Earth is unique among all the planets in our solar system as it is an oasis for complex chemistry.

Water engulfs the entire planet, stirring up its minerals and giving them a place to mix and combine, while the sun heats them but without being so hot that they break apart. There is an abundance of carbon dioxide, methane, and ammonia, chemicals that can combine into billions of variations.

One place where this complexity really comes together is in coastal rock pools, just like the ones we have today. They are an ‘interface’ between the gasses in the atmosphere, the minerals in rocks, and water and the substances dissolved within it. After millions of years of being stirred by heat from the Sun and being zapped by occasional bouts of lightning, an inundation of strange and wonderful molecules formed in these pools.

Scientists call this the ‘Primordial soup’.

Rock pools may be life’s original environment. Look at them now! Video by Mark Gee.

In the soup, it is believed that our exceptionally interesting molecule formed.

It was some unique combination of smaller molecules, called base pairs (or maybe parts of base pairs. We don’t know), each of which floated freely and abundantly in this primeval soup. Something like 165 of them happened to join up, by chance, in just the right way.

That was the moment that changed the Earth forever.

By combining in this way the base pairs gave the molecule a special attribute.

The molecule could attract similar base pairs from the surrounding water, hold them in place, and most importantly join them together. It was like a template, or a mold, that easily and naturally combined base pairs.

In doing so it made copies of itself out of the surrounding soup. In other words, it created a second generation.

We don’t know the exact chemical nature of this original ‘replicator’ like what base pairs it had, or how long it ‘lived’ for. After 4 billion years it has left no fossils, and nowadays all base pairs that might show up in a rock pool are eaten by bacteria.

What we do know is the second generation of copies inherited the ability to replicate. They made their own copies, which made their own copies. Before long, the replicating molecules proliferated and spread throughout the sea wherever the environment allowed and base pairs were available.

The replicators are called RNA, an ancestor to the DNA that we now carry in every cell in our bodies. This period in time is called the ‘RNA world’.

Eventually, later generations discovered how to build walls around themselves to protect the vulnerable RNA, and even how to eat molecules from the surrounding water and use their energy to move around.

Generation after generation they became more complex, building elaborate structures around themselves. Some learned to capture energy from sunlight and became the ancestors of all plants. Others learned to consume other cells and became the ancestors of all animals.

Eventually, RNA was replaced by its descendant called DNA. All of life today, from towering Redwood trees to the human being, carries this descendant DNA in every one of our cells. We are all variations of these fundamental molecules and the bodies they constructed around themselves that were the catalyst of an explosion of complexity and beauty greater than any other we have observed in the known universe.

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Ben McCarthy

Ben McCarthy

Ben is the Founder of Discover Earth and the author of the Big Ideas Network.