Precambrian era how long did it last

Precambrian , period of time extending from about 4. What percentage of the timeline falls in the Precambrian era? What was the shortest era? The Quaternary spans from 2. How did Earth's atmosphere change during Precambrian time? Some three billion years ago, the Earth's atmosphere was virtually devoid of oxygen.

At about 2. Levels of the gas gradually climbed, reaching about one percent around two billion years ago. What did the Earth look like during the Precambrian era? During this era the surface of the Earth was like popular visions about Hades: oceans of liquid rock, boiling sulfur, and impact craters everywhere!

Precambrian time covers the vast bulk of the Earth's history, starting with the planet's creation about 4. The Precambrian is the earliest of the geologic ages , which are marked by different layers of sedimentary rock. Laid down over millions of years, these rock layers contain a permanent record of the Earth's past, including the fossilized remains of plants and animals buried when the sediments were formed.

The Earth was already more than million years old when life began. The planet had cooled down from its original molten state, developing a solid crust and oceans created from water vapor in the atmosphere.

Many scientists think these primordial seas gave rise to life, with hot, mineral-rich volcanic vents acting as catalysts for chemical reactions across the surface of tiny water bubbles, which led to the first cell membranes. Other bubbles are thought to have formed self-replicating substances by attracting chemicals from around them. Over time the two combined to produce energy-using, living cells. The earliest living organisms were microscopic bacteria, which show up in the fossil record as early as 3.

As their numbers multiplied and supplies of their chemical fuel were eaten up, bacteria sought out an alternative energy source. New varieties began to harness the power of the sun through a biochemical process known as photosynthesis—a move that would ultimately lead to simple plants and which opened the planet up to animal life.

Some three billion years ago, the Earth's atmosphere was virtually devoid of oxygen. At about 2. Levels of the gas gradually climbed, reaching about one percent around two billion years ago. About million years ago, oxygen levels reached about 21 percent and began to breathe life into more complex organisms. The oxygen-rich ozone layer was also established, shielding the Earth's surface from harmful solar radiation. It is generally accepted that different types of prokaryotic organisms formed symbiotic relationships.

Microfossils of these early cells are called Acritarchs. About 1. Photosynthesis began to add oxygen to the atmosphere, putting pressure on organisms adapted to the reduction atmosphere of the early Earth. After a brief ice age in the mid-Proterozoic, organisms underwent rapid differentiation. The Ediacaran Period , the last of the Proterozoic Era, saw the first multicellular organisms. Autotrophs and soft-bodied heterotrophs filled the continental shelf regions around Rodinia.

Many were Cnidarians similar to small jellyfish with radial body symmetry and specialized cells to sting prey and convey it into the body cavity. High mountain ranges and plateaus were built or pushed up above the level of the ocean until finally the continents settled to the forms of continental blocks our geographies show today.

However, the Precambrian oceans did not settle in the basins we know, but covered much of the continents with shallow seas in which the story of a billion years of earth history was to be recorded. The continental shelves are, even today, covered by shallow seas and there the geologic history of today is being recorded. What are these records made in the shallow seas these tablets of time on which the story of ages is told?

When the first igneous rock cracked, when the first drop of water moved, the record began. When the atmosphere cooled and frost arrived the recording became more rapid. When plant and animal life became abundant the record became complicated. Changes of temperature caused the granitic rocks to flake off at the surface, gravity and moving waters carried the loosened rocks down the slopes, rolled them together, broke them into smaller and smaller particles, carried them to the sea where they became sediments that muddied the seawater.

Some of the sediments were dissolved in the water, and as the process kept on through the ages the seas became salty. The sediments, sorted by waves and currents of the first oceans, settled to the bottom of the seas and were spread out on the sea floor. In the course of a long time, as layer upon layer of sediments were piled one on another, they were compressed, cemented, and consolidated into rock which we call sedimentary. Each layer or bed is a stratum; layered or bedded rock is said to be stratified.

Various minerals in the ancient igneous rocks were made over into different sediments. The hard minerals like quartz collected together as sand, and being heavy, were not carried so far out to sea.

They built up coarse and fine rocks which we call sandstones. Other minerals were broken up into fine clay and silt muds that were carried far from shore but eventually settled on the sea floor and compacted to a rock we call shale. Some of the minerals disintegrated to form lime, or calcium carbonate. As the igneous rocks were eroded some minerals dissolved and were carried to the sea in solution; there certain chemical reactions caused the lime to be precipitated and in places to build up great thicknesses of lime mud that eventually solidified into a rock known as limestone.

Other chemical reactions caused iron minerals to be formed which in turn settled to the bottom of shallow seas, and later in the geological history gypsum and salt crystallized out of the sea water to form great beds of gypsum and rock salt. Proterozoic Proterozoic "Early Life" Era. Well, here we are about million years ago, near the end of the longest time period in geologic history. It began about two billion years after the formation of the earth and lasted about another two billion years!

So what has happened in all that time? There is a lot more land to be seen. In fact, there are two supercontinents, one visible across the equator on this side of the earth and another one on the other side.

These huge masses of land formed by collisions of the many, many islands made by volcanoes during the Archean and most of the Proterozoic eras.

The earth's interior has cooled some more, and there are fewer volcanoes than in the Archean. Even though the movements of the earth's surface we call Plate Tectonics are still very fast and continental collisions are frequent every few hundred million years or so!

In fact, geologists date the beginning of the Proterozoic Era by the age of the oldest continental rocks that have not been reheated or chemically altered. Life has not changed much during the last two billion years, but the few changes are significant. Life is still found only in the ocean, but somewhere around 1. Another important change is about to happen: true multi-celled life is about to appear, some 30 million years before the end of the Proterozoic.