Students learned in detail about how decaying organic plant material gets preserved over time (taphonomy). For example, plants can get preserved under volcanic ash, mud slides, or on lake and river bottoms. In all cases, fine sediment or ash completely covers the plant material. To illustrate taphonomy, students went to the river to look at some sediment. Students shoveled mud into large screens, or sieves, to separate any decaying organic material that was destined to become a fossil in the far future.