The Precambrian Era - Article Example

The Precambrian Era INTRODUCTION Life must have had its origins as well as the world we live in right now. Our curiosity of these origins will then take us to the very first era in Earth history and that is the Precambrian Era. Everything must have begun during the Precambrian era – the formation of the universe, the heating up and cooling down of the Earth, the Ice Ages, formation of the first rocks, and finally the development of the first life forms. This paper will hopefully tackle all the events – both geological and biological – during this period in prehistory. Such valuable information will point out to us the ultimate origins not only of the plants and animals we see around us today or the mountains and seas where we often bask under the sun, but most especially – of the alternating hell-hot and extremely freezing temperatures that our ancient ancestors struggled to survive so that we may exist now. THE BEGINNING OF LIFE The Precambrian Era definitely began with the formation of the Earth, which was merely one point among the series of events after the formation of the Universe. The Beginning of the Universe, the Solar System and Life. According to the estimate of scientists, “the Universe [originated] between 10 and 20 billion years ago” and that currently the most accepted theory on this is the Big Bang theory, or “the idea that all matter in the Universe existed in a cosmic egg…that exploded, forming the Universe” (“The Precambrian: Life’s Genesis”). The formation of the solar system followed 5 billion years ago. Eventually, “the processes of radioactive decay and heat involved in the formation of the Earth [gradually] differentiated into a cooled outer crust [made up] of silicon, oxygen and other light elements” (“The Precambrian: Life’s Genesis”). It is also theorized that the “impact of asteroids and comets as well as the beginnings of volcanism[eventually led to the release of] water vapor, carbon dioxide, methane, ammonia and other gases [that eventually formed the] atmosphere” (“The Precambrian: Life’s Genesis”). It was shortly after this that life began. The building blocks of cells included not only gases like CO2 and NH3 but also small organic compounds which served as the first food and “were probably formed by the action of lightning, solar ultraviolet radiation, and other forms of energy on the gases of the secondary atmosphere.” (Margulis and Dolan 29) The Beginning of Life in the Sea. It is believed that life only began some 3.8 billion years ago, and that “the sea was the mother of all life…and remains so today” (“Precambrian Era Paleobiology”). The sea played a central role in the genesis and evolution of life and it is also central to any aspect of the geological history of the Earth. The sea is said to contain an “incomprehensible diversity of life…[from] microscopic life, including bacteria…and Archaeans…” (“Precambrian Era Paleobiology”) to macroscopic mammals that include the Blue Whale. Evidence points out to the sea as the true site of the origin of life. The so-called “ancient black smoker chimneys,” which was unearthed by scientists in a Chinese exploratory mine in 2007 “are nearly identical to the archaea and the bacteria-harboring structures” present on sea beds today (Mosher). The black smoker chimneys are like huge 50-foot-tall pillars of “1.43 billion-year-old fossils of deep-sea microbes” found by geologists and add to the growing amount of evidence that life originated “on the bottom of the ocean” (Mosher). A geologist at Saint Louis University named Timothy Kusky confirms that the ancient black smoker chimneys discovered in northern China “are remnants of the oldest living types of life forms on the planet” (Mosher). However it remains that the oldest evidence of life on Earth is still the stromatolites, or “3.5 billion-year-old, dome-shaped clumps of bacteria” (Mosher) discovered in Western Australia suggesting that life originated in the shallow seas. THE HADEAN TIME The Hadean Time encompassed the time from the Big Bang about 4.5 billion years ago until the formation of the Earth’s oldest rocks “through the cooling of the…molten Earth” at around 3.8 billion years ago (“Precambrian Era Paleobiology”). The Hadean time, with reference to “the Greek mythical Underworld Hades” (“Hadean Eon”) and with reference to the hell-like structure of Earth at that time, was the first and oldest Precambrian period and it was during this time that “the sun formed by gravitational compaction, and eventually reached temperature and pressure conditions [which were ideal] for nuclear fusion” and it was also during the Hadean time that “other particles coalesced under gravity to form continually growing planets” (“Precambrian Era Paleobiology”). Although it remains to this day uncertain whether life originated during the Hadean time, it remains certain that the ingredients needed for life began to emerge during that period of time and “if life did arise during the Hadean, it did so in a truly hellish environment.” (“Precambrian Era Paleobiology”) The Origin of the Term and Characteristics of the Period. The term “Hadean” was coined by the American geologist Preston Cloud, although another name for this Precambrian time was “Priscoan” (“Hadean Eon”). Prominent characteristics of the Hadean time included the absence of rocks on the Earth’s surface, which makes it differ from the next Precambrian period of time, namely the Archaean time. Other characteristics of the Hadean time included “fierce meteoritic bombardment” that added solid rock and water to early Earth, as well as the “formation of solid crust” and the “degassing and heat loss” as the “oceans began to accumulate.” (“Hadean Eon”) The Impact of the Heating Up of the Surface. Eventually the bombardment was reduced, “although volcanic activity continued at a very high level” and this added “water, carbon dioxide, and other gases to the new atmosphere.” This new atmosphere led to “a continuing gradual dehydration of the Earth’s mantle” due to the evaporation of water and when bodies of water were formed, “heat loss from the Earth now took place more through the oceans into the atmosphere rather than directly into the atmosphere itself.” (“Hadean Eon”) The Impact of the Cooling Down of the Surface. The cooling of the Earth and the seas as well brought down “temperatures in the seas…to a level at which the persistence of life in its earliest form was possible.” This eventually gave rise to the “development of self-replicating carbon-based structures” (“Hadean Eon”) which are believed to be hypothetical but which scientists consider to be the forerunner of the living things. It is also known that the advent of these biological processes also marked the beginning of the Archaean eon. Subdivisions of the Hadean Time. The Hadean time was further subdivided into four periods that are hardly indistinguishable from each other: the Cryptic period from 4567 to 4150 million years ago; the Basin Groups from 4150 to 3950 million years ago; the Nectarian period from 3950 to 3850 million years ago; and the Lower Imbrian from 3850 to 3800 million years ago. (“Hadean”) THE ARCHAEAN TIME General Features of the Archaean Time. The Archaean time began as soon as “rocks were beginning to form at the crust of the Earth” (“Precambrian Era Paleobiology”) and when “biological processes had begun” (“Hadean Eon”). These events began at around 3800 million years ago. The Archaean time persisted until around 2500 million years ago when the atmosphere finally cleared up due to “the steady buildup of oxygen” at the same time that “stable continents formed” and eukaryotic-celled animals [may have] evolved (“Precambrian Era Paleobiology”). It is said that since the atmosphere during the Archaean time was still “toxic to most extant life on [the] planet,” “life on Earth [somehow] made its [first] appearance in the seas” (“Precambrian Era Paleobiology”), particularly the Eubacteria, which are actually “single-celled prokaryotic organisms with no DNA-containing nucleus” and which are considered “ancestral to the Archaea.” The Archaea seems to have been the only organisms that “can exist in extremely hostile environments such as thermal vents and hypersaline water,” although “not all Archaeans are extremophiles.” (“Precambrian Era Paleobiology”) The First Life Forms. The 3,500 million-year-old bacterial microfossils discovered in Western Australia in the 1970s point to the possibility that “the earliest bacteria obtained their energy through chemosynthesis, [or the] ingestion of organic molecules” (“Precambrian Ear Paleobiology”). It is believed that these bacteria appeared “exactly like living blue-green algae,” or cyanobacteria. These blue green algae-like bacteria “formed extensive slimy carpets in shallow coastal waters…[and] a thin crust on land” for billions of years until the end of the Archaean time 2500 million years ago. The thin crust that these bacteria formed on land are called stromatolites, which are actually “accretionary growth structures produced by prokaryotes, possibly some Archaea, and [maybe even] primitive Eukaryotes.” (“Precambrian Era Paleobiology”) However, the evidence of stromatolitic structures made some experts formulate “an alternate hypothesis…that eukaryotes may have appeared in late Archaean time. The presence of “ancient shales…[with] microscopic traces of oil-containing sterols [that were found to have been formed] 2700 million years ago” is another evidence pointing out to this hypothesis “since eukaryotes are the only organisms on Earth that can make these molecules.” Furthermore, it was theorized that these early eukaryotes were “amoeba-like” (“Precambrian Era Paleobiology”). The ancient bacterial microfossils formed during the Archaean time “occur in marine rocks, such as limestones and sandstones, that formed in ancient oceans.” (“The Precambrian”) The Subdivisions of the Archaean Time. The Archaean time was made up of four consecutive periods: the Eoarchaean period from 3800 to 3600 million years ago when the very “first supercontinent Vaalbara formed” and when “the first species of stromatolites” and “the first unicellular organisms” first appeared; the Paleoarchaean period from 3600 to 3200 million years ago during which the Eubacteria and Archaea evolved; the Mesoarchaean period from 3200 to 2800 million years ago when nothing really significant happened; and lastly the Neoarchaean period from 2800 to 2500 million years ago when the first eukayotic-celled animals may have appeared (“Archaean”) THE PROTEROZOIC TIME The Beginning and End of the Proterozoic Time. The final division of the Precambrian era before the Cambrian was the Proterozoic eon, which extended from 2500 when the eukaryotic-celled animals started evolving to around 544 million years ago when the Tommotian fauna or “small shelly animals” (“Precambrian Era Paleobiology”) first appeared. These animals are believed to be the forerunners of the metazoans of the Cambrian age with hard exoskeletons. Subdivisions of the Proterozoic Time. The Proterozoic time is further divided into three relatively shorter periods: the Paleoproterozoic time from 2500 to 16oo million years ago when the oxygen atmosphere first formed and when the eukaryotes later originated; the Mesoproterozoic time from 1600 to 900 million years ago; and the Neoproterozoic time from 900 to 543 million years ago when the first and oldest animal fossils were first discovered. (“The Divisions”) Paleoproterozoic Time. The Paleoproterozoic time is further subdivided into Siderian period from 2500 to 2300 million years ago; the Rhyacian period from 2300 to 2050 million years ago; the Orosirian period from 2050 to 1800 million years ago; and the Statherian period from 1800 to 1600 million years ago (“Proterozoic”). During the Siderian Period, there was an “abundance of banded iron formations” which were formed as a result of “anaerobic algae [producing] waste oxygen” that forms magnetite, or iron oxide, when combined with iron. The Siderian period also marked the beginning of the “Huronian glaciation.” (“Proterozoic”). The Rhyacian period was marked by the formation of “the Bushveld Complex and other similar intrusions.” The Orosirian period was the true beginning of the oxygen-rich atmosphere due to photosynthesis and the action of cyanobacteria. Lastly, the Statherian period was the exact time that “the first complex single-celled life appeared” as well as the formation of “the supercontinent Columbia” during its beginning. (“Proterozoic”) Mesoproterozoic Time. The 600-year Mesoproterozoic time was made up of three periods: The Calymmian period from 1600 to 1400 million years ago; the Ectasian period from 1400 to 1200 million years ago; and the Stenian period from 1200 to 1000 million years ago. The Calymmian period was the time when the existing platform covers expanded also the time when “the supercontinent Columbia broke up.” The Ectasian period was characterized by the “continued expansion of platform covers.” Lastly, the Stenian period was marked by the formation of “narrow polymetamorphic belts” and the assembly of “the supercontinent Rodinia.” (“Proterozoic”) Neoproterozoic Time. The Neoproterozoic time was also made up of three relatively shorter geologic divisions: the Tonian period from 1000 to 850 million years ago when “the supercontinent Rodinia started to break up” and when the forerunners of the fungi and green algae first appeared; the Cryogenian period from 850 to 630 million years ago when the Sturtian and Marinoan glaciations started, and when glacial deposits were at its maximum making “the Earth [suffer] the most severe ice ages in history…[resulting in] deeply-frozen planetary oceans”; and lastly the Ediacaran, or Vendian, period from 630 to 542 or 544 million years ago when the first primitive Ediacaran fauna first appeared. (“Proterozoic”) Diversity and Endosymbiosis. On the whole, the Proterozoic time was an explosion of diversity among animals and plants due to “the intense energy density of oxygen-burning aerobic metabolism of Eukaryotes.” Moreover, it was during this time that some of the living cyanobacteria transformed into the chloroplasts of photosynthetic plants. The cellular organelle mitochondria in animals, which serve as the center of aerobic energy production, is also said to have “evolved from aerobic bacteria.” This and the cyanobacteria that transformed into chloroplasts supported the “theory of endosymbiosis” (“Precambrian Era Paleobiology”), which occurred only during the Proterozoic time. Aside from endosymbiotic-based metabolism, other notable developments on eukaryotes that occurred in the Proterozoic time was sexual reproduction, survival and adaptation mechanisms, and “favorable mutations [that persisted] and [amplified]…a population’s genome.” Finally this was also the beginning of the evolution of “multi-celled, soft-bodied marine organisms [known as] metazoans.” (“Precambrian Era Paleobiology”) OTHER KEY FEATURES OF THE PRECAMBRIAN ERA The Ice Age. The Cryogenian period of the Proterozoic eon is known as the time that the Ice Age, one of the most extreme climate changes in the history of the Earth, occurred. That was around 635 million years ago (Hoffman). In fact, there were “at least three ice ages during that ancient time” (Trulove). No one exactly knew what caused the Ice Age although a number of people think that it was due to the “tilting of the Earth” for 2500 million years ago, “the Earth had a much larger tilt [of around 54 degrees] than today [which is 23.5 degrees].” (Chris) The Cryogenian Ice Ages. On the subject of the three glaciations during the Cryogenian period, a group of American and Chinese geologists studied and investigated glacial deposits from the Cryogenian period and after several years, they have hypothesized “that the earth was covered with ice and the oceans frozen to a depth of one or two kilometers” (Trulove) compared to its current position. This scenario is called “Snowball Earth.” This theory is said to have profound explanations and one of which is that “there [was] no communication between the atmosphere and the ocean [which means that] the deep ocean [quickly became] free of oxygen because light [was] not able to penetrate the ice to fuel algae [and] above the ice there [was] little rain or snow because there [was] little evaporation, [thus] many organisms that lived in milder conditions [became] instinct.” (Trulove) In southern China, it was discovered that “there are at least three [consecutive] levels of glacial deposits” (Trulove). These glacial deposits contained mainly the element zircon in the midst of the thin layer of volcanic ash. The stable zircon minerals were subjected to radioisotope measurements and results pointed out to an existence 663 million years ago. In southern Australia and several other places, “there is evidence for only two Cryogenian glaciations [namely] the Sturtian [which] occurred about 720 million years ago and the…Marinoan [which] occurred 630 million years ago” (Trulove). Gaskiers Ice Age. It is however interesting to note that “in Newfoundland and Cape Cod, Massachusetts, there is evidence for a much younger glaciation, known as the Gaskiers glaciation” (Trulove) during the Ediacaran period, the last period of the Precambrian Era. This is said to have taken place 20,000 years ago. Thus there is a current total of “at least three Cryogenic ice ages [namely] the Sturtian, Marinoan, and Gaskiers.” (Trulove) The First Ice Age. It should however be known and noted that a less severe Ice Age occurred in the Paleoproterozoic time, specifically during the Siderian period around 2500 million years ago. This is known as the “Huronian Ice Age” or Huronian glaciation. The Ice Age during the Cryogenian period, however, was the “most severe.” (Chris) The Second Ice Age. There was also considerable evidence which points out to the existence of yet another glaciation, this time in Africa, and it is known as the Makganyene glaciation, which “occurred near the end of the older period,” or Paleoproterozoic time. This Ice Age “ended with the deposition of iron-formation and the largest sedimentary manganese deposit on record.” (Hoffman) Effects of the Ice Age on Biological Development. It is also interesting to know that the Cryogenian Ice Ages had a biological effect on the life forms during that time for after such a geologic event, “the microbes and bacteria that survived the long chill developed into something more” giving rise to new life forms that signaled the beginning of the “Cambrian Explosion.” (Chris) Ancient Continents. The Precambrian Era was also characterized by the formation of ancient continents and supercontinents. Vaalbara. The first theorized supercontinent of the world was the Vaalbara. This supercontinent was said to have been formed around 3600 to 3300 million years ago during the Paleoarchaean period of the Archaean eon (“Formation and History”) although there are some claims that it must have formed during the earlier Eoarchaean period from 3800 to 3600 million years ago (“Proterozoic”). Columbia. Another one of these continents was Columbia, which is regarded as “the first real supercontinent” (“Formation and History”) and was formed at around 2000 to 1800 million years ago during the Orosirian period of the Paleoproterozoic time, although some experts say it formed in the Statherian period 1800 to 1600 million years ago (“Proterozoic”). This supercontinent “started fragmenting between 1600 and 1400 million years ago” (“Formation and History”) during the Calymmian period of the Mesoproterozoic time. Rodinia. The ancient continent Rodinia was formed from “fragments of Columbia that re-assembled around 1100 to 1000 million years ago” (“Formation and History”). Rodinia mostly occupied the south of the equator and the continent was “surrounded by a super-ocean named Mirovia” (“Formation and History”). The continent started to break up between 800 to 750 million years ago during the Cryogenian period of the Neoproterozoic time. Rodinia was considered “the first continent” and “contained [ancient] North America, South America, Australia and Antarctica.” (“The Precambrian: Setting”) Other Continents. Other less prominent ancient continents include the Arctica, formed around 2500 million years ago and now makes up Canada and Greenland; the Atlantica, formed 2000 million years ago and now makes up West and Central Africa and North Eastern South America; and Nena, formed around 1800 million years ago and which makes up present Northern Europe and North America, for which “Nena” stands for. (“Formation and History”) Precambrian Rocks. Precambrian rocks emerged to the surface during the beginning of the Archaean eon from 3800 to 2500 million years ago. The rocks around this time were classified as “microtektites, pseudotachylites, and spherules.” (Eriksson et al. 52) Tektites. Tektites were made up of “impact melt that may have travelled between 20 and 80 km into the stratosphere.” Some were made up of “perfectly clear, nearly pure silicate glass” and possessed “teardrop shapes and dumbbell forms.” (Eriksson et al. 52) Pseudotachylites. Pseudotachylites were “fault rocks of dark colors and glassy appearance similar to basalt.” (Eriksson et al. 53) Spherules. Spherules contained “randomly oriented crystal aggregates” with varying colors and surface textures. (Eriksson et al. 54) Most Precambrian rocks were volcanic in origin, formed from sediments, or a result of the breakdown of impact rocks coming from space. CONCLUSION The Precambrian era was made up of three relatively shorter but actually very long geologic eras: the Hadean time where the Earth was still being formed; the Archaean time which marked the beginning of primitive life forms; and the longest of all, the Proterozoic time where various events happened – the formation of the supercontinents, the Ice Ages and the first true bacteria and cells. The Precambrian era may still be an unexplored area of paleontological knowledge but it certainly explains the origin of all the geologic phenomena and the life processes that followed it. Works Cited “Archaean.” Precambrian. 6 Apr 2010. Palaeos.org. 15 Apr 2010. Chris. “Mother Earth: How Ice Shaped the Face of the Planet.” Ecology. n.d. Environmental Graffiti. 17 Apr 2010. Eriksson, P. G., Altermann, W., Nelson, D. R., Mueller. W. U. & Catuneanu, O (Eds.). The Precambrian Earth: Tempos and Events. San Diego, CA:  Elsevier B. 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Cartage.org. 16 Apr 2010. “The Precambrian: Setting the Stage for Complex Life.” Geologic Time. n.d. Fossil-facts-and-finds.com. 16 Apr 2010. Trulove, Susan. “New Evidence Supports Three Major Glaciation Events in the Past.” EurekAlert. 19 Apr 2004. EurekAlert. 16 Apr 2010. Read More