What makes up the precambrian era

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. The first multicelled animals appeared in the fossil record almost million years ago.

Known as the Ediacarans , these bizarre creatures bore little resemblance to modern life-forms. By the end of the Archean, the ocean floor was covered in a living mat of bacterial life.

The Proterozoic Eon is also called the Cryptozoic "age of hidden life". About 2. 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. Over the four billion years of the Precambrian the Earth's surface features changed vastly. Beginning as glowing ball of molten rock, Earth cooled to the pre-plate tectonic realm of the Archean. This was followed by two billion years of plate tectonics during the Proterozoic. These maps of major tectonic elements plates, oceans, ridges, subduction zones, mountain belts are used with permission from Dr.

Ron Blakey at Northern Arizona University. The positions of mid-ocean ridges before Ma are speculative. Explanation of map symbols. Cambrian Period. The Precambrian begins with the formation of the Solar System 4. Over this immense time span the Solar System condensed from a cloud of dust and gas, the Earth was violently accreted from the collisions of smaller bodies, organic molecules were formed, and life originated from the resulting soup.

In a very short period geologically speaking the progenitor cell of all modern life evolved and then diverged into the three great domains of modern life on Earth: the bacteria, the archea bacteria-like organisms often living in extreme environments , and the eukarya protists, fungi, plants and animals. Over the next three billion years these three domains of life diversified into the incredible variety of organisms appearing in the "Cambrian explosion.

Essentially all of the great inventions of life were made during the Precambrian, including the ability to capture the energy of sunlight, the creation of an oxygen atmosphere, metabolism, the vast repertoire of biosynthetic products, sexual reproduction, the ability to detect light, communication by chemical signals, the metazoan body plans, and vascular plants all appear during this time.

In fact the marvelous diversity of living organisms seen in the past five hundred million years is essentially just variations on themes already invented - refinements if you will of the inventions of the Precambrian.

For those who wish to learn more about the Precambrian a bibliography is available via this link. Most meteorites were formed within about million years of the formation of the solar system. They are the oldest objects on Earth and they tell us about the conditions in the solar system when the Earth was just being condensed out of the solar nebula.

Most meteorites are fragments of asteroids resulting from collisions in the asteroid belt. The most primitive meteorites are undifferentiated, that is they have never been melted and their component materials allowed to separate under gravitational attraction or recombine chemically.

Such meteorites may have formed on the surface of an asteroid or been part of an asteroid too small to melt during its accretion. Meteorites originating from the interiors of large asteroids, on the other hand show varying degrees of differentiation, depending on the size of the asteroid, and thus how long it may have remained in a molten state.

One of the great stories of the Precambrian is the evolution of an oxygen atmosphere. Oxygen in the atmosphere not only resulted in one of the greatest ecological crises in Earth's history, it also was a necessary precursor to the evolution of multicellular animals metazoans.

So when did life first begin producing oxygen in significant amounts? The earliest records of cells are microfossils of cyanobacteria from about 3. Since all modern cyanobacteria produce oxygen by photosynthesis it is widely thought that oxygen production must date back to at least this time. Mysteriously, the geological evidence banded iron formation, sulfide vs. A variety of explanations have been offered, for example, the oxygen may have been consumed by early geological processes.

But like much in the Precambrian, the true cause remains unknown. A variety of specimens in our collection document the change to an oxygen atmosphere.

Though more complex in reality, the reaction can be symbolized as:. This group includes the Wawa granite-greenstone subprovince, the Quetico subprovince metamorphosed sedimentary rocks and gneiss derived from them , and the Wabigoon granite-greenstone terrane Fig.

The Wawa and Wabigoon subprovinces originally were parts of volcanic chains that were later deformed and intruded by granitic rocks; the Quetico subprovince was likely a large sedimentary basin on or between those volcanic arcs.

Greenstone a dark greenish-gray, fine-grained, weakly metamorphosed basalt; Fig. As these volcanic chains collided they were intruded by large amounts of granite and related coarse-grained rocks that crystallized at depth from the molten state, but are now revealed at the surface by deep erosion over time. The granites welded the greenstone belts together to form an Archean continent.

The Neoarchean rocks, collectively, are called the greenstone-granite terrane. The Ely greenstone is a well-known example of Neoarchean rock. Photo courtesy of James St. Rocks of the gneiss terrane are quarried in the Minnesota River valley for use as building stone and are also crushed for road construction and railroad ballast, among other things.

Rocks of the greenstone-granite terrane are also quarried for stone, and have been extensively explored for various metals including gold, copper, zinc, lead, and iron, but no deposits worth mining have been found, except for the now-closed iron mines near Ely and Soudan. Proterozoic rocks form two belts of very different ages and geologic histories in the eastern and central parts of Minnesota Fig. The older belt Paleoproterozoic crops out from St.

The younger belt Mesoproterozoic runs along the shore of Lake Superior and continues south along the Minnesota—Wisconsin border and southwest to Kansas. The southern part of the Paleoproterozoic terrane—approximately south of a line that runs west from Jay Cooke State Park Fig.

These were intruded later by several large granitic intrusions, emplaced between 1, and 1, Ma, which collectively form an amalgamation referred to as the East-Central Minnesota batholith Fig.