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.
Unlike the other ancient eras, the Proterozoic Era contains good evidence of fossils which were mainly from archaeans and bacteria. This evidence is the proof that living organisms were in abundance in this era. The Era lasted from 2.5 billion years to 543 million years ago. Two major living organisms in existence of eukaryotic cells. At the mid of the Proterozoic Era there was an increase in the atmospheric oxygen.