Scientists have had a basic understanding of how life first popped up on Earth for a while. The so-called “primordial soup” was sitting around, stagnant but containing the basic building blocks of life. Then magic happened and we ended up with life. It’s that “magic” that has been the sticking point for scientists, but new research from a team of scientists at the University of Leeds has started to shed light on the mystery, explaining just how objects from space might have kindled the reaction that sparked life on Earth.
It’s generally accepted that space rocks played an important role in life’s genesis on Earth. Meteorites bombarding the planet early in its history delivered some of the necessary materials for life but none brought life as we know it. How inanimate rocks transformed into the building blocks of life has been a mystery.
But this latest research suggests an answer. If meteorites containing phosphorus landed in the hot, acidic pools that surrounded young volcanoes on the early Earth, there could have been a reaction that produced a chemical similar one that’s found in all living cells and is vital in producing the energy that makes something alive. The unusual phosphorus chemicals could be a precursor to the “batteries” that now power all life on Earth. And that this “battery” could develop in conditions similar to those on the young Earth suggests this could be the missing link in how space rocks become life-giving rocks.
Flashback to high school biology class. All life on Earth is powered by a process called chemiosmosis. The chemical adenosine triphosphate (ATP) is broken down and re-formed during respiration to release the energy units that drive metabolism. Simply, ATP is the battery that charges the reactions that make something alive.
The problem for scientists has long been that the enzyme that both breaks down and rebuilds ATP is complex, far too complex to have existed on the early Earth. So scientists started looking for a substitute, a more basic chemical with similar properties to ATP that doesn’t need an enzymes to transfer energy.
A schematic showing the process of ATP breaking down to yield energy. via
Phosphorus is the key element in ATP. But the form most commonly found on Earth is insoluble in water and has a low chemical reactivity. Not a great candidate. But the early Earth was different. It was regularly bombarded by meteorites rich in exotic minerals like the far more reactive form of phosphorus, an iron-nickel-phosphorus mineral schreibersite.
The team from Leeds tested their theory by simulated a phosphorus rich meteorite impacting the hot, volcanically-active early Earth. They put a sample of the Sikhote-Alin meteorite, an iron meteorite that fell in Siberia in 1947, in acid taken from the Hveradalur geothermal area in Iceland. They left the rock in the acidic fluid for four days, then took it out and left it at room temperature.
Analyzing the resulting solution, the team found the compound pyrophosphite. Pyrophosphite is a molecular ‘cousin’ of pyrophosphate, the part of ATP responsible for energy transfer. This chemical compound, the team thinks, might have acted as an early form of ATP, a for they’re calling “chemical life.”
This chemical life would have been the intermediate step between inorganic rock and the very first living biological cell. And you can think of it sort of like a robotic rover (figuratively, not literally). Chemical life can move and react to its surrounding, but it’s not properly alive. But this primitive life-ish chemical could have organized the chemicals in the primordial soup in such a way that they could support more complex behaviour. Ultimately, put in the right order, the chemicals could have developed into living biological structures.
Artist's concept of the early Earth, molten and bombarded by phosphorus-rich meteorites. via
So this story gets even better. The science team behind NASA’s Curiosity rover has found evidence of the same phosphorus on Mars. If it turns out that Curiosity has found phosphorus in one of the forms the Leeds team produced in their simulations, it will be good evidence that early Mars could have supported the same kind of life as early Earth.
The Leeds team is now working with scientists from JPL and Caltech to figure our just how these early batteries and the ‘chemical life’ developed into biological life. To answer this question, they’re going to build a ‘geological fuel cell’ using minerals and gases common on the early Earth then apply different chemicals to its surface. They’ll monitor the reactions and see what chemical products develop. The team also plans to repeat their initial experiment n Disko Island in Greenland, the only place on Earth with a naturally-occurring source of schreibersite, which is the reactive mineral found in the Sikhote-Alin meteorite.
So there’s still more work to be done to build on these initial results, but it’s looking pretty awesome so far.