do extraterrestrials exist ¿ (73)

Possibly

Ask Yarael if you don't believe!

Life in the universe may have begun "9.7±2.5 billion years ago".
All life on Earth is based upon 26 chemical elements. However, about 95% of this life is built upon only six of these elements: carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur, abbreviated CHNOPS. These six elements form the basic building blocks of virtually all life on Earth.
Life on Earth requires water as the solvent in which biochemical reactions take place. Sufficient quantities of carbon and the other elements along with water, may enable the formation of living organisms on other planets with a chemical make-up and temperature range similar to that of Earth. Terrestrial planets such as Earth are formed in a process that allows for the possibility of having compositions similar to Earth's. The combination of carbon, hydrogen and oxygen in the chemical form of carbohydrates (e.g. sugar) can be a source of chemical energy on which life depends, and can provide structural elements for life (such as ribose, in the molecules DNA and RNA, and cellulose in plants). Plants derive energy through the conversion of light energy into chemical energy via photosynthesis. Life, as currently recognized, requires carbon in both reduced (methane derivatives) and partially oxidized (carbon oxides) states. Nitrogen is needed as a reduced ammonia derivative in all proteins, sulfur as a derivative of hydrogen sulfide in some necessary proteins, and phosphorus oxidized to phosphates in genetic material and in energy transfer.
Pure water is useful because it has a neutral pH due to its continued dissociation between hydroxide and hydronium ions. As a result, it can dissolve both positive metallic ions and negative non-metallic ions with equal ability. Furthermore, the fact that organic molecules can be either hydrophobic (repelled by water) or hydrophilic (soluble in water) creates the ability of organic compounds to orient themselves to form water-enclosing membranes. Additionally, the hydrogen bonds between water molecules give it an ability to store energy with evaporation, which upon condensation is released. This helps to moderate the climate, cooling the tropics and warming the poles, helping to maintain the thermodynamic stability needed for life.
Carbon is fundamental to terrestrial life for its immense flexibility in creating covalent chemical bonds with a variety of non-metallic elements, principally nitrogen, oxygen and hydrogen. Carbon dioxide and water together enable the storage of solar energy in sugars and starches, such as glucose. The oxidation of glucose releases biochemical energy needed to fuel all other biochemical reactions.
The ability to form organic acids (–COOH) and amine bases (–NH2) gives rise to the possibility of neutralization dehydrating reactions to build long polymer peptides and catalytic proteins from monomer amino acids. When combined with phosphates, these acids can build the information-storing molecule of inheritance, DNA, and the principal energy transfer molecule of cellular life, ATP.
Life forms elsewhere in the universe would utilize these basic materials. Life forms based in ammonia (rather than water) have been suggested, though this solution appears less optimal than water.
From a chemical perspective, life is fundamentally a self-replicating reaction, but one which could arise under a great many conditions and with various possible ingredients, though carbon-oxygen within the liquid temperature range of water seems most conducive. Self-replicating reactions of some sort could occur within the plasma of a star, though it would be highly unconventional. Life on the surface of a neutron star, based on nuclear reactions, has also been suggested. However, communicating with such creatures would be difficult because the time scales involved are much faster.
NASA scientist suggested that the color of photosynthesizing pigments of hypothetical life on extrasolar planets might not be green.

The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy.

The Drake equation is based in:

N = the number of civilizations in our galaxy with which communication might be possible (i.e. which are on our current past light cone);
and
R* = the average number of star formation per year in our galaxy
fp = the fraction of those stars that have planets
ne = the average number of planets that can potentially support life per star that has planets
fl = the fraction of planets that could support life that actually develop life at some point
fi = the fraction of planets with life that actually go on to develop intelligent life (civilizations)
fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L = the length of time for which such civilizations release detectable signals into space