* Astronomy

There is a distinct possibility that human life on Earth could have alien origins, including links to the `Red Planet' Mars, scientists and astro-biologists have claimed.
According to project leader John Parnell of the University of Aberdeen in Scotland, scientists Charles ****ell of Britain's Open University and David Morrison, a senior scientist at the NASA Astrobiology Institute in Moffett Field, California, a study of fossilised microscopic life-forms that were sent into space and back inside an artificial meteorite, has revealed that they could have survived in larger and inhospitable terrain.
The three scientists opine that it is possible that simple organisms could have arrived on Earth via meteorites.

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The Drake formula	R - Rate of formation of suitable stars in our galaxy (number per year) Fp - Fraction (percentage) of those stars with planets Ne -Number of "earths" per planetary system Fl - Fraction (percentage) of those planets where life develops Fi - Fraction (percentage) of sites with intelligent life Fc - Fraction (percentage) of planets where technology develops L - "Lifetime" of communicating civilizations (years) R * Fp * Ne * Fl * Fi * Fc * L = N N - Number of communicative civilizations
The Drake Equation,	is named after its creator, radio astronomer Frank Drake; and  is an attempt to answer the question, of how many communicative alien civilizations there are, scientifically by assigning a value to all the relevant terms, from the number of stars born each year in our galaxy to the number of stars with planets, and so on. Play around with the numbers yourself to see what you come up with for the value N (the number of communicating civilizations in the Milky Way).
Microfossils	almost four billion years old can be found. Life must have appeared one or two hundred million years after the earth cooled off sufficiently to have liquid water. This makes one think that life may inevitably develop, given the right physical and chemical conditions on a planet.
All the organisms	living today, even the simplest ones, descended from some initial life form four billion years ago. The first forms of life would have been much, much simpler than anything that we see around us. However, they must have had that fundamental property of being able to grow, reproduce, and be subject to Darwinian evolution.
There is a huge diversity	of organisms, perhaps 10 million animal species and several hundred thousand plant species. However, these are evolutionary latecomers. The history of animals that we have recorded from fossils is only the last 15 percent or so of the recorded history of life on this planet. The deeper history of life and the greater diversity of life on this planet is micro organismsbacteria, protozoans, algae.
How does life form?	The short answer is we do not really know how life originated on this planet. There have been varieties of experiments that tell us some possible roads. We don't know whether life is an inevitable consequence of planetary formation. Certainly, in our solar system there is no shortage of planets that probably never had life on them. Therefore, it's a hard question to answer. I think the way I'd be most comfortable thinking about it is that you probably have to get the recipe right. That is, you need a planet that has a certain range of environments, certain types of gases in the atmosphere, certain types of geological processes at work, that when you have the right conditions, life will emerge fairly rapidly. Despite decades of concerted effort by radio astronomers working on the project known as SETI, the Search for Extraterrestrial Intelligence, we've had no sign of beings elsewhere in the universe. Our home galaxy, the Milky Way, is a big place. It harbours 200 - 400 billion stars and spans roughly 100,000 light-years from one edge to the other, and there are perhaps 100 billion galaxies in the universe.
Most scientists have long believed that	life on Earth began as a "primordial soup" in a lake or pond some four billion years ago. According to that theory, chemicals from the atmosphere combined with some form of energy necessary to make amino acidsthe building blocks of proteinsto create the first primitive organisms, kicking off the evolution of Earth's species. But the primordial soup theory is being increasingly disputed. Many geophysicists now say the Earth did not have enough gases, like ammonia and methane, from which organic material like amino acids could be produced. Instead, a growing cadre of scientists believes that the organic material was instead brought here by comets. The newly formed Earth was subjected to a fierce bombardment of comets 4 billion years ago. According to the "panspermia theory, life in a ready-made form is ubiquitous in the galaxy and is brought by comets to new planets. to read more
In the primordial soup	that produced life on earth, there were organic molecules that combined to produce the first nucleic acid chains, which were the first elements able to self-replicate. According to one of the more accepted theories, these molecules were ribonucleic acid (RNA) chains, a molecule that is practically identical to DNA and that today has the secondary role in cells of copying information stored in DNA and translating it into proteins. These proteins have a direct active role in the chemical reactions of the cell. In the early stages of life, it seems that the first RNA chains would have had the dual role of self-replicating (as is today the case with DNA) and participating actively in the chemical reactions of the cell activity. Because of their dual role, these cells are called ribozymes (a contraction of the words ribosome and enzyme). But there is an important obstacle to the theory of ribozymes as the origin of life: they could not be very large in length as they would not be able to correct the replication errors (mutations). Therefore they were unable to contain enough genes even to develop the simplest organisms. An investigation led by Mauro Santos, from the Department of Genetics and Microbiology at the Universitat Autònoma de Barcelona (Spain), alongside two Hungarian scientists, has shown that the error threshold, that is, the maximum number of errors that may occur during the replication process of ribozymes without this affecting its functioning, is higher than was previously calculated. In practice, this means that the first riboorganisms (protocells in which RNA is responsible for genetic information and metabolic reactions) could have a much bigger genome than was previously thought: they could contain more than 100 different genes, each measuring 70 bases in length (bases are the units that constitute the genes and codify the information), or more than 70 genes, each measuring 100 bases. tRNAs (essential molecules for the synthesis of proteins) are approximately 70 bases long. The discovery has greatly relaxed the conditions necessary for the first living organisms to develop. "This quantity of genes would be enough for a simple organism to have enough functional activity", according to the researchers. Recent analysis into the minimum number of DNA genes required to constitute bacteria, the simplest organism today, considers that around 200 genes are sufficient. But in riboorganisms there can be much fewer genes, since DNA genomes include a number of genes that have the role of making the RNA translation system (which enables proteins to be produced) work, which would not be required in RNA-based organism.
Vittorio Formisano	of the Institute of Physics and Interplanetary Science in Rome says that there is much more methane on Mars: He bases this on the detection of formaldehyde, by the Planetary Fourier Spectrometer (PFS) instrument, onboard the Mars Express orbiter. Formisano averaged thousands of measurements taken by the PFS and calculated that the Martian atmosphere has formaldehyde in concentrations of 130 parts per billion. The gas is being produced by the oxidation of methane and he estimates that 2.5 million tonnes of methane per year are needed to produce it. This figure is vastly higher than the `observed` production of 150 tonnes of methane per year. to read more
The chances of finding life	somewhere else in the Universe depends on how many planets are capable of supporting life. A ccording to new calculations by astronomers at Open University, as many as half of all star systems could contain habitable planets. The team created mathematical models of known exoplanetary systems, and then added Earth-sized planets into the mix. They found that in half of all planetary systems they simulated, the gravity of the gas giants won't catastrophically affect the orbits of these smaller planets, giving life a chance to evolve.
Water is not an essential	ingredient for Life, scientists now claim. All life on Earth is widely supposed to have descended from a common ancestor. One consequence of this is that every organism uses the same general biochemistry. For example, all forms of life make use of proteins made from the same set of building blocks. However, this may not be the only way to do things. There is a common belief that life absolutely requires liquid water. But, scientists now speculate on the possibilities of life could emerge in cold, icy environments, and need just two requirements; a suitable temperature range to allow chemical bonding, and an energy source (for example, the sun or radioactive decay). "Life may even exist in more exotic environments, such as the supercritical dihydrogen-helium mixtures found on gas giants."

Hint:

R - the Milky Way produces about 10 new stars per year (but perhaps as many as 20) Fp - estimated at r 50% Ne - 50%, Fl - estimated at 100 % Fi - 1 % Fc -1 % L - 500 -200000

-- Edited by Blobrana at 22:59, 2007-10-22

In part five of this six-part lecture series, Vikki Meadows describes the impact plants have on planets. She also explains why the type of star providing sunshine may affect the colour of an alien world's equivalent of bushes, trees, and grass.
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John Severson, professor of biology at St. Louis University, is fascinated by his work.
He's just not sure what's he's looking for exists.
Along with teaching conventional biology, Severson is active in the field of exobiology, a sub-discipline of biology that examines the possibility of life on other planets.

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