-Las caracteristicas Geodinamicas comienzan a ser mas pasivas. -Primero formacones cristalinas en continentes y formaciones basalticas en. Convert documents to beautiful publications and share them worldwide. Title: Conclusiones Eon Proterozoico, Author: wilo bope, Length: 7 pages, Published. First, a few words about the Precambrian, an informal name for the vast expanse of time prior to the Phanerozoic Eon (which includes the Paleozoic, Mesozoic.

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First, a few words about the Precambrian, an informal name for the vast expanse of time prior to the Phanerozoic Eon which includes the PaleozoicMesozoicand Cenozoic Eras. It then took nearly four thousand million years before the first animals would leave their traces on the planet. This span of time makes up roughly seven-eighths of the Earth’s history. During the Precambrian, the proteroaoico important events in biological history took place.

The Precambrian is divided into three eoon. From youngest to oldest, they are: The period of Earth’s history that began 2. Also coming from this time are the first abundant fossils of living organisms, mostly bacteria and archaeans, but by about 1.

Primicias Arrecifes » Eón Proterozoico

With the beginning of the Mesoproterozoic comes the first evidence of oxygen build-up in the atmosphere. This global catastrophe spelled doom for many bacterial groups, but made possible the explosion of eukaryotic forms. These included multicellular algae, and toward the end of the Proterozoic, the first animals.

The first traces of life appear nearly 3. However, clearly identifiable fossils remain rare until the late Archean, when stromatolites, layered mounds produced by the growth of microbial mats, become common in protwrozoico rock record. Stromatolite diversity increased through most of the Proterozoic.

Pproterozoico about one proerozoico years ago, they flourished in shallow waters throughout the world. Their importance for understanding Proterozoic life is tremendous; stromatolites that have been silicified forming a type of rock known as stromatolitic chert often preserve exquisite microfossils of the microbes that made them see two photos, below left.


From left, 1 A sample of stromatolitic chert from the Bitter Springs Formation of central Australia, about million years old. Note the typical fine banding patterns. This specimen, from the White Sea region of Russia, is about 1. These Ediacaran organisms have a bulb-shaped or disc-shaped “holdfast” which was attached to the sea floor, and a leaf-shaped main body that probably was held up in the water column.

Stromatolites began to decline in abundance and diversity about million years ago. A popular theory for their decline though certainly not the only possible explanation is that herbivorous eukaryotes, perhaps including the first animals, evolved at about this time and began feeding extensively ;roterozoico growing stromatolites.

Stromatolites are rare fossils after about million years ago. Today, they are found only in restricted habitats with low levels of grazing, such as the shallow, saline waters of Shark Bay, Australia. The oldest fossil that may represent a macroscopic organism is about 2. Several types of fossil that appear to represent simple multicellular forms of life are found by the end of the Paleoproterozoic.

These fossils, known as carbon films, are just that: Some resemble seaweeds and may represent eukaryotic algae; we know from independent evidence that red algae and green algae appeared in the Proterozoic, probably over one billion years ago.

There are tantalizing hints from trace fossils and molecular biology that animals may have appeared as much as one billion years ago. However, the oldest relatively non-controversial, well-studied animal fossils appear in the last hundred million years of the Proterozoic, just before the Cambrian radiation of taxa. The time from million years ago to million years ago, known as the Ediacaran Period sometimes called the Vendiansaw the origin and first diversification of soft-bodied organisms see proteorzoico photos, above right.



The period and the fauna are named after the Ediacara Hills of southern Australia, where the first abundant and diverse fossils of this kind were found. Ancient global pollution The first “pollution crisis” hit the Earth about 2. It may seem strange to call this a “pollution crisis,” since most of the organisms that we are familiar with not only tolerate but require oxygen to live.

However, oxygen is a powerful degrader of organic compounds. Even today, many bacteria and protists are proetrozoico by oxygen. Organisms had to evolve biochemical methods for rendering oxygen proterozooco one of these methods, oxidative respiration, had the advantage of producing large amounts of proterozooco for the cell, and is now found in most eukaryotes. Where was the oxygen coming from?

Cyanobacteria proteozoico, photosynthetic organisms that produce oxygen as a byproduct, had first appeared 3. Their photosynthetic activity was primarily responsible for the rise in atmospheric oxygen. The oldest known eukaryotic fossils come from this Late Proterozoic dolomite in central Australia. Fossils of some of the oldest known animals were discovered at this Australian locality in Mysterious fossils from the coast of Newfoundland. The oldest sedimentary rocks in this Southern California region are 1.

See the world and its fossils with UCMP’s field notes. Geologic time scale First, a few words about the Precambrian, prpterozoico informal name for the vast expanse of time prior to the Phanerozoic Eon which includes the PaleozoicMesozoicand Cenozoic Eras.

The Proterozoic Eon The period of Earth’s history that began 2. Life The first traces of life appear nearly 3.