Could life on Earth have taken a completely different form, based on the “handedness” of its chemical building blocks?
A new study by researchers at UCLA and NASA’s Goddard Space Flight Center sheds light on this fascinating question.
What is chirality?
In chemistry, molecules can exist in two forms that are mirror images of each other, like your left and right hands. This property is called chirality.
On Earth, all life uses “right-handed” sugars and “left-handed” amino acids as the building blocks of DNA, RNA, and proteins. These specific forms, known as enantiomers, dominate life as we know it.
However, their mirror-image counterparts could, in theory, also support life.
The researchers wanted to understand if life on Earth was always destined to favor one “handedness” over the other, or if it could have started differently.
The study, published in Nature Communications, focused on the early Earth period often referred to as the “RNA world,” about 4 billion years ago. During this time, single-stranded RNA molecules likely played a crucial role in the development of life.
To investigate, the team conducted experiments with ribozymes—small pieces of RNA that can catalyze chemical reactions.
They created a solution simulating early Earth conditions, combining ribozymes with amino acid precursors to see if the ribozymes preferred one type of amino acid handedness.
The surprising result? The ribozymes were flexible. They could produce both left- and right-handed amino acids, depending on the ribozyme.
This finding suggests that early RNA may not have had a built-in preference for left-handed amino acids, challenging the idea that life was chemically predetermined to take its current form.
“This study suggests that life as we know it wasn’t inevitable,” said study leader Irene Chen. “RNA on early Earth might have built either type of amino acid, opening up the possibility that life could have developed very differently.”
Instead of chemical determinism, the researchers believe evolutionary pressures might have later pushed life toward using only left-handed amino acids in proteins.
The study also has implications for finding life beyond Earth. Understanding the flexibility of RNA and amino acids helps researchers know what to look for when searching for extraterrestrial life.
NASA’s Jason Dworkin, a co-author of the study, highlighted this connection. “We are analyzing samples from asteroids like Bennu for signs of chirality in amino acids. Future missions to Mars may also test for evidence of life, including RNA and proteins.”
This research reveals that the building blocks of life are more adaptable than previously thought, offering a glimpse into the origins of life—and the possibilities for life beyond Earth.
Source: UCLA.
