Today, James and I mainly discussed some of the chemical and physical properties of the earth. First, we looked at the various characteristics of plate techtonics and the differing types of tectonic plate boundaries. We correlated the formation of mountains and deep oceanic trenches with the different types of plate movement. We discussed the layers of the atmosphere and the various characteristics that make these layers unique. We also talked about chemical and physical weathering, and the role carbonic acid plays in weathering stone, minerals, and metals. I reiterated to Graham the differences between ions and isotopes and how some isotopes can be used to determine relative dates of rocks, minerals, and fossils.