Meteorites
In 1969 a meteorite fell to Earth near the town of Murchison, Victoria in Australia. Studies on fragments of this meteorite have found that it contains molecules crucial to life, leading to the development of the theory that meteorites may be responsible for the origin of life on Earth.
The Murchinson meteorite contained common amino acids, such as glycine and alanine, but also rarer ones, including Isovaline. Tests on Uracil and Xanthil showed that these amino acids contain a higher percentage of the Carbon-13 isotope than is found in the terrestrial amino acids, providing evidence for their extraterrestrial origin. The meteorites also contained sugar acids and alcohols. Sugars are crucial for life as they are components of DNA, RNA and cell membranes, as well as being the main energy source for cells.
The main period in Earth history when meteorites collided with the planet is called the Early Bombardment and occurred between 3.8 and 4.5 billion years ago. It is believed that, not only did these meteorites contain molecules crucial to life but that they also created hydrothermal conditions, similar to those in deep sea vents. The energy of the meteor impact would have generated enough heat to melt rocks for miles around. Along with an abundance of water, these conditions would have been perfect to catalyse the chemical reactions responsible for the beginning of life. Additionally, the early meteor impacts made rocks more porous and, in turn, more hospitable.
Some scientists believe that the concentrations of sugars and amino acids found in the Murchison meteorite are too low for meteorites alone to be responsible for the origins of life. However, if enough meteorites fell to Earth during the Early Bombardment, it is possible that they made a large impact on life originating. As meteorite bombardment in the early Universe was ubiquitous, it is possible that the "seeds of life" were sown on many other planets but only Earth had the ideal conditions at the time to catayse the reaction necessary to create life.
Further reading, some articles on the early bombardment;
http://news.nationalgeographic.co.uk/news/2002/07/0725_020725_meteor.html
http://www.livescience.com/5426-life-survived-earth-early-bombardment.html
The Murchinson meteorite contained common amino acids, such as glycine and alanine, but also rarer ones, including Isovaline. Tests on Uracil and Xanthil showed that these amino acids contain a higher percentage of the Carbon-13 isotope than is found in the terrestrial amino acids, providing evidence for their extraterrestrial origin. The meteorites also contained sugar acids and alcohols. Sugars are crucial for life as they are components of DNA, RNA and cell membranes, as well as being the main energy source for cells.
The main period in Earth history when meteorites collided with the planet is called the Early Bombardment and occurred between 3.8 and 4.5 billion years ago. It is believed that, not only did these meteorites contain molecules crucial to life but that they also created hydrothermal conditions, similar to those in deep sea vents. The energy of the meteor impact would have generated enough heat to melt rocks for miles around. Along with an abundance of water, these conditions would have been perfect to catalyse the chemical reactions responsible for the beginning of life. Additionally, the early meteor impacts made rocks more porous and, in turn, more hospitable.
Some scientists believe that the concentrations of sugars and amino acids found in the Murchison meteorite are too low for meteorites alone to be responsible for the origins of life. However, if enough meteorites fell to Earth during the Early Bombardment, it is possible that they made a large impact on life originating. As meteorite bombardment in the early Universe was ubiquitous, it is possible that the "seeds of life" were sown on many other planets but only Earth had the ideal conditions at the time to catayse the reaction necessary to create life.
Further reading, some articles on the early bombardment;
http://news.nationalgeographic.co.uk/news/2002/07/0725_020725_meteor.html
http://www.livescience.com/5426-life-survived-earth-early-bombardment.html