Scientists have come up with a new theory suggesting that key chemical reactions may hold the answer to the origin of life on Earth and that life’s ingredients were likely present as early as four billion years ago.

Regarding the question of when and how life first began on Earth, the only thing we are really sure of is that we are not really sure of anything.

In a recent article, we reported that scientists have traced the origin of terrestrial life back to 3.5 billion years ago with the discovery of the oldest biological microfossils ever found.

It is now likely that rudimentary forms of life may have already been present on Earth some 3.5 billion years ago while the planet was still experiencing heavy bombardment by comets and asteroids.

The microfossils discovered in Australia are considered to be the oldest evidence of micro-organisms to have lived on our planet. This fact also raises the point that if microbial life could spark 3.5 billion years ago then life had to have started much earlier than that.

But that’s only a minor part of the puzzle.

New theory suggests a chemical recipe for how life first began on Earth.Click To Tweet

The Citric Acid Cycle’s Link to Life

If the birth date of life on Earth has been pushed back once more, it raises another mystery, perhaps more challenging, on how this life first appeared.

Now, a team of chemists at the Scripps Research Institute (TSRI), are trying to answer the question of how life began with a new theory.

The theory proposes to bring a new understanding of how life could have appeared on Earth 4 billion years ago when the elements necessary for life would have been very likely available.

“This was a black box for us,” said TSRI’s Ramanarayanan Krishnamurthy, senior author of the study. “But if you focus on the chemistry, the questions of origins of life become less daunting.”

According to TSRI chemists, inert chemical compounds that were present on Earth 4 billion years ago could have chemically reacted with each other to produce the precursors of life, or what is called prebiotic elements.

The team focused on the citric acid cycle, also known as the Krebs Cycle, a series of chemical reactions by which all living aerobic organisms release the energy stored in their cells.

Thanks to the Krebs Cycle, aerobic organisms (those that need oxygen to live) convert proteins, carbs, and fats to generate energy (in the form of adenosine triphosphate), which is necessary for them to live.

Chemical Recipe for Life on Earth

The citric acid cycle (CAC) has already been explored in the past to formulate a recipe for the origin of life. Researchers tried to imagine primitive life forms developing CAC using the same biological molecules as those existing today.

However, on early Earth, according to TSRI researchers, these molecules were likely very fragile and the ingredients necessary for the CAC to work were unavailable when the planet was a youthful 1 billion years old.

The TSRI team wrote down each of the chemical reactions that make up the citric carbon cycle, and then determined among the ingredients necessary for these reactions those being available on Earth 4 billion years ago.

Their results revealed that, despite the unavailability of certain fundamental elements, the appearance of a life cycle could have taken place. The team identified two non-biological cycles (the HKG and the malonate cycles) that together could have triggered the appearance of a primitive version of the citric acid cycle.

As time went by, biological molecules (like enzymes) became available and replaced the non-biological molecules in the chemical reactions making the CAC more complex and efficient.

“The chemistry could have stayed the same over time, it was just the nature of the molecules that changed,” said Krishnamurthy. “The molecules evolved to be more complicated over time based on what biology needed.”

The TSRI chemical recipe was published in Nature Communications journal.

Do you think this is the key to figuring out the birth date of life on our planet? Or just another piece of the ever-growing biological puzzle? Let us know your thoughts in the comments section below. 

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