Friday, February 15, 2013

Precambrian Eon

Is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Super Eon divided into several eons of the geologic time scale.It spans from the formation of Earth about 4570 Ma (million years) ago to the beginning of the Cambrian Period.

The Precambrian Supereon is divided into three Precambrian eons: the Hadean (4500-3950 Ma), Archean (4000-2500 Ma) and Proterozoic (2500-541.0 ± 1.0 Ma).

Hadean Eon
3800 Ma and earlier.

4600 Ma > The planet Earth forms from the accretion disc revolving around the young Sun; complex organic molecules necessary for life may have formed in the protoplanetary disk of dust grains surrounding the Sun before the formation of the Earth.
4500 Ma > According to the giant impact hypothesis the moon is formed when the planet Earth and the planet Theia collide, sending a very large number of moonlets into orbit around the young Earth which eventually coalesce to form the Moon. The gravitational pull of the new Moon stabilises the Earth's fluctuating axis of rotation and sets up the conditions in which life formed.
4100 Ma > The surface of the Earth cools enough for the crust to solidify. The atmosphere and the oceans form. PAH infall, and iron sulfide synthesis along deep ocean platelet boundaries, may have led to the RNA world of competing organic compounds.
4500-3500 Ma > The earliest life appears, possibly at Alkaline vents with the creation of the Last Universal Common Ancestor, possibly derived from self-reproducing RNA molecules. The replication of these organisms requires resources like energy, space, and smaller building blocks, which soon become limited, resulting in competition, with natural selection favouring those molecules which are more efficient at replication. DNA molecules then take over as the main replicators and these archaic genomes soon develop inside enclosing membranes which provide a stable physical and chemical environment conducive to their replication: proto-cells.
4000 Ma > Formation of Greenstone belt of the Acasta gneisses of the Great Slave Region, in Canada, the oldest rock belt in the world.
3900 Ma > Late Heavy Bombardment: peak rate of impact events upon the inner planets by meteoroids. This constant disturbance may have obliterated any life that had evolved to that point, or possibly not, as some early microbes could have survived in hydrothermal vents below the Earth's surface; or life might have been transported to Earth by a meteoroid.
3900-2500 Ma > Cells resembling prokaryotes appear. These first organisms are chemoautotrophs: they use carbon dioxide as a carbon source and oxidize inorganic materials to extract energy. Later, prokaryotes evolve glycolysis, a set of chemical reactions that free the energy of organic molecules such as glucose and store it in the chemical bonds of ATP. Glycolysis (and ATP) continue to be used in almost all organisms, unchanged, to this day.
3800 Ma > Formation of Greenstone belt of the Isua complex of the western Greenland Region, whose rocks show an isotope frequency suggestive of the presence of life.

Archean Eon
3800 Ma – 2500 Ma

3500 Ma > Lifetime of the last universal ancestor; the split between bacteria and archaea occurs.
Bacteria develop primitive forms of photosynthesis which at first do not produce oxygen. These organisms generate ATP by exploiting a proton gradient, a mechanism still used in virtually all organisms.

3000 Ma > Photosynthesizing cyanobacteria evolve; they use water as a reducing agent, thereby producing oxygen as waste product. The oxygen initially oxidizes dissolved iron in the oceans, creating iron ore. The oxygen concentration in the atmosphere slowly rises, acting as a poison for many bacteria. The Moon is still very close to Earth and causes tides 1,000 feet (305 m) high. The Earth is continually wracked by hurricane-force winds. These extreme mixing influences are thought to stimulate evolutionary processes.

Proterozoic Eon
2500 Ma – 542 Ma

2500 Ma > Great Oxidation Event led by Cyanobacteria's oxygenic photosynthesis. Commencement of plate tectonics with old marine crust dense enough to subduct.
2000 Ma > Diversification and expansion of acritarchs.
By 1850 Ma > Eukaryotic cells appear. Eukaryotes contain membrane-bound organelles with diverse functions, probably derived from prokaryotes engulfing each other via phagocytosis. The appearance of red beds show that an oxidising atmosphere had been produced. Incentives now favoured the spread of eukaryotic life.
1400 Ma > Great increase in stromatolite diversity.
By 1200 Ma > Sexual reproduction first appears, increasing the rate of evolution.
1200 Ma > Simple multicellular organisms evolve, mostly consisting of cell colonies of limited complexity. First multicellular red algae evolve
1100 Ma > Earliest dinoflagellates
1000 Ma > First vaucherian algae (ex: Palaeovaucheria)
750 Ma > First protozoa (ex: Melanocyrillium)
850–630 Ma > A global glaciation may have occurred. Opinion is divided on whether it increased or decreased biodiversity or the rate of evolution.
580–542 Ma > The Ediacaran biota represent the first large, complex multicellular organisms - although their affinities remain a subject of debate.
580–500 Ma > Most modern phyla of animals begin to appear in the fossil record during the Cambrian explosion.
580–540 Ma > The accumulation of atmospheric oxygen allows the formation of an ozone layer.This blocks ultraviolet radiation, permitting the colonisation of the land.
560 Ma > Earliest fungi
550 Ma > First fossil evidence for ctenophora (comb-jellies), porifera (sponges), and anthozoa (corals & anemones)


Birth Of The Earth

Scientists estimate that our planet, Earth, formed around 4600 million years ago.  We don't know how old our Earth is, but at least we have some really good evidence to support this hypothesis:
"Earth formed along side with other planets, meteors, asteroids, comets and our sun in our Solar System. The infinite mass of matter collide and fused together, made it bigger and bigger, until finally there were substantial bodies, a planet. The 'left-overs', especially the big-round ones, were pulled in to planet's orbit, a moon and asteroids."

They called this time "Hadean Period", about 4600 - 3800 million years ago. During this period the molten iron sank into the middle of the Earth, become the core. The lighter material rose to the surface, the lightest of all become the Earth's crust. The volatile materials such as water, carbon dioxide! methane, nitrogen, hydrogen and ammonia formed the atmosphere.The initial steam atmosphere was made of water from comets and hydrated minerals from volcanic eruptions. Rain fell into proto-ocean about 4300 to 4400 million years ago. All terrestrial planets are thought to have had a similar process in their early histories.

During the long interval of the Precambrian Era (which includes approximately 90% of geologic time and includes three Eons: the Hadean, the Archean and the Proterozoic) the only inhabitants of the Earth were simple microscopic organisms, many of them comparable in size and complexity to modern-day bacteria. The conditions under which these organisms lived differed greatly from those prevailing today, but the mechanisms of evolution were the same. Genetic variations made some individuals better fitted than others to survive and to reproduce in a given environment. The emergence of new forms of life through this principle of natural selection exerted great changes on the physical environment, thereby altering the conditions of evolution.


The Oldest dated ROCKS

An aggregate of minerals that have not been subsequently melted or disaggregated by erosion, are from the Hadean Eon. Some can be found in the Canadian Sheild, Australia, Africa and in other more specific places around the world.

Oldest terrestrial material
The oldest material of terrestrial origin that has been dated is a zircon mineral of 4,404 ± 8 Ma enclosed in a metamorphosed sandstone conglomerate in the Jack Hills of the Narryer Gneiss Terrane of Western Australia.

Earth's oldest rock formation
The oldest rock formation is, depending on the latest research, either part of the Isua Greenstone Belt, Narryer Gneiss Terrane, or the Acasta Gneiss.

Oldest rock on Earth
The Acasta Gneiss in the Canadian Shield in the Northwest Territories, Canada is composed of the Archaean igneous and gneissic cores of ancient mountain chains that have been exposed in a glacial peneplain.

Non-terrestrial rocks
The Genesis Rock, obtained from the Moon by astronauts during Apollo 15 mission, has been dated at 4.46 billion years. This is one of the oldest known rocks on Earth, even though it originated on the Moon. During Apollo 16, older rocks were brought back.

Acasta Gneiss, the oldest rock known in the Earth.

Genesis Rock, one of the rocks that obtained from the Moon.

Tuesday, May 29, 2012


This timeline of evolution of life outlines the major events in the development of life on planet Earth since it first originated until the present day. In biologyevolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organization, from kingdoms to species, and individual organisms and molecules such as DNA and proteins. The similarities between all present day organisms indicate the presence of a common ancestor from which all known species, living and extinct, have diverged through the process of evolution.