It has recently be demonstrated, through diamond-anvil cell experiments, that it may be possible for methane to be formed within the inner Earth through transformation reactions involving iron oxides, carbonates and water. The pressure and temperature range of these processes can easily be reached by the high-temperature Paris-Edinburgh cell developed for use on the PEARL beam line, and we are proposing to develop a long-term study of the inorganic synthesis of methane. In this first experiment we are proposing tp carry out in situ neutron powder diffraction studies under simultaneous high temperatures and pressures. Our three objectives are to demonstrate that we can obtain quantitative phase faction measurements of this system, compare the behaviour within the large samples that can be achieved on PEARL with diamond anvil cell results, and measure the transformation rates of 3 samples.