It is measure of how many different species exist in an area at a given time. There are various ways to calculate diversity, and the best way to measure it is a cause of arguements amongst scientists still. The study of how organisms interact with each other and their physical environment. To do this ecologists look at ecosystems. All the members of a biological community and the physical environment the community exists in.
Nutrients move around ecosystems in loops.
Material is then returned to the soil by animal waste and bacteria that decompose carcasses. It lasted from 190 Ma until 140 Ma. Named after the Jura mountains on the Swiss-French border. This is famous because it marks the end of the 160 Ma reign of the dinosaurs and related archosaurs. There is strong evidence that a bolide impacted on the Earth just off the coast of Mexico at this time, but there is growing evidence that this acted as the final straw to the dinosaurs, which had been gradually declining anyway.