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.
They are made up of a single cell. Organisms like the amoeba, Paramecium are single-celled organisms, they are the oldest forms of life, they existed about 3.8 million years ago. Bacteria, archaea, protozoa, unicellular algae and unicellular fungi are the main groups of unicellular organisms.