Diamonds May Be Life's Birthstone
One of the hurdles in origin of life theories is that the pieces that make up complex biomolecules do not readily come together by themselves. A group of scientists proposes that diamonds provided a kind of "work bench" for biomolecule manufacturing on early Earth.
Not long after its formation, our planet was – according to astrobiologists – awash in a primordial soup that contained the rudimentary ingredients of life. The fly in the "soup" theory, however, is that the small molecular bits likely needed outside help in order to latch together into the long, complex biomolecules that living organisms use.
Some scientists have suggested that the surfaces of minerals on the early Earth provided an organizing platform upon which the building blocks of life could assemble. Recent studies of diamond suggest that its surface would be especially good for this.
"Diamond is totally non-toxic, an excellent biomaterial and certainly the only naturally existing material that is completely biocompatible on all levels – presumably the best of all possible platforms for the formation of life," said Andrei Sommer from the University of Ulm in Germany.
Sommer and his colleagues discovered that a certain type of diamond, called hydrogenated diamond, imposes a rigid order on molecules near its surface. They suggest, in a recent issue of the journal Crystal Growth and Design, that this diamond-mediated order helped fit together the pieces that led to the emergence of life.
Frozen with fear
Hydrogenated diamonds are just diamonds with an outer coating of hydrogen atoms, but they are not something you’ll find in your local jewelry shop. In fact, the only hydrogenated diamonds currently known are all made in the lab.
"In nature, diamond hydrogenation is likely to occur in or in the vicinity of volcanoes known to emit a variety of hot gases including hydrogen," Sommer said. The early Earth had so much volcanic activity that he thinks it is highly probable that hydrogenated diamonds existed back then.
Sommer and his collaborators previously showed that hydrogenated diamond is very hydrophobic, or "water fearing" — meaning it pushes water away. When hydrogenated diamond is wetted, the water molecules line up on the surface as if they were frozen into a crystal layer (an analogy might be static electricity making all the hairs on your head point out).
Surprisingly, these crystal water layers do not disappear when the hydrogenated diamond is fully immersed in water. Because this is the only natural material known to exhibit this behavior, Sommer’s team proposes that small organic molecules in the primordial soup landed on hydrogenated diamond and were helped by its robust crystal water layers into linking together to form proteins and DNA.
Support for this idea comes from a recent study that found that certain nucleobases (the building blocks of DNA and RNA) form an organized pattern on the surface of graphite, which is chemically similar to diamond.
Hydrogenated diamond should be a better organizing platform than graphite, Sommer said. This is because the crystal layers that form on it are not static; they change with temperature and light intensity. The resulting fluctuations could have helped drive the development of novel molecules in the primordial soup.
"So far, crystal water layers have only been described on hydrogenated diamond," said Horst-Dieter Foersterling of Philipps University of Marburg, who was not involved with this work. "This is a new field of research. That this system can be helpful for the formation of biomolecules is a plausible hypothesis."
It remains uncertain whether there was any hydrogenated diamond on Earth billions of years ago, but even a little bit might be enough.
"I think it is not important that a lot of hydronenated diamond was available," Foersterling said. "Once the first evolution process has started in a very special location [such as a tiny patch of hydrogenated diamond], and stable DNA strands have formed, a special location is no more necessary."