A planet full of life. The origin of life.

 What is Life?
For scientists there is not a unique concept for life but there are some common characteristics that allow us to distinguish the most essential of this phenomenon.
 Life is a system that uses an environment for reproduction and perpetuation of species.

 The chemical basis of Life: Immediate Principles

http://www.youtube.com/watch?v=PYH63o10iTE 
Immediate principles are biomolecules that are part of living beings. They consist of about 70 chemical elements that are also called bioelements.
 Bioelements can be classified into:
• Primary or essential (CHONPS). Constitute 96% by mass of living matter. They are the key components of the water and organic biomolecules.
• Secondary. Are less abundant (approximately 4 %) but play an essential role in the physiology of living being. Are calcium (Ca), magnesium (Mg), sodium (Na), potassium (K) and chlorine (Cl).
• Tertiary. They are part of living being in a small proportion (0.1%), but they are essential for life as they are involved in many biological processes. Examples: iodine (I), iron (Fe), manganese (Mn), cobalt (Co), selenium (Se), fluoride (F), copper (Cu) , etc.
 Biomolecules, in turn, can be divided into two groups:
INORGANIC: water and mineral salts.
ORGANIC: carbohydrates, lipids, proteins and nucleic acids, made up of chains of carbon and hydrogen and they can be found exclusively in living beings

 Origin of Life

  First Theories about the Origin of Life

Creationism

This is a philosophical doctrin which considers that from the beginning, man has sought explanation of the origin of life. The first cultures linked this to the presence of an omnipotent being (God), although this hypothesis is not scientific by not testing any observable fact that can verify it, however, creationism have survived to this day.

 Spontaneous generation

Experiments conducted between the XVII and XVIII centuries eventually banish this idea. Here is the most important experiment:
Redi's experiment.
Francesco Redi, an Italian physician, performed an experiment in 1668 in which he placed four glasses in which respectively put a piece of snake, fish, eels and a piece of beef. Then prepared another four glasses with the same materials and left open, while the first ones remained sealed. Soon some flies were attracted by food left in open vessels and went to eat and lay eggs; after a period of time, in this series of vessels began to appear some larvae. This is not verified, however, in closed vessels, even after several months. Therefore, Redi concluded that the larvae (maggots) were originated because of flies and not by spontaneous generation.

http://www.youtube.com/watch?v=WNByRghR6sw&list=PLPPRUDh1AoDoc3C7vRZRiYFrbmAzEQQjK
Some people objected to Redi saying in closed vessels had lacked air circulation (which, they said, lay the "vital principle") and that had prevented spontaneous generation. Redi made a second experiment, this time the experiment vessels were not sealed, but only coated gauze. The air, therefore, could circulate. The result was identical to the previous experiment, because the gauze obviously prevented insect access to the vessels and subsequent deposition of eggs and therefore not given birth larvae.
With these simple experiences, Redi showed that putrefying flesh was developed by a larvae action and not by a meat processing, as was claimed by supporters of spontaneous generation.

How could life have begun?

Some people think it was carried to Earth from another planet. But that just puts back the problem of how life began to that other planet. It is simplest to assume that life began on Earth. Indeed, the Earth has the right conditions for life to exist. It is at just the right distance from the Sun for water to be a liquid, and its orbit is almost circular. This is probably unusual among planets round other stars, so it seems sensible to assume Earth was the place where life began. 
Meterorites&Life: http://www.pbs.org/exploringspace/meteorites/murchison/page8.html 

Modern theories about the Origin of Life
 Prebiotic Synthesis: The Origin of Life upon Alexander Oparin
Oparin postulated that 4,000 million years ago, about the time the Earth´s crust cooled, small molecules of atmospheric gases (H2O, methane [CH4 ] and ammonia [NH3]) resulted in a organic molecule called prebiotic, thanks to the energy provided primarily by ultraviolet radiation from the Sun and the constant shock of storms. These prebiotic molecules, more complex, would become amino acids (protein constituent of elements) and nucleic acids. According to Oparin, these first molecules would be trapped in shallow pools formed in the early ocean coastline, forming a prebiotic soup. Afterwards these simple compounds forming polymers were grouped into forming more complex organic molecules. At some point, somewhere a molecule capable of replicating itself would appear and lead the formation and appearance of the first cell.

Origin of life required organizing atoms into larger and larger molecules

We start with some of the commonest atoms in the Universe: hydrogen, oxygen, nitrogen and carbon. These were assembled into smaller molecules, amino acids and bases, which were eventually built into large molecules such as proteins and nucleic acids.

These molecules were certainly present in the atmosphere released by the volcanoes of the young Earth.

This atmosphere probably contained molecules such as methane, ammonia, carbon dioxide and water, but not oxygen molecules. 

The Miller experiment:

Experiments show that energy such as lightning can create amino acids and bases out of these simpler molecules.

http://www.youtube.com/watch?v=mF9U5x6Nxnw 

 They were washed down to Earth in the rain. There they were joined together to make nucleic acids and proteins, perhaps by being heated on the slopes of volcanoes, or on the ocean floor where hot rock rises from the Earth’s mantle.

It is not clear when life began. We guess that it was soon after the meteorite era ended, about 4 billion years ago. All traces of early life on Earth have long since been wiped out. One reason for exploring other planets is the hope that they will show us life at an early stage of formation.

Could life exist on other planets? Our Milky Way Galaxy contains 200 billion stars. If even a small percentage of them have Earth-like planets, then our galaxy could contain many Earth-like planets. Some of them, perhaps, are at just the right distance from their star to be warmed to lukewarm temperatures where the water could be in liquid form and perhaps life could flourish once it had begun. Of these, some must have circular orbits (like the Earth) rather than the more common oval (elliptical) orbit.

But since we do not know how life began, we cannot say how probable it is that it could begin on these other planets.How life began is another of the great unanswered questions .

Creation of life on Earth

Some scientists are trying to create artificial or synthetic life on Earth. In 2010 the J Craig Venter Institute created synthetic DNA which they inserted into a bacterium. However this is still a long way from creating a complete cell from simple chemicals.

And even if they managed to create life in a laboratory, scientists would still be a long way off explaining how life began, when only nature’s laboratory existed.

Reproduction Once life had appeared it spread. If it had not spread it would quickly have been damaged and died out.  http://www.youtube.com/watch?v=dKubyIRiN84  http://www.youtube.com/watch?v=27TxKoFU2Nw Genes were able to reproduce because of the way they were made. First the two halves of the gene were unzipped by an enzyme. Then new genes were built up on each half. In this way two exact copies of the original gene were made Because of the way the bases fitted together, they both carried exactly the same information as the original gene. So these two genes carried the information for exactly the same protein. Life could continue as before. This is called reproduction. Life reproduced and spread.  Mutation Life not only reproduced and spread, it also changed. We will see many changes as we follow the story of life. How did these changes happen? We normally think of mistakes and accidents as bad. But sometimes they are good. Our own mistakes give us the chance to learn, to discover something new. So it was with life. Mistakes sometimes happened when genes reproduced. A base of one nucleic acid could be changed into another base. These mistakes are called mutations. They could be caused by sunlight, by harmful chemicals or by radioactive atoms in the Earth. The two genes which grew upon these two halves were different from each other. They carried information for different proteins. Evolution The world was a test bed where nature could try out the mistakes caused by mutations. The new protein which had been made by accident was given a chance to prove itself. In most cases it was useless, or even harmful, and the life which carried it died. But in a few cases it was useful, and it helped life. It may, for example, have made it grow slightly quicker than other life. After thousands of years other forms of life died out and were replaced by this new form. This process is called evolution by natural selection. By adding together lots of little changes life could slowly evolve into entirely new forms. Notice that evolution depended upon the death of less successful types of life. Death was the price that life paid for progress. The life we see around us has evolved after many small accidental mutations in genes over billions of years. Charles Darwin and the Tree of Life - David Attenborough http://www.dailymotion.com/video/xsxubk_charles-darwin-and-the-tree-of-life-david-attenborough_shortfilms 23-6-14