Reactions between organic acids and montmorillonite clay under Earth-forming conditions

The stability and evolution of organic materials found in carbonaceous and ordinary chondrites in the evolution of terrestrial planet interiors are unknown. It has been determined that massive amounts of carbonaceous material fell on the early Earth during the Late Hadean, but the processes by which this material became the Earth's hydrosphere, atmosphere and biosphere are also unknown. We here demonstrate that reactions between these primordial organic molecules and the silicate mineral montmorillonite clay occur at the pressures associated with the upper mantle and planetary assembly. These reactions have consequences for the origin of complex organic chemistry on Earth. Using synchrotron-source Fourier transform infrared (FTIR) spectroscopy with high spatial resolution and the diamond anvil cell (DAC) to reach pressures up to 9.1 GPa, we were able to observe the formation of new peaks (i.e., new bonds) at 952, 969, and 1026 cm−1 in situ. These peaks, which appear in formic acid (HCOOH) in the presence of montmorillonite clay, may represent either the formation of organo-silicate molecules, or the formation of more complex organic molecules via templating of the crystalline structure of the minerals.