2. The Geology of Kerogen (From the stars to planet Earth. Mars geology and kerogen in the mantle)
Kerogen, as defined by Alexander Crum Brown in the 1840s, is purely descriptive and does not carry the modifier ‘organic’ as it simply means the carbonaceous matter in black shales. Primordial kerogen refers to the universality of kerogen as is occurs in stars, planets, Mars, planetary mantles, and meteorites. Hydro-kerogen refers to kerogen that has interacted with water, thus adding hydrogen from water to enhance the amount of hydrogen in kerogen, in a process called hydrogenation. This kerogen (usually the TOC term in chemical analyses of rocks) occurs in many rock types, such as in mantle xenoliths, peridotite, serpentine, rodingite, talc, and others. Kerogen is both old rocks, occurring in Precambrian rocks before there was life on Earth, and in recent rocks.