How did life get started on Earth? Atmospheric haze might have been the key

A recent study accepted to The Planetary Science Journal and currently posted to the arXiv preprint server investigates how the organic hazes that existed on Earth between the planet's initial formation and 500 million years afterwards, also known as Hadean geologic eon, could have contained the necessary building blocks for life, including nucleobases and amino acids. This study holds the potential to not only help scientists better understand the conditions on an early Earth, but also if these same conditions on Saturn's largest moon, Titan, could produce the building blocks of life, as well.

Here, Universe Today discusses this recent study with Dr. Ben K. D. Pearce, who is a Postdoctoral Fellow in the Morton K. Blaustein Department of Earth & Planetary Sciences at Johns Hopkins University and lead author of the study, regarding the study's findings, potential follow-up research, NASA's upcoming Dragonfly mission to Titan, and whether he thinks there's life on Titan.

Dr. Pearce tells Universe Today about how past lab studies involving Carl Sagan discovered that the highest dilution (or addition of a solvent like water) to make the chemical reactions work was 100 micromolar, or approximately 10 parts per million (ppm). If the dilution is too strong, the molecules in the chemical mixture wouldn't find each other, he says.

"After all, early Earth was a hazy place, much akin to Saturn's moon Titan," Dr. Pearce tells Universe Today. "This is because over 4 billion years ago, Earth had an atmosphere rich in hydrogen, methane, and nitrogen, similar to Titan! What's interesting about these haze particles, is that they are essentially biomolecule snowflakes, i.e., big aggregates of life's building blocks bonded together. When these particles settled onto Earth's surface, over 4 billion years ago, and fell into ponds, the bonds would break, and you could get a pond rich in life's building blocks. We wanted to know if this source could exceed the 100 micromolar threshold in ponds, which could be concentrated enough for them to react and begin the process of forming the first information molecules like ribonucleic acid (RNA)."

For the study, the researchers created organic hazes in a laboratory setting under atmospheric conditions containing between 0.5% and 5% methane and analyzed the hazes for traces of amino acids and nucleobases using a gas chromatograph/mass spectrometer (GC/MS). Additionally, they heated samples up to 200°C (392°F) to simulate the samples resting on an uninhabitable surface, as well. The team then compared their results to computer models to investigate the number of nucleobases that would be present in these same environments.

"When we modeled the pond concentrations of nucleobases from organic hazes (making use of our experimental data), we discovered that this source may be the richest, most long-lasting source that we've modeled to date," Dr. Pearce tells Universe Today. "As a reminder, all sources we've studied to date (meteorites, interplanetary dust, and atmospheric HCN) have led to below 100 micromolar concentrations; however, now we have finally found a source that breaches up towards this threshold."

In the end, the team discovered that nucleobases could exist in "warm little ponds" on Earth during the Hadean geologic eon. With the heating experiment, the team ascertained that such samples could not survive on a hot surface. Finally, they concluded that organic hazes could produce the building blocks of life only in a methane-rich atmosphere on ancient Earth, "but not so rich as to create an uninhabitable surface," Dr. Pearce notes to Universe Today. Given these incredible findings, what follow-up research is being conducted or planned?