It can be in the form of coal, or more commonly fine particles. A great deal of carbon escapes to sediments in the sea in the form of actual particles of carbon-rich organic matter. The amount of organic carbon that get buried is, however, only a very small fraction of what is present as living tissue at any one time. The lithosphere consists of relatively rigid plates floating on a more plastic asthenosphere. Plates are often composed of both areas of oceanic and continental lithosphere.
All lithosphere is composed of two layers of differing composition.
Calcium in continental crust is what is important for the carbon cycle. The lower layer of the lithosphere is made up primarily of magnesium, silicon, and oxygen and comprises the upper mantle. The subducting plate often carries with it sediment laid down in the oceans and the sediment too eventually melts. The lava from this melt of the subducting plate is rich in CO2, calcium and water vapor. When the lava, ash, and unerupted magma hardens, it adds to the continental crust, in part replacing the material which is lost from the continental crust by erosion.