In 1859, Charles Darwin published a paper called The Origin of Species. It was the first documented scientific evidence to support the concept of evolution. Evolution is the idea that living things change from generation to generation, producing new offspring which are better adapted to their environment. This process is governed by nature itself. Those animals which are best suited for their environment, are the ones who will survive and reproduce. The variations from generation to generation of a certain species come about through random genetic mutations. Since more organisms are produced than can possibly survive, organisms are forced to compete with each other, and only the ones with "good" genetics will live and reproduce. For example, a species of bird may produce an offspring with a bigger beak which allows this bird to be more efficient at getting food. Since this bird is better adapted to it’s environment than a bird with a smaller beak, it is more likely to survive and produce offspring like itself. In this fashion, species can gradually change and become more and more adapted to their environment. This process of evolution suddenly revealed nature "as a flowing process of constant change and growth instead of as a static, immutable order, unchanged since the moment of creation" (Chandler 2).

Darwin’s work showed that humans, and all living creatures, have evolved over time, and caused many scientists to wonder just exactly where it all began. The first step towards finding out how we were made, was to find out what we are made of. Scientists discovered that all life forms are basically made up of the same fundamental components (Tyson 71). Once these basic components of life were discovered and studied, people began to hypothesize about how they formed and evolved into life. Alexander Operin wrote The Origin of Life on Earth in 1936. This book proposed that the environment on Earth over 3.4 billion years ago was much different than it is now. Operin suggested that the Earth’s early atmosphere contained primarily reduced substances such as methane, ammonia, and water, instead of the high concentrations of oxygen that we now have. The lack of oxygen is important because all known life is made up of what is called organic material, such as amino acids, and oxygen breaks down this organic material. It is thought that through reactions fueled by the sun or lightning, the primitive elements found in early Earth, combined to make organic compounds. It is also thought that these organic compounds were in high concentrations in the primitive oceans, so they were allowed to combine and react freely. The suns ultra violet rays, like oxygen, break down simple organic compounds, but water would have protected these organic compounds from any harm from ultra violet rays (Trefil 35). The exact atmosphere and conditions on Earth 4 billion years ago cannot yet be proven with absolute certainty. But, since life was developed as early as 3.46 billion years ago, it makes sense to conclude that the environment on Earth was welcoming to life (Trefil 34).

Still unanswered though, is the question: can organic compounds be formed from inorganic material? Stanley Miller and noble prize winner Harold Urey are responsible for the most prolific studies in this area (Feinberg 117). They designed, and carried out an experiment which simulated what was believed to be early Earth conditions. The experiment couldn’t have been more simple. All they did was expose a mixture of methane, hydrogen, ammonia, and water to an electric discharge. After a few weeks they had more amino acids than are needed for any Earth life forms, along with some fatty acids, and other organic materials. Whether or not Urey and Miller’s experiment exactly represented the conditions on Earth is not what is most important. What is important, is that this experiment showed that the building blocks for life could be easily formed from common and simple compounds.

Once organic compounds were formed on Earth, it was only a matter of time before they started combining through natural reactions to form more and more complex elements, and eventually life. The step from organic material into living cells is the step which has most scientists mystified. So far, scientists have not been able to create a living cell in a laboratory. But, they only began trying less than 100 years ago. Life on Earth could have taken as much as 500 million years to evolve, so they are not ready to give up on this idea just because they haven’t been able to create life in a mere 100 years (Trefil 34). Scientists recently have been making giant leaps towards creating life in the laboratory. "Until a few years ago, biologists were at a loss to understand how life could have arisen under such conditions. But laboratory experiments have convinced them that self-replicating molecules are relatively easy to assemble" (Lemonick 57). Self replicating molecules are the basis for life, because once a molecule can replicate itself, it can evolve. Once self replicating molecules were formed on Earth, evolution took over, and the rest is history. "From the first few cells, the laws of evolution led inexorably toward the development of ever more complex, sophisticated, and adaptable forms of life, including ourselves, without any unexplainable leaps that might require a miraculous intervention" (Chandler 2). The process from mere chemicals into complex life forms may seem miraculous, until one considers that it took 4 billion years, in which case it seems inevitable.

Some people still would say that it would require too much of a coincidence for complex life to have evolved from simple one-celled organisms, or that we are made too perfectly to have just come about by chance alone. Maybe, but the fact that we are so perfectly adapted to our environment should be the biggest clue that we have been created and shaped by our environment. We were not created by luck, we were created through billions of years of trial and error, which were governed by the laws of nature. We should not be amazed that we fit into our environments so well, for it could be no other way. The similarity between all cells in all organisms is also good proof that we all evolved from the same place. "Many processes in the physiologies of a yeast cell and an elephant, a clam and a redwood, work in essentially the same way" (Trefil 38).

It isn’t necessarily important that we find exactly how life formed on Earth. Even if one decides to discount the somewhat popular scientific belief that life began on Earth through the combination of simple elements as described, it is still a valid and important theory. If we can prove that life is a chemical process, we can then prove that it can occur anywhere in the universe (Cooper 30). Even if life on Earth did not result from this process, it does not mean that life on other planets could not have evolved in this fashion. The most important part about the theory is that is shows that it is possible for life to form from inorganic elements. This idea opens up the door for endless speculation on the probability of life forming elsewhere in the solar system, the galaxy, the universe, and beyond.

We actually don’t have to look far to find another planet where life could exist. That is, unless you consider 200 million miles far. However, at 200 million miles, Mars is one of the closest planets, and the one that most closely resembles Earth. Like Earth, it has volcanoes, polar caps, and water. But, conditions on Mars are a little more harsh than those on Earth. It’s atmosphere is about 1 percent as dense as the Earth’s and it’s composition is much different. It consists of about 95 percent carbon dioxide, with small amounts of nitrogen and argon, and almost no oxygen (Fienburg 272). Due to the lack of oxygen, Mars as no ozone layer, and therefore, is not shielded from the ultraviolet rays of the sun. Since ultraviolet rays break down organic material, the surface of Mars sterile and unwelcoming to organic life. The coldness of the climate also seems to make Mars comparatively unwelcoming to life. The average temperature is -15 degrees Fahrenheit, quite cold when compared to the Earth’s average of 75 degrees Fahrenheit (Chandler 47).

So, Mars is by no means an ideal setting for life, but it is by no means uninhabitable either. While it’s atmosphere is thin, and devoid of a meaningful amount of oxygen, it is still thick enough to carry some clouds of water vapor, and there is a reasonable supply of carbon dioxide (Chandler 41). Water and carbon dioxide are the two necessary ingredients for the process of photosynthesis. Photosynthesis is a process by which plants and some bacteria create energy necessary for life. Usually, photosynthesis results in the formation of oxygen, however, "certain types of photosynthesis are known which do not release oxygen" (Fienburg 273). This means that even though we didn’t detect much oxygen on Mars, life forms could still use processes such as photosynthesis to create the energy necessary for life. "There are many microorganisms on Earth that survive without oxygen, and which are in fact, poisoned by it" (Chandler 69). Not only does this demonstrate the diversity of life, but it also should serve as a warning. If we were to only look for what we expect to find, we could then easily miss what’s really there. In other words, if we had not observed Earth organisms carrying out photosynthesis without the oxygen by-product, we probably would have wrongly assumed that Martian life could not use photosynthesis, because of the lack of oxygen in the Martian atmosphere.

Another aspect of the Martian climate which may lead one to believe it is not fit for life, is the coldness. While it is cold on Mars, it is not unbearably cold. There are some algae in Antarctica which live in the same temperature range that is observed in the warmer parts of Mars (Chandler 47). Due to ultraviolet radiation on the surface, any life on Mars would most likely exist under ground, or under water. Liquid water has not been found on the surface, but the existence of volcanoes on Mars hints at the existence of a warm inner core. This means that hot springs could exist under the surface, providing a more ideal setting for life. On Earth, entire ecosystems have developed around volcanically heated vents in the ocean floor. These organisms get their energy, not from the sun, but from sulfur compounds emitted from the core of the Earth (Trefil 40). Once again demonstrating the diversity of life.

One of the most compelling pieces of evidence for life on Mars, is the recent meteorite discovered in Antarctica which came from Mars. It is thought that this meteorite was knocked lose from Mars some 16 million years ago, and crashed into the Earth about 13,000 years ago (Jaroff 59). In 1984 a meteorite specialist found the meteorite, and in 1993, a geologist discovered that it had come from Mars. After this was discovered, it was analyzed in great detail by many scientists. "The scientists found what appears to be chemical and fossilized residue of tiny organisms that lived on Mars more than 3.5 billion years ago" (Naeye 46). Along with the possible fossils, scientists also found organic molecules, and "tiny minerals inside the carbonate globules that appear to be the residue of biological activity". The two minerals found were magnite, and gregite, which are almost never found on Earth rocks, unless life has been there (Naeye 49). Also found were "tiny tubular and egg-shaped structures" which resemble the size and shape of the smallest bacteria found on Earth (Naeye 49-50). However, many are unconvinced by this evidence, and no one is claiming that this is definitive evidence for life on Mars. William Schopf of the University of California, who has spent most of his life studying microfossils, feels "it’s very unlikely that they have remnants of biological activity" (Kerr 864). Life is by no means the only explanation for what was found in the meteorite. It is, however, a very logical explanation. At the very least, the meteorite has shown that organic molecules once existed on Mars. Under the right conditions and the necessary time there is a possibility that the organic molecules could have evolved into life forms.

Like Earth, we should not regard the conditions on Mars as constant. Just because Mars is cold and barren in present times, does not mean it has always been this way. In fact, there are many reasons to believe that Mars was once warmer and wetter than it is today. "Viking", a spacecraft sent to take pictures of Mars, transmitted photos of "channels which could have been produced by a sudden rush of water". It also "discovered another water-derived feature, valley networks, that seems to have been sculpted by a steady source of running water, either rain, or melting snow" (Cowen 205). According to David Chandler, geologists were unable to find any explanation for the valleys and channels, so have concluded that Mars must have had rivers at one time (66). However, scientists have also been unable to explain how Mars could have sustained the rivers. "Running water would require a thick, carbon-dioxide-rich atmosphere to generate precipitation" (Cowen 205). On Earth, carbon dioxide remains in our atmosphere because of tectonic plate activity. The continental plates shift, and some of the Earth’s land continually sinks below the surface. Carbonate-rich rocks are buried deep underground where they decompose and create carbon dioxide which returns to the atmosphere through volcanic activity. Since there is no evidence of tectonic plate activity ever existing on Mars, life probably could not have evolved in the same fashion as it did on Earth. But, the absence of tectonic plate movement also could have speeded up the process. "The reduced level of geologic activity on Mars may have allowed life on Mars to build up an oxygen-rich atmosphere quickly" (Cowen 205). Liquid water would surely increase the probability of life on Mars, but the lack of liquid water would not rule out the possibility of life. As we have seen here on Earth, life has a way of adapting to many different environments. In the desserts of Africa, "there are kangaroo rats who never drink because they can derive their water from their food chemically" (Cooper 38). Just because an environment seems unlivable to us, does not mean that it is.

The conditions on both Mars and Europa may seem too extreme to carry life. However, here on Earth, many life forms have adapted to some incredibly diverse and harsh conditions. Some fish and crustaceans have been found deep along the ocean floor where there is very little oxygen, and the water pressure is enough to crush any other sea creature. Certain kinds of bacteria have been found living around nuclear reactors, in the midst of radiation. Blue-green algae can be found in pools of hot sulfuric acid or in frigid waters. Some insects even live at temperatures well below freezing, by producing their own kind of antifreeze (Chandler 24-25). There seem to be almost no circumstances on Earth where life cannot sustain itself. It is therefore, a little hard to say exactly what the limits of life are.

We know, at least, that life exists on one planet in our solar system. Our solar system is only one out of a galaxy of billions solar systems, and our galaxy is only one in a universe of billions of galaxies. So, if we were to conclude that life outside us does not exist in our solar system, there is still an infinite amount of space to explore. The conditions for life may be stringent and the process may be slow, but in space there is an endless amount of conditions and an endless amount of time. Given the vast expanse of space, and the uniformity, one would not have to be crazy to think that there could be another planet such as Earth revolving around a star such as the Sun.

Recently, scientists have discovered a few planets outside our solar system. One is 200 trillion miles away and has at least two and a half times as much mass as Jupiter. Another, is also about two trillion miles away, and has more than 6 times the mass of Jupiter (Lemonick 53). Both of these planets are assumed to have atmospheres which largely consist of poisonous gases, and their mass alone would seem to make them uninhabitable. Even though both of these planets are believed to be warm enough to harbor liquid water, they still seem like unlikely places for life. Unfortunately, our present technology does not allow us to detect smaller planets which would be more welcoming to life. All planets are extremely difficult to detect because, at 200 trillion miles, they tend to just blend in with the haze of the star they are orbiting. Nonetheless, the discovery of a few planets around a few stars, would lead one to the logical conclusion that there are more out there. And, "if our solar system is any indication, giant, unpleasant planets are likely to be accompanied by small, friendly ones" (Lemonick 53). So, the discovery of a few large planets, around a few stars, indicates that there are many more planets out there, both big and small.

Since the three most abundant elements on Earth - hydrogen, oxygen, and carbon -, are also the three most abundant elements in the universe, our planet may not be so unique (Feinburg 129). Furthermore, "the elements hydrogen, oxygen, and carbon account for more than 95 percent of the atoms in the human body and all other known life". "If life on Earth were composed primarily of molybdenum, bismuth, and plutonium, then we would have excellent reason to suspect that we were something special in the universe" (Tyson 71). Since the elements which make up life are not uncommon in the universe, there is no reason to believe that life itself is uncommon in the universe. The universe is not very diverse. Every star and planet contained in it is primarily composed of the same three basic chemicals which are necessary for life. This makes the idea of finding another planet like Earth quite reasonable.

The possibilities are out there. The possibilities are endless. The location for life is common, the elements for life are common, it then makes sense to conclude that life is not uncommon. Life is part of the natural cycle of evolution. Life forms are created just as mountains and streams are. The possibility that life existed, or exists, in our solar system somewhere other than on Earth is good. The possibility that life exists somewhere else in the universe is definite. Given the magnitude and uniformity of the universe, it only makes sense to conclude that there is more planets like Earth out there in space.