fr en es pt
Contact the author rss astronoo

Life Under the Ice - The periods of glaciation

Boundary between the living and the inanimate

 Automatic translation  Automatic translation Updated June 01, 2013

Life is a chemical process in which living organisms are derived.
Matter of life is present on Earth and this is certainly elsewhere in the universe for billions of years.
In organics meteorites, the oldest materials, scientists find in, the basics of life that have fueled the primordial soup on Earth, there are 4 billion years.
Life began protecting themselves inside cell membranes, life on Earth is so cell.
A mixture of organic compounds as simple as that contained in a carbonaceous meteorite can form cell membranes and this has contributed to the formation of the first cells on the early Earth.
Scientists foresee the early stages of creating the first living cells, but very old organic molecules and cell membranes do not reveal almost nothing of the mysterious passage of matter to life.
What is certain is that we are made of matter, but at the same time, we will distinguish.
What sets us apart from the matter is that we are alive, not inert. We say that a body is alive if it can feed, grow and reproduce, to pass the time.


Since life is chemical and has its origin in dead matter, why not find the precise boundary between living and inanimate?
A virus for example, is an assemblage of atoms inert, it is dead and yet it acts like a living organism, reproducing and mutant, when it infects a cell.
The lifeless and the living is strangely similar in the crystal that grows and multiplies, while being inert.
Archaea, are cells 10 times smaller than bacteria and their DNA sequence, shows that they are closer to the first living organism than bacteria.
They are found on Earth who live in extreme conditions, which shows their phenomenal capacity to adapt.
That's why researchers are trying to remove the maximum amount of information stored in their DNA, to keep a living organism "minimal" and reach the border between inanimate and living.

 methanogenic microorganisms

Image: Methanogens are microorganisms in the branch of Archaea and are producing methane. This gas has played an important role in evolution.

The reign of the living


Fungi, animals, plants are grouped on the same branch of the tree of life, limb or nuclei of eukaryotic cells. Bacteria represent life in its most simple and yet it can grow and multiply at very high speed.
Bacteria form the second branch of the tree, that of cells without a nucleus or eubacteria (true bacteria).
Archaea represent another distinct branch of the tree.
Scientists classify the living world into three parts, yet the genetic code that can be found everywhere on Earth, is unique. So there is only one form of life on Earth and we have no other life example based on a different chemistry or another genetic code. Are we alone in the Universe is a big question, but it is difficult now to believe that life exists on Earth, wherever there is liquid water, there is a possibility of life even under the icy crust of planets or satellites of planets. Life thrives in places where even the sun's energy does not penetrate, we see on our planet. The oldest fossil bacteria are very old, dating from 3.5 billion years, are the oldest traces of terrestrial life. The oldest rocks on Earth date from 3.9 billion years and the information they contain, we show signs of life. If the signature of the life is present in rocks older is that life began very early with this complexity. One could easily think that it emerges on the planets, because life is intimately linked with the planets. Life on Earth was oriented in one direction over the environmental changes, stress and genetic mutations accidental, leaving the way for some species favor others.


Species well adapted to their environment continue their path and reproduce.
The evolutionary tree shows the extreme diversity of life that was organized from the cellular industry and yet the 3 to 30 million estimated species currently account for barely 1% of all species with lived on Earth. Bacteria specialize and evolve with great speed to adapt and life could start again, from these simple cells.
Contingency prevent the tree of life, to evolve the same way, it will never return to the same evolutionary path, so everything had to start from scratch. To understand life, we must find another form of life to which we compare, for we are prisoners of our tree of life and we can not perceive others. This prevents us to imagine another form of life on a planet other than Earth.
Our Milky Way contains about 140 billion stars, beyond the billions of galaxies also contain 100 billion stars and all these stars harbor planets around them who probably carry life in another form.
There must be an infinite number of worlds in the universe and those other worlds are probably inhabited by life, but how to recognize?
The Universe is the bearer of life and something connects us to the matter, a cosmic connection that we can not, currently imagine.

Image: Tree of life according to the American microbiologist Carl Woese Richard, who defined in 1977, the domain Archaea, one of three domains of life or reign.

 Tree of life, bacteria, archaea, eukaryotes

Very long periods of time on Earth


The Hadean, begins with the creation of the Earth, and ends at the beginning of life, i.e. from -4.5 to -3,9 billion years is the division the oldest geological time, Precambrian (Earth time).
The Achaean is the second geological epoch Precambrian. It extends from about -3.9 to -1,9 billion years. This period saw the appearance of oceans and rain that lasted several hundred million years and the onset of unicellular organisms, prokaryotes.


The Proterozoic is the third geological epoch Precambrian. It extends from about -1.9 to -0.54 billion years. This aeon, sees the emergence of multicellular organisms.
The Phanerozoic eon is covering the last 542 million years. it began the Cambrian geological period, and sees the emergence of small shelled animals and then the explosion of development of varied animal life, until today.

 eons An aeon is a very long period of time, arbitrary time. The history of the Earth, its formation to the present day, is divided into four eons.   duration (billion years)
 Hadéen≈ 4,5 à 3,9
 Archaean≈ 3,9 à 1,9
 Proterozoic ≈ 1,9 à 0,54
 Phanerozoic≈ -0,542 to now

Periods of intense glaciation


The Earth has been long and intense periods of glaciation during its history, among these periods, two of them are particularly important in the evolution of life on Earth.
On every continent, our planet has kept the traces of its past glaciations the ice seems to have covered at times, almost the entire planet.
The first major glaciation in the evolution of life is that of Rhyacien which lies between 2300 and 2050 million years.
The second major glaciation in the evolution of life is that of Cryogenian located between -850 to -630 million years.
There are 2.2 billion years, Earth was completely covered with ice and the mean temperature reached -50°C at the surface. The oceans were frozen to a depth of 1000 meters.
There are 750 million years ago, another episode of intense glaciation happened again, these 2 episodes have allowed life to make great leaps forward in the evolution that would one day give birth to the organizations we know today.
In Central Park, New York, there are glacial erratic A glacial erratic is a piece of rock that differs from the size and type of rock native to the area in which it rests. "Erratics" take their name from the Latin word errare, and are carried by glacial ice, often over distances of hundreds of kilometres. Erratics can range in size from pebbles to large boulders such as Big Rock (15,000 metric tons / 17,000 short tons) in Alberta.  that do not resemble the surrounding rock, transported long distances and abandoned in place.
These are the glaciers of the last major glaciation that have uprooted and moved with them, entire mountain. These boulders show that this place was occupied by glaciers. Scientists have researched similar sites dotted with erratic and they are found everywhere on the continents.


Continental drift, does not precisely define the latitude glaciers. It is through the lava, which retain their magnetic properties, the researchers were able to reconstruct the ice cover on Earth.
Lava flows, dating back 2.2 billion years, have been found in South Africa. The test samples were located at a latitude of this lava near the equator, which means that the entire planet was ice. This was repeated during the ice age that occurred between -850 to -630 million years.
These two episodes of major glaciation are incomparable with the last glaciation that occurred 120 000 years ago, much more catastrophic.
The last glaciation has strongly affected the course of evolution, the melting of ice that followed, precipitated the planet in an intense warming, fostering the emergence of new forms of living organisms.
So the great glaciations have covered the planet in 1000 meters of ice, coming down to the equator at the time, and the oceans were frozen up to 1 000 meters deep, this theory is known under the name Snowball Earth (snowball Earth).

NB: Methane is a greenhouse gas far more potent than carbon dioxide, it played an important role in global warming, after the intense period of glaciation that took place there are 2.2 billion years.

 Bacteria are organisms evolved

Image: Bacterium Methanococcus jannaschii.
Bacteria are organisms evolved. Methanogenic organism that was isolated from fumaroles of hydrothermal vents located at 2 600m deep in the Pacific Ocean. Anaerobic bacterium that uses hydrogen and carbon dioxide as an energy source and produce methane (CH4).
She lives at a temperature between 48 ° C to 94 ° C and extreme pressure of 250 times Earth's pressure.

Earth "snowball"


There are about 750 million years, Earth would have passed through ancient times as a ball of cosmic ice, like Tethys or Rhea, the moons of Saturn, or Jupiter's moon Europe.
On every continent, our planet has kept the traces of its past glaciations the ice seems to have covered almost the entire planet.
This theory is known as snowball glaciation (snowball Earth). The causes of this major climatic event are poorly understood, yet it is after this event that multicellular organisms have appeared on Earth. Two teams from CEA and CNRS have succeeded in modeling across a million years, the evolution of the carbon cycle, climate and position of continents, explaining quantitatively the glaciation. In 1992 and 1998 that scientists hypothesize that the Earth would have experienced in the late Proterozoic, an intense glacial episode.
Continental glaciers and sea ice had reached the equator as indicated by glacial features found on all continents. The assumption made by these specialists is a decrease in the concentration of CO2 in the atmosphere.
What was the cause of the decrease in CO2?
The authors of this publication show that the breakup of the supercontinent Rodinia was able, by itself, cause such global cooling.
There are 800 million years to the era of Neo-Proterozoic, from small continents of the Rodinia super-continent, gathered near the equator, between latitudes 60° north and 60° south, fracture. It is under the effect of a huge volcanic blocks that will disperse and gradually draw the continents we know today.
Inlets and ocean will appear, creating sources humid on the coast, while volcanic activity is continuing its work, covering the continents of basaltic magma.
When the eroded basalt surfaces under the effect of moisture, they consume 8 times more carbon than even granite surface.
It is this consumption of carbon that causes the drop in atmospheric CO2, which gradually settles in the form of sedimentary carbonates in the ocean floor.
When the critical threshold is reached, it triggers a sudden cooling.
The planet will lose about 50 degrees Celsius on average and wrapped herself in a mantle of ice, over a kilometer thick.


The neo-Proterozoic glaciation would be the natural consequence of the splitting of Rodinia the middle and lower latitudes.
The glaciation caused the disappearance of many marine microorganisms, but the tenacious life, sheltering near the ocean hot springs.
Over millions of years, volcanic activity creates more niches that will allow Continental explosion of diversity of macro organisms.
While continuing to release carbon dioxide into the atmosphere, volcanoes are going to raise the temperature to melt any ice.
A world in hot and humid macroorganisms rich, gradually replacing the frozen world of that distant time. New forms of life appear.
On these new continents scattered around the planet, prolonged genetic isolation will enrich the selection of species and populate the Earth with a multitude of organizations, as original as each other.

Is the explosion of Precambrian life!

Image: simulation of the supercontinent Rodinia, for there are 750 million years, according to Torsvik 2003.

 Terre lors des époques glaciaires importantes

Image: Il y a environ 750 millions d'années, la Terre aurait traversé les temps anciens sous la forme de boule de neige cosmique (image d'artiste).

 the supercontinent Rodinia

How the Earth has warmed it?


There are about 750 million years the Earth revolved around the sun as a ball of cosmic ice.
On every continent, our planet has kept the traces of its past glaciations the ice seems to have covered almost the entire planet.
This theory is known as snowball glaciation (snowball Earth).
One of the probable scenarios of warming up, is that the greenhouse effect that would have enabled the world out of its lethargy.
While continuing to release carbon dioxide into the atmosphere, volcanoes are going to raise the temperature until all the ice melt. Despite the glaciers coming down to the equator, volcanic activity continued to emit carbon dioxide (CO2) into the atmosphere, volcanoes piercing the ice caps.
When the concentration of carbon dioxide was sufficient, the Greenhouse broke new ground collapse, freeing the Earth from its grip of ice.
Scientists believe it is, this greenhouse effect, which raised the temperature of the Earth, above 0° Celsius. Carbon dioxide (CO2) has long maintained a high temperature on the Earth, which has enabled many germs to grow.
The first traces of bacterial life on Earth are dated at 3.5 billion years, from the famous stromatolites, stacks of fossil cyanobacteria.
Still observed in Australia, such constructions of bacteria are still alive.


NB: cyanobacteria that produce oxygen in abundance, resulting in the precipitation of methane in the ocean depths. In the presence of oxygen, methane precipitates.
How microbes have survived several ice ages of tens of millions of years?
Under the ice there are hot spots along geological faults, where the heat rises from the depths of the Earth. It is in these hot springs that have sheltered the cyanobacteria, as well as quantities of other bacteria that have benefited from the nutrients produced by cyanobacteria.
After this last major glacial episode, life is a huge evolutionary leap, a multitude of macroscopic life forms appear, Namibia, Libya, Russia, Australia, across hundreds of fossil organisms from a few tens of centimeters have been discovered, this fauna is called the Ediacaran fauna.
This fauna found in southern Australia, shows fossils of the earliest known animals to visible size, animals now extinct.

Image: fumaroles, hydrothermal vents, hot spots, along geological faults. This world hot and humid in the ocean floor, allows the survival of microorganisms during major natural disasters, such as periods of intense glaciation.

 hydrothermal vents

Ediacaran fauna


Ediacaran fauna consists of the oldest known animals of visible size.
It dates from the Precambrian, more specifically the Ediacaran, the last geological period of the Proterozoic era (see Table eons, above).
It owes its name to the Ediacara Hills, located 650 km north of Adelaide in Australia. It is in these hills that we discovered the first fossils of marine organisms complex.
They appeared in the late Precambrian, there are about 565 million years. But these archaic bodies have not survived the Cambrian explosion, which saw new species appear closer to those we know.
We found the fossils show a hundred species of soft-bodied, complex organizations.
Fossils of these animals are left imprints of their form in ancient sediments. These sediments have been preserved by the action of microbial mats that have stiffened the surface, forming a kind of mold.
Despite the large number of fossil records that scientists have, we can not, because the beaches of geological time, to see how progressive evolution of a species. Each species appears suddenly.
The transitional forms still belong to the human imagination, can find similarities between species.

 Charnia, the oldest known fossils of complex organisms

Image: Charnia, the oldest known fossil of a complex organism (-575 000 000 years).

Spriggina floundersi, where we saw an ancestor of trilobites

Image: Spriggina floundersi, where we saw an ancestor of trilobites.

 Kimberella a dipleurozoaire

Image: Kimberella dipleurozoaire presenting a few "similarities"with the current shellfish.

Oxygen has boosted the evolution of life


There are 3.5 billion years, the only organisms on Earth are bacteria.
Why do organizations have changed in size after the second ice age?
Before the advent of life, oxygen was virtually absent from the atmosphere.
There are 2 billion years, at the beginning of the Proterozoic period called by geologists, it becomes a dominant gas.
Oxygen, essential to the cycle of life, is appeared after the first major glaciation, it was present only up to 1% after the second ice age, there are 600 million years ago, scientists believe that it accounted for 20% of the atmosphere, almost like today.
How is oxygen appeared?
Volcanoes contain carbon dioxide which dissolves in the oceans but the ice age, it accumulates in the atmosphere by passing slowly through the greenhouse effect, the mean temperature of -50° C to +50° C . Melting ice is extremely fast and then the warming has been decisive in the history of life.
The greenhouse effect continues, another major disaster devastated the Earth after the episodes of major glaciation. High storm devastated the coast and the warm ocean traces the rich nutrients from the depths.
When the sun's rays back and illuminate the surface, the cyanobacteria that had resisted, into action and invade the oceans.
They carry out oxygenic photosynthesis and can convert light energy into chemical energy used by the cell by fixing carbon dioxide (CO2) and releasing oxygen (O2).
A world rich in oxygen was born, generating sets live larger.


It is through the oxygen that produces great energy, that microorganisms have become macroorganisms. Our cells are eukaryotic type, as these cells through the ages.
Collagen (protein fiber consistency), is there appeared 600 million years with oxygen. This substance is synthesized by cells, has extraordinary properties. As the collagen needs lots of oxygen to structure organizations, it was not until the second episode of major glaciation that life was able to continue its evolution towards more and more organizations alike. Cells containing collagen rapidly multiply and unite with each other with vitamin C to form tissues.
Collagen has allowed agencies to build other more complex organisms, by assembling a multitude of cells between them.

Earth Atmosphere

Earth is about 4 billion yearsPresent earth
Carbon dioxide (CO2) 98 %0,03%
Oxygen (O2) 0,0 % 21 %
Azote (NH2)1,9 %79 %
Pressure (bars)60 bars 1 bar
Temperature (°C) 240 à 340 °C13 °C

credit: book by James Lovelock: The Ages of Gaia.

Image: With fossils, paleontologists give us an excellent picture of life as it existed, there are hundreds of millions of years.

 macroorganisms past

The oases of life


During periods of glaciation, the biochemical life remains protected in the oases of the geological backbone.
It resumes its headlong rush toward the complex, once the conditions again become favorable for their chemical evolution.
A question that obviously remains unanswered, in the theory of evolution is that of the appearance of the first living cell on Earth.
The first forms of life that we discover, are bacteria capable of withstanding extreme conditions. We find that these prokaryotes have existed for billions of years. But they represent a molecular biochemistry and protein already very complex and we thus appear in the fossil record. We find that life evolved over time, taking a path defined by an infinite number of parameters, which makes it unpredictable and indefinable.


It is hard to imagine how such complexity could have originated from inert mineral constituents. Paleontologist Mark Czarnecki is also an echo of this issue.
"The biggest obstacle to proving the theory of evolution has always been the fossil record...
These tracks have never found transitional forms assumed by Darwin. Species appear suddenly and disappear the same way."

Image: The first traces of bacterial life on Earth are dated at 3.5 billion years, from the famous stromatolites, stacks of fossil cyanobacteria.
Still observed in Australia, such constructions of bacteria are still alive.

 stromatolites, stacks of fossil cyanobacteria

1997 © − Astronomy, Astrophysics, Evolution and Ecology.
"The data available on this site may be used provided that the source is duly acknowledged."