Origin of Life?

Researchers at the University of Leeds may have solved a key puzzle regarding how materials from space could have sparked the emergence of life on Earth.

While it is widely accepted that some essential ingredients for life were delivered to the early Earth by meteorites, scientists have long struggled to explain how inanimate rock transformed into the fundamental building blocks of living organisms.

This new study demonstrates how a chemical similar to one found in all living cells today—and essential for generating the energy required for life—could have formed when meteorites containing phosphorus-rich minerals landed in hot, acidic pools near volcanoes, environments that were likely common on the early Earth.

“The mystery of how living organisms emerged from lifeless rock has puzzled scientists for decades,” said Dr. Terry Kee of the University of Leeds’ School of Chemistry, who led the research. “We believe that the unusual phosphorus compounds we discovered could have been precursors to the chemical batteries that power all life on Earth today. The fact that these compounds formed naturally under conditions similar to those on the early Earth suggests they may represent the missing link between geology and biology.”

All life on Earth is powered by a process known as chemiosmosis, in which the chemical adenosine triphosphate (ATP)—the rechargeable molecular “battery” of life—is continuously broken down and regenerated during respiration. This process releases the energy required to drive metabolism and other life-sustaining reactions. However, the complex enzymes necessary for ATP synthesis and breakdown are unlikely to have existed when life first emerged. Consequently, scientists have searched for a simpler energy-transferring chemical with properties similar to ATP but not dependent on enzymes.

Phosphorus is a key component of ATP and other essential biological molecules such as DNA. However, the most common form of phosphorus on Earth, phosphorus(V), is largely insoluble in water and chemically unreactive. In contrast, the early Earth was frequently bombarded by meteorites and interstellar dust containing exotic minerals, including Schreibersite, an iron-nickel-phosphorus mineral that is far more chemically reactive.

To investigate this possibility, researchers simulated the interaction between such meteorites and the hot, volcanically active environment of the early Earth. They placed samples of the Sikhote-Alin meteorite—an iron meteorite that fell in Siberia in 1947—into acidic water collected from the Hveradalur geothermal area in Iceland. The samples were incubated in the geothermal environment for four days and then kept at room temperature for an additional thirty days.

Analysis of the resulting solution revealed the presence of pyrophosphite, a molecular relative of pyrophosphate, the ATP component responsible for energy transfer. The researchers believe that pyrophosphite may have served as a primitive predecessor to ATP in what they describe as “chemical life.”

“Chemical life would have represented an intermediate stage between inorganic rock and the first living biological cells,” explained Dr. Kee. “One way to think about chemical life is as a machine. A robot, for example, can move and respond to its environment, but it is not alive. With the aid of these primitive chemical batteries, molecules may have become organized into systems capable of increasingly complex behavior, eventually evolving into the biological structures we observe today.”

Scientists at NASA’s Jet Propulsion Laboratory (JPL-Caltech), working on the Curiosity rover, which landed on Mars in August 2012, have also reported the presence of phosphorus on the Red Planet.

“If Curiosity has detected phosphorus in one of the forms we produced in Iceland, it may indicate that conditions on Mars were once suitable for the development of life in a manner similar to what we now believe occurred on Earth,” Dr. Kee added.

The Leeds research team is currently collaborating with colleagues at JPL-Caltech to investigate how these early chemical batteries and the forms of “chemical life” associated with them may have evolved into biological life. As part of this work, researchers will use facilities within the University of Leeds’ Faculty of Engineering—normally employed for testing advanced fuel cells—to construct a ‘geological fuel cell’ using minerals and gases common on the early Earth. Various chemicals will be applied to its surface, and the resulting reactions and products will be closely monitored.

The team also plans to travel to Disko Island, Greenland, home to the Earth’s only naturally occurring source of Schreibersite, the mineral found in the Sikhote-Alin meteorite. There, they hope to repeat their experiments and demonstrate that the same chemical processes can occur in a completely terrestrial environment.