A team of chemists from Purdue University in West Lafayette, Indiana have discovered a mechanism that could explain how the fundamental ingredients of living cells were first created in the unimaginably distant past. The scientists say this mechanism can produce peptides, the so-called “building blocks” of primordial life, from inorganic matter in ocean environments, where the first living microorganisms appeared approximately 3.7 billion years ago.
All the plant and animal life currently existing on the planet can be traced back to these incredibly distant beginnings, to the very first stirrings in the primordial soup . But significant questions remain about how exactly life formed from nothing, or more specifically from the mixture of non-living compounds that would have been found in ancient seas.
Secrets to understanding the origin of primordial life discovered in droplets from sea spray. ( Anton Maltsev / Adobe Stock)
The Origins of Primordial Life on Earth
In an article published in the Proceedings of the National Academy of Sciences (PNAS), Purdue University scientists explain that “conditions that permit the abiotic production of peptides in aqueous environments are a prerequisite for accepted origin-of-life chemistry.” Working from this premise, the biochemists were thrilled to discover what they term “a unique reactivity of free amino acids at the air-water interface of micron-sized water droplets that leads to the formation of peptide isomers on the millisecond timescale.”
In their reference to “air-water interface of micron-sized water droplets,” what they are describing is the creation of sea spray, the foamy conglomeration of white air bubbles that forms on top of the water when ocean waves crash into beaches or rocky shorelines. The scientists discovered a special chemical reaction in sea spray that creates peptides from free amino acids, which is critically important since something equivalent to this would be needed to explain how life developed in primitive oceans.
“This is essentially the chemistry behind the origin of life ,” Graham Cooks, a Professor of Analytical Chemistry at Purdue, said in a Purdue University press release . “This is the first demonstration that primordial molecules, simple amino acids, spontaneously form peptides, the building blocks of life, in droplets of pure water,” he stressed. “This is a dramatic discovery.”
Graham Cooks has studied the chemistry of water droplets for decades, discovering insights into cancer detection, drug discovery and the origins of primordial life through early Earth chemistry. (Andrew Hancock / Purdue University )
Tracing the Ancient Evolutionary Pathway
Peptides are made from short chains of amino acids, and may contain anywhere from two to 50 of these molecules. Along with proteins, they are the fundamental components of microbial, plant, and animal cells, performing a range of indispensable biological functions. Proteins are actually made from large and complex peptide structures, which makes peptides essential to the whole construction of a living cell.
Amino acids did not have to evolve spontaneously to appear on Earth. Raw amino acids are constantly deposited on Earth by meteorite strikes , a phenomenon that occurred much more frequently billions of years ago.
However, free-floating amino acids wouldn’t have easily consolidated into peptides in ancient oceans. The problem is that when amino acids interlock to create peptides they must shed a water molecule to do so, which would be impossible if the amino acids were fully immersed in water. The conversion process would have required water at the beginning, but at some point the amino acids would need to have been liberated from the water to form peptides.
This is where sea spray in a primordial sea would have come to the rescue. The air bubbles in the spray would have carried amino acids to the surface of the ocean, where these bubbles would have burst and released rapidly moving streams of water droplets that would have facilitated an interaction between amino acids and chemicals in Earth’s atmosphere. When those droplets meet the atmosphere exceptionally fast chemical reactions take place, and that could have created peptides out of abiotic strings of amino acids.
The Purdue University chemists have been using mass spectrometers for more than a decade to study chemical reactions in water droplets. Their equipment generates artificial sea spray in the laboratory, mimicking what happens in nature. “The rates of reactions in droplets are anywhere from a hundred to a million times faster than the same chemicals reacting in bulk solution,” Professor Cooks said.
Because these reactions progress so quickly, they make the addition of additional catalysts unnecessary. Occurring in Earth’s oceans billions of years ago, such reactions would have enabled the eventual evolution of primordial life, following a pathway from amino acid to peptide to protein to DNA and beyond.
Meteor hitting earth’s atmosphere. Scientists believe that the chemical elements required for the origin of primordial life came to Earth with asteroids and comets. ( James Thew / Adobe Stock)
Speeding the Pace of Evolution and Scientific Discovery
It should be noted that in this particular experiment, mass spectrometry analysis did show that simulated sea spray could create peptides spontaneously. But the sea-spray-induced molecules induced in the Purdue laboratory were exclusively dipeptides, which contain only two amino acids, the minimum number possible in a peptide.
It is assumed that the process of amino acid conglomeration triggered by sea spray in primordial oceans would have generated a more diverse and complex range of peptides than this, as would be required for life to ultimately form. But the Purdue University chemists have found only the most elemental types of peptides in the experiments they’ve performed up to this point.
This experimental result is still remarkable and represents a breakthrough in knowledge about what is possible, versus what is only theoretical. In addition to offering insights on the likely origin of primordial life , the discoveries of the Purdue University scientists may also have medical applications. Fast chemical reactions in simulated sea spray could conceivably be controlled and customized, perhaps to create brand new medications.
“If you walk through an academic campus at night, the buildings with the lights on are where synthetic chemists are working,” Professor Cooks said. “Their experiments are so slow that they run for days or weeks at a time. This isn’t necessary, and using droplet chemistry, we have built an apparatus, which is being used at Purdue now, to speed up the synthesis of novel chemicals and potential new drugs.”
Top image: New study suggests primordial life originated in sea spray. Source: Rysak / Adobe Stock
By Nathan Falde