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.
In fact, geologists define the beginning of the Archean era as the age of the oldest rocks on Earth we can still find today. Proterozoic (Early Life) Era Well, here we are about 700 million years ago, near the end of the longest time period in geologic history.n fact, geologists define the beginning of the Archean era as the age of the oldest rocks on Earth we can still find today. Proterozoic (Early Life) Era Well, here we are about 700 million years ago, near the end of the longest time period in geologic history.