Third, magnetism in rocks can be used to estimate the age of a fossil site. This method uses the orientation of the Earth's magnetic field, which has changed through time, to determine ages for fossils and rocks.
Some animals, particularly ruminants and termites, can digest cellulose with the help of symbiotic micro-organisms that live in their guts, such as Trichonympha. In humans, cellulose acts as a hydrophilic bulking agent for feces and is often referred to as a  dietary fiber .
Foods such as potatoes, rice, corn and wheat contain starch granules which are important energy sources for humans. The human digestive process breaks down the starches into glucose units with the aid of enzymes, and those glucose molecules can circulate in the blood stream as an energy source.