Precambrian Time
About the Precambrian Era The Precambrian era also called “The Age of Earth” Started about 4.6 billion years ago and ended about 523 million years ago. It was a period in earth history before the evolution of hard-bodied and complex organisms. Throughout the extent of both periods, dominant Precambrian and Vendian organisms were soft-bodied, simple, and entirely marine. The Climate based on physical and chemical principles, the Sun would have emitted less solar radiation 4.6 billion years ago and has increased ever since. During the later Precambrian, Earth's climate flip-flopped between very warm periods and very cold periods. The cold periods were so cold that extensive glaciers were found near the equator—a true "snowball" Earth! Major Changes to Shape and Location of the Continent The Earth's rocky outer crust solidified billions of years ago, soon after the Earth formed. This crust is not a solid shell; it is broken up into huge, thick plates that drift on top of the soft, underlying mantle. The plates are made of rock and drift all over the globe; they move both horizontally (sideways) and vertically (up and down). Over long periods of time, the plates also change in size as their margins are added to, crushed together, or pushed back into the Earth's mantle. These plates are from 50 to 250 miles (80 to 400 km) thick. Major Changes in the Landforms The most extensive early glaciation occurred 2.3 billion years ago during the early Proterozoic. It can be recognized from the rocks, and structures that the glaciers, and ice sheets left behind in Western Australia, Finland, Southern Africa, and North America. Shallow seas—like today's Caribbean—covered some of the early continents. During warm climates, mats, or mounds of algae called stromatolites grew in those shallow seas. The Precambrian used to be defined as the time from when the Earth's rocks formed until the earliest life forms evolved, but as the date of the earliest fossils gets earlier and earlier, this definition has also changed. Major Changes in the development of living things The first life forms on Earth were simple. single-celled life forms that evolved in the seas. The earliest-known fossils are of cyanobacteria-like organisms that are roughly 3.5 billion years old. The first billion years of life on Earth saw only these simple forms. Shark Bay, Australia is famous for its modern stromatolites. Billion-year-old stromatolites are found in Montana. Vendian marks the first appearance of a group of large fossils collectively known as the "Vendian biota" or "Ediacara fauna." Why the Precambrian Era Ended It's thought the final stages of Precambrian time were marked by a prolonged global ice age. This may have led to widespread extinctions, mirroring the bleak endings to the geologic periods that followed. |