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.
Earthâs History 371 Early Paleozoic Life Life in early Paleozoic time wasrestricted to the seas. Ve rtebrates had not yet evolved,so life consistedof several invertebrate groups. The Cambrian period was the goldenage of trilobites. More than 600 types of these mud-burrowing scav-engers flourished worldwide.arly Paleozoic History During the Cambrian,Ordovician,and Silurian periods,the vast southern continent of Gondwana encom-passed ï¬ve continents (South America, Africa, Australia, Antarctica,India, and perhaps China). North America and several other landmasses were not part ofGondwana.