Biological clocks allow organisms to assess and respond to the oscillating environmental rhythms that result from the Earth's movements via the generation of biological rhythms.
Environmental rhythms are things like day and night and the rise and fall of the tides.
This is responsible for the generation of other 24 hour rhythms, one of the most significant of these being the light-dark cycle. As we shall see later the light-dark cycle is influential in the establishment and maintenance of many other rhythms e.g. locomotor activity patterns. Movement of the Earth around the Sun. Movement of the Moon around the Earth . Many organisms have rhythms that correspond to these periods.