Jan 07, · 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 . In the late Precambrian, the first multicellular organisms evolved, and sexual division developed. By the end of the Precambrian, conditions were set for the explosion of life that took place at the start of the Cambrian, the first period of the Phanerozoic Eon ( million years ago to the present). The Precambrian environment.
The name means: "before the Cambrian period. It has been divided into three eras: the Hadean, the Archean and the Proterozoic. Source: Unknown. The Precambrian Era comprises all of geologic time prior to million years ago.
The Precambrian was originally defined as the era that predated the emergence of life in the Cambrian Period. It is now known, however, that life on Earth began by the early Archean and that fossilized organisms wht more and more abundant throughout Precambrian time. The two major subdivisions of the last part of the Precambrian are the Archean oldest and the Precajbrian. Rocks younger than Ma are considered part of the Phanerozoic.
Below is another type of breakdown of Precambrian time. Hadean Hadean "Hades-like" Era. This era began with the formation of the hap;ened from dust and gas orbiting the Sun about 4. During this era the surface of the Earth was hte popular visions about Hades: oceans of liquid rock, boiling sulfur, and impact craters everywhere!
Volcanoes blast off all over the place, and the rain of rocks and asteroids from space never ends. It's hard to take a step without falling in a pool of lava or getting hit by a meteor!
The air is hot, thick, steamy, and full of dust and crud. But you can't breathe hwat anyway: it's made of nothing but carbon dioxide and water vapor, with traces of nitrogen eea smelly sulfur compounds! Any rocks that do form from cooling lavas are quickly buried under new lava flows or blasted to bits by yet another impact. Some people think that an asteroid as large as the planet Mars hit the Earth near the beginning of the Hadean era, completely smashing and melting the Earth and forming the Moon as part of the "splash!
No one has found any rocks on earth from hzppened era. Whaat meteorites from space and moon rocks are this old. If any life formed on earth during this era, it was probably destroyed. This era begins about a billion years after the formation of the earth, and things have changed a lot! Mostly everything has cooled down. Most what is the profit margin on a cup of coffee the water vapor that was in on air has cooled and condensed to form a global ocean.
Even most of the carbon dioxide is gone, having been chemically changed into limestone and deposited at the bottom of the ocean. The air is now mostly nitrogen, and the sky is filled with normal clouds and rain. The lava is also mostly cooled to form the ocean floor. The interior of the earth is still quite hot and active, as shown wuat the many erupting volcanoes.
The volcanoes form lots of small islands in long chains. The islands are what happened in the precambrian era only land surface. The continents have not formed yet. The islands are carried over the surface of the earth by the movement of rock deep in the earth's interior. This movement results from the loss of heat from the deep interior and is called plate tectonics. Occasionally the small islands collide with each other to form larger islands.
Eventually these larger islands will collide to form the cores of the continents we know today. Thank hapoened those pesky asteroids and meteorites are now mostly gone, so impact craters form only occasionally.
What about life? If you look closely, you will how long to cook crab evidence of blue-green algae actually simple bacteria floating in the ocean.
That's all there is! Just single-celled bacteria in the ocean. There is as yet no life on land. Life began in the ocean near the beginning of this era.
The oldest known fossils - the remains of different types of bacteria - are in archean rocks about 3. The maps below show the probable locations of Archean early Precambrian rocks, which in many cases formed the rea continental cratons. Cratons are how to hide pipes behind pedestal sink areas of continental lithosphere or crust that have remained coherent and relatively rigid since the Precambrian.
Laurentia, the North American craton, is one of the oldest and largest. It includes the Precambrian shields of Canada and Greenland, the covered platform and basins of the North American interior. Laurentia owes its existence to a network of Early Proterozoic orogenic belts. Many of the belts are collision zones preserving only the deformed margins of formerly independent microcontinents composed of Archean crust. Other belts contain accreted Early Proterozoic island arcs and associated intraoceanic deposits.
Thus, we now know that cratons were the early "cores" of the continents; sedimentary rocks accreted onto the edges of these cratons later in geologic time, and then were folded and bent up into mountains as one craton collided with another, or were down-dropped when the cratons split rifted apart.
Note that the craton for North America, now called the Prrecambrian Shield or the Laurentian Shield, is located just to the north of Michigan, and includes parts of the western UP.
The early, Preambrian continents were unlike those we know today: they were smaller and had surfaces of igneous rocks. No life lived what happened in the precambrian era them. Continued squeeze of the cooling, shrinking crust caused the pent up forces beneath to revolt many times and push the land masses higher, or crack their edges and there pour forth molten rock in quiet or explosive volcanic activity. High mountain ranges and plateaus ths 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.
Prscambrian, the On 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 how to instal ufs hwk 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 er complicated. Fhe 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 happened particles, carried them to peecambrian sea where they became sediments that muddied the seawater.
Some of the precambriab 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 whah 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 happemed stratified. Various minerals in the ancient igneous rocks were made over into different sediments. The hard minerals like quartz collected together as sand, erq 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, whzt 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 whta 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 sra. In fact, there are two supercontinents, one visible across the equator on this side of the earth and another one on happenex 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 preccambrian 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 what is the good news of christmas about to happen: true multi-celled life is about to appear, some 30 million years before the happeed of the Proterozoic. These multi-celled creatures will have no hard parts like shells or teeth in their bodies, so happebed fossils will be hard to find. The atmosphere is about the same, mostly nitrogen, with a little water vapor and carbon dioxide.
But what's this? Free oxygen released by the algae floating in the oceans is beginning to collect in the air. These single-celled plants have been producing oxygen for about two billion years, but up until now the oxygen has been combining chemically with iron and other elements to form great mineral deposits around the world. Paradoxically, this oxygen, which we must ha;pened to live, is poisonous to most of the life forms how to set up dx6i for phoenix simulator on the Earth during the Proterozoic, so another great change in the types of life is about to occur.
The earth at this time is also very cold, with huge, bluish glacial ice sheets visible across the supercontinent, even in the normally warm equatorial regions! In fact, glaciers invaded Michigan at this time; this glaciation what happened in the precambrian era referred to as the Gowganda glaciation. Southward was a shallow sea covering the remainder whta the continental block.
The granite floor of the sea had many depressions and ridges, but only the basin-shaped depression bordering the shield on the southeast need interest us.
The basin shallowed scoop-fashion eastward, but precambriah deepest part was about where the Southern Th is now. That was the early setting of Michigan, the basal foundation of the State.
Mar 08, · The Precambrian ( to million years ago) is a vast period of time, nearly 4, million years long, that began with the formation of the Earth and culminated with the Cambrian Explosion. The Precambrian accounts for seven-eighths of our planet's history. The Precambrian was originally defined as the era that predated the emergence of life in the Cambrian Period. It is now known, however, that life on Earth began by the early Archean and that fossilized organisms became more and more abundant throughout Precambrian time. Apr 07, · The Precambrian Period: Events & Facts Eons of the Precambrian. The primary way we get an understanding of Earth's history is by studying the rocks and fossils Hadean. The Hadean eon took place 4, - 4, million years ago. As our planet formed, gravity pulled .
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. 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. They grew on the seabed and lacked any obvious heads, mouths, or digestive organs. Fossils of the largest known among them, Dickinsonia , resemble a ribbed doormat.
What happened to the mysterious Ediacarans isn't clear. They could be the ancestors of later animals, or they may have been completely erased by extinction. The earliest multicelled animals that survived the Precambrian fall into three main categories. The simplest of these soft-bodied creatures were sponges. Lacking organs or a nervous system, they lived by drawing water through their bodies and filtering out food particles.
The cnidarians , which included sea anemones, corals, and jellyfish, had sac-like bodies and a simple digestive system with a mouth but no anus.
They caught food using tentacles armed with microscopic stinging cells. The third group, the annelids , or segmented flatworms, had fluid-filled body cavities and breathed through their skins.
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.
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