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.
) as the modern period in the life of Gaia (following the Archean and the Proterozoic), the maturity or third age of Gaia so to speak, and is characterized as much, if not more, by the presence of abundant free oxygen as by the existence of multicellular organisms or fossil-bearing rock strata.