One nitrogen atom, three hydrogen atoms. That’s all it takes to make the basic ammonia molecule. This simple compound was one of the most important building blocks for the origin of life, scientists believe, providing the nitrogen that is crucial to many organic compounds. They just don’t know for sure how so much of it could form under the conditions of the early Earth.
In a new study this week, Sandra Pizzarello and colleagues tie the ammonia surplus to one of the more fascinating theories about the rise of life—that some of its basic components seeded the Earth from space on board meteorites that pounded the planet’s surface.
Pizzarello’s team analyzed a particular meteorite found in Antarctica. Its name is Graves Nunataks (GRA) 95229, and it was discovered in 1995. But its important characteristic is that the it belongs to a class of meteorites called carbonaceous chondrites that are full of organic materials. In the lab, the researchers tried to simulate how those materials in GRA 95299 might have reacted when they reached the younger Earth.
Pizzarello and her co-authors subjected a sample of the meteorite … to temperatures of 300 degrees Celsius at high pressures in the presence of water to simulate hydrothermal conditions on the meteorite’s parent asteroid or on Earth. Under heat and pressure, GRA 95229 released almost nothing but ammonia, in amounts that constitute roughly 1 percent by mass of the type of meteoritic material examined. Its parent asteroid, the authors speculate, must have been rich in ammonia. [Scientific American]
Some of the consequences of ocean acidification appear obvious: The shells of mollusks, for instance, could dissolve as the pH of ocean water drops thanks to the ocean pulling out some of the excess carbon dioxide humans put into the atmosphere. But what about more subtle effects of seawater growing more acidic?
In the Proceedings of the National Academy of Sciences this week, researchers set up an experiment to see whether the growing acidity of the ocean could disrupt the marine cycle of nitrogen, which provides key nutrients for plant life. Indeed it can, J. Michael Beman’s team found, and that’s another potentially dangerous side effect of the ocean as a carbon sink.
The authors of the study examined a specific step in the marine nitrogen cycle, called nitrification, in which microorganisms convert one form of nitrogen, ammonium, into nitrate, a form plants and other marine microorganisms require to survive. Previous research studies on experimentally acidified freshwater … in the laboratory have suggested that reduced pH slows nitrification, and one study in coastal ocean waters showed that large pH decreases did the same. [Scientific American]
So Beman sought to test the ocean by gathering samples of seawater from locations around the world and adding CO2 to simulate what will be happening to the oceans in the coming decades. Just decreasing the pH from 8.1 to 8.0 resulted in about 20 percent less nitrate creation, the team wrote. In their experiments that lowered pH between .05 and .14, the nitrate production dropped between 8 and 38 percent.