What are the Essential Ingredients of Life?
Wherever we have found life on Earth, it has had these key ingredients:
Energy + Water + Chemical Raw Materials = Life
As scientists look for life on other worlds, they are looking for places that might have liquid water and some form of energy.
What Kinds Of Energy Support Life?
All organisms require energy to fuel their life processes of growth, maintenance and reproduction.
The known forms of life use two forms of energy - light and chemical. Plants, algae and some bacteria photosynthesize and therefore fall into the first category. Animals, fungi and non-photosynthesizing bacteria fall into the second. Most chemical eaters ultimately depend on photosynthesis to obtain their organic matter and oxygen.
Until recently, we thought that all life cycles were directly dependent on light for their energy. Then in 1977, we discovered deep sea ecosystems that are sustained almost entirely by chemical energy, such as those that flourish around the black smokers in the picture above.
Black smokers dump large amounts of hydrogen sulfide into the surrounding water, which sulfur eating bacteria metabolize. These bacteria form symbiotic relationships with other life forms, such as tubeworms, allowing them to survive where other life forms cannot.
Black smokers dump large amounts of hydrogen sulfide into the surrounding water, which sulfur eating bacteria metabolize. These bacteria form symbiotic relationships with other life forms, such as tubeworms, allowing them to survive where other life forms can not.
Liquid water is required by all known forms of life. It is the only liquid that has been found to facilitate the processes that are the basis of life. Liquid water can dissolve many, but not all compounds. As a result, it can provide a medium for cells (built out of non-dissolving material), and a means of transporting materials in and out of them. Consequently, NASA scientists are "following the water," looking for life on planets that have signs of water.
Martian Ice Cap Courtesy NASA/JPL-Caltech
Mars has features that appear to have been created by flowing water, which makes it a prime candidate for exploration in our solar system.
Some scientists believe that the gully-like features running down the crater walls above were formed by water. Other scientists have suggested that the channels were caused by a process that did not involve water, such as wind or landslides.
This sinuous channel snakes its way across 1000 km. It is likely that it was carved by either lava or water.
In conclusion, we must offer two caveats about life and water. First, although life has always been found in the presence of water, water alone is not enough to support life because other limitations can come into play. These include extreme temperatures such as those found inside hydrothermal vents, where water can be 350°C. That is too hot for life to exist.
Finally, it is also possible that a chemical other than water could be the solvent that supports life, but we have not found it yet.