GEOLOGY

Detailed explanation-1: -The oldest known fossils, in fact, are cyanobacteria from Archaean rocks of western Australia, dated 3.5 billion years old. This may be somewhat surprising, since the oldest rocks are only a little older: 3.8 billion years old! Cyanobacteria are among the easiest microfossils to recognize.

Detailed explanation-2: -Today, scientists use a variety of techniques to date rocks and fossils precisely. Most often, they measure the amounts of particular radioactive elements-often radiocarbon or potassium-present to determine when a rock was formed, or when an animal or plant died.

Detailed explanation-3: -Since the rock formation contains both types of fossils the ago of the rock formation must be in the overlapping date range of 415 to 420 million years. Studying the layers of rock or strata can also be useful. Layers of rock are deposited sequentially.

Detailed explanation-4: -The bottom layer of rock forms first, which means it is oldest. Each layer above that is younger, and the top layer is youngest of all. This ordering is relative because you cannot be sure exactly when each layer formed, only that each layer is younger then the one below it.