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.
Archaean Time (3800 to 2500 million years ago). The atmosphere that existed during Archean time would be toxic to most extant life on our planet. Also, rocks were just beginning to form at the crust of the earth. It is believed that life on earth made its appearance in the seas during Archaean time.