Removing traces of life in the lab helps NASA scientists study its origins

Last year, researchers at JPL’s Origins and Habitability Lab simulated the chemistry of the early Earth and performed a key chemical reaction involved in metabolism, the process living organisms use to convert fuel (such as sunlight or food) into energy. Did Earth’s first life forms create energy with the same chemical reactions used by living organisms today?

The first step in answering that question is to determine whether these reactions were even possible on early Earth. In living organisms, such reactions take place only inside a membrane (like the protective wall of a living cell), which is just one reason why it is an open question whether – and how – these reactions could have occurred before life formed.

In JPL’s Origins and Habitability Lab, researchers use a sealed chamber to conduct experiments free of oxygen in an attempt to recreate the chemistry of the early Earth. From left are laboratory co-director Laurie Barge and researchers Jessica Weber and Laura Rodriguez. Credit: NASA/JPL-Caltech

The laboratory’s work belongs to a discipline known as astrobiology: the study of the origin, evolution, distribution and future of life in the universe. The threads are connected, so trying to understand how life formed on Earth will also help scientists search for life elsewhere. In fact, in another study, the lab team explored how understanding the origins of life on Earth can also help scientists interpret the appearance of organic molecules (the chemical basis of living things on Earth) that might be found on another planet or moon.

But simulating the conditions on Earth before life appeared is no easy task. Turning back the clock means paying attention to how life has transformed our planet.

Something in the air

There really isn’t a place on Earth that isn’t occupied by some form of life. Microorganisms can be found at the bottom of the ocean, in burning hot geysers, and in rooms dedicated to removing these organisms.

Life forms have also transformed the planet’s chemistry. One of the biggest challenges in trying to create pre-life conditions in the laboratory is dealing with the presence of oxygen. Largely absent from Earth’s atmosphere before life appeared, it is now ubiquitous because so many life forms produce it. As a result, all of the lab’s origin-of-life experiments must be conducted in an airtight box, with an airlock to put objects in or take them out. In addition to test tubes containing chemicals, all instruments used to analyze these chemicals must fit inside the box, so there are some experiments the team cannot do in this setting.

Also, only one person can work in the box at a time, donning thick rubber gloves built into the sides of the container to move things around or use the equipment. Filters (which require regular cleaning) catch stray oxygen atoms. Even water has to go through a long process to remove oxygen gas.

“Science is about repetition,” said JPL scientist Laurie Barge, who directs the Origins and Habitability Lab. “We want to do experiments again and again, and that’s hard to do when you have to spend so much time making sure that not even a tiny bit of oxygen has snuck into your test tube.”

It took Barge and her team months to demonstrate that one chemical reaction involved in modern metabolism could take place under these early Earth conditions. They plan to continue trying to simulate each step of the metabolic process, and at some point they may find that a certain reaction can only occur inside a protective structure like a membrane. It may help to constrain when membranes became necessary in the emergence of life – a glimpse back in time.

There’s another way scientists can learn about the chemistry that took place, potentially setting the stage for life on Earth: By studying a planet or moon with roughly the same raw ingredients that would have been found on early Earth. The location could be a lifeless moon in our own solar system or a planet around another star. Then Barge and her colleagues could test the ideas they are investigating against an environment not limited to the size of a glove compartment.

“It would be very interesting to validate and check some of our lab results against results from another world,” said Jessica Weber, a JPL scientist in the Origins and Habitability Lab who led the metabolism work. “Finding an environment like this will help us better recreate the early Earth in our laboratory experiments, and it will bring us closer to answering some of the big questions about life on our own planet and potentially on others.”

References: “Determining the “Biosignature Threshold” for Life Detection on Biotic, Abiotic, or Prebiotic Worlds” by Laura M. Barge, Laura E. Rodriguez, Jessica M. Weber, and Bethany P. Theiling, 13 Apr. 2022, Astrobiology.
DOI: 10.1089/ast.2021.0079

“Testing Abiotic Reduction of NAD⁺ Directly Mediated by Iron/Sulphur Minerals” by Jessica M. Weber, Bryana L. Henderson, Douglas E. LaRowe, Aaron D. Goldman, Scott M. Perl, Keith Billings and Laura M. Barge, 11 Jan 2022, Astrobiology.
DOI: 10.1089/ast.2021.0035