A typical example of a class. This one is part of the Mesozoic era of evolutionary biology. It is one of 24 classes that covers what life is, how life first began during the Archean eon and the evolution of animals and plants through the periods from the Cambrian right through to the Quaternary. Classes contain advanced vocabulary, interesting images, diagrams to help explain concepts and videos to fill in the mental gaps and offer the student time to absorb the material and generate ideas.