What is the function of a pacemaker in the heart?

What is the importantence of the carbon and nitretan cycles in the environment

The intervention of extraterrestrials has been used to explain the bermuda triangle, a region of the atlantic ocean where ships and planes are frequently lost, leaving no evidence behind. how would this explanation best be characterized?

Explain how paleontologists use trilobite fossils as index fossils for various geologic time periods.