NEW DELHI (TIP): A new report by Nasa scientists puts together decades of research to provide first evidence that life on Earth may have started on the sea floor, billions of years ago. In this “water world” theory, life may have begun inside warm, gentle springs on the sea floor, at a time long ago when Earth’s oceans churned across the entire planet.
This is in contrast to an earlier theory that life may have begun near vents bubbling with hot acidic fluids. The new study comes from researchers at Nasa’s Jet Propulsion Laboratory and the Icy Worlds team at Nasa’s Astrobiology Institute. It is published in the April issue of the journal Astrobiology. The water world theory from Michael Russell and his team at JPL says that the warm, alkaline hydrothermal vents created an imbalance with respect to the surrounding ancient, acidic ocean.
This imbalance could have provided so-called free energy to drive the emergence of life. In fact, the vents could have created two chemical imbalances. The first was where protons — which are hydrogen ions — were concentrated more on the outside of the vent’s chimneys, also called mineral membranes. The proton gradient could have been tapped for energy — something our own bodies do all the time in cellular structures called mitochondria.
The second imbalance could have involved an electrical gradient between the hydrothermal fluids and the ocean. Billions of years ago, when Earth was young, its oceans were rich with carbon dioxide. When the carbon dioxide from the ocean and fuels from the vent — hydrogen and methane — met across the chimney wall, electrons may have been transferred. These reactions could have produced more complex carbon-containing, or organic compounds — essential ingredients of life as we know it.
Like proton gradients, electron transfer processes occur regularly in mitochondria. “Within these vents, we have a geological system that already does one aspect of what life does,” said Laurie Barge, second author of the study at JPL. “Life lives off proton gradients and the transfer of electrons.” As is the case with all advanced life forms, enzymes are the key to making chemical reactions happen. In our ancient oceans, minerals may have acted like enzymes, interacting with chemicals swimming around and driving reactions.
In the water world theory, two different types of mineral “engines” might have lined the walls of the chimney structures. “These mineral engines may be compared to what’s in modern cars,” said Russell. “They make life ‘go’ like the car engines by consuming fuel and expelling exhaust. DNA and RNA, on the other hand, are more like the car’s computers because they guide processes rather than make them happen.”
One of the tiny engines is thought to have used a mineral known as green rust, allowing it to take advantage of the proton gradient to produce a phosphatecontaining molecule that stores energy. The other engine is thought to have depended on a rare metal called molybdenum. This metal also is at work in our bodies, in a variety of enzymes. It assists with the transfer of two electrons at a time rather than the usual one, which is useful in driving certain key chemical reactions.
“We call molybdenum the Douglas Adams element,” said Russell, explaining that the atomic number of molybdenum is 42, which also happens to be the answer to the “ultimate question of life, the universe and everything”” in Adams’ popular book, “The Hitchhiker’s Guide to the Galaxy.” Russell joked, “Forty-two may in fact be one answer to the ultimate question of life!”