Precambrian is the oldest part of the history of the Earth, founded before the present Phanerozoic Eon. It was called the Precambrian, because it came before Cambrian, the first period of Phanerozoic eon after Cambria, the Latin name in Wales where the rocks were studied for the first time. Precambrian constitutes 88% of the geological time in the world.
Most sources list the this as an era; others just refer to it as “Precambrian Time.” In other words, like many other parts of the geologic time scale, there are disagreements among charts.
Most charts do agree that the time of this is broken down into several other divisions. In some countries, it is divided into the following: Hadean (after Hades, with no rock record so far discovered); Archean (meaning ancient-it contains little evidence of life, and the Earth conditions were very dissimilar to today’s planet); and Proterozoic (meaning early life-a time when multicellular organisms started to appear as fossils and conditions on Earth were becoming more similar to today’s). Other charts divide into the Priscoan (oldest), Archean, and Proterozoic, while still other scales mention merely the Archean and Proterozoic.
But there is one thing everyone seems to agree upon so far: The Precambrian included about 80 percent of Earth’s history, lasting from about 4.56 billion years ago to about 545 million years ago. During this time, the most significant Earth events occurred, including the formation of the Earth, the beginnings of life, the first movement of tectonic plates, the formation of eukaryotic cells, and the enrichment of the atmosphere with oxygen. Just before the Precambrian ended, multicellular organisms evolved, including those that eventually produced the first plants and animals.
