We can't use both. The answer is to use the one with the smaller absolute value: With this definition of. A slightly different formal definition of the limit is used when x goes to +/- infinity, since we really cannot subtract x from infinity or vice versa-remember, infinity is a concept, not a number. Formally, the expression. Means that.
During the long interval of the Precambrian Era (which includes approximately 90% of geologic time and includes three Eons: the Hadean, the Archean and the Proterozoic) the only inhabitants of the Earth were simple microscopic organisms, many of them comparable in size and complexity to modern-day bacteria.
245 to 208 million years ago. 1  During the Triassic period, all land on Earth existed as one enormous mass. It was called Pangaea. 2  Some reptiles, frogs, turtles and crocodiles existed earlier, but dinosaurs didnât appear until late in the Triassic period. 3  The period marked the rise of small, lightly built dinosaurs. The first mammals evolved during the Triassic period. Most of the plants that existed were evergreens. The period ended with a mass extinction that wiped out most animals and reptiles. An entire order of plants or animals dies out in a mass extinction. The dinosaurs that survived flourished in the next period, the Jurassic. Dinosaurs that lived during the Triassic period include: