Although there may be life elsewhere in our Solar System, we haven’t discovered it yet. The only place we know has life for sure is Earth. Our home planet is at just the right distance from our Sun for liquid water to exist, and has all the other key ingredients to make life possible.

Life is a characteristic that distinguishes physical entities that have biological processes, such as signaling and self-sustaining processes, from those that do not, either because such functions have ceased (they have died), or because they never had such functions and are classified as inanimate. Various forms of life exist, such as plants, animals, fungi, protists, archaea, and bacteria. The criteria can at times be ambiguous and may or may not define viruses, viroids, or potential synthetic life as “living”. Biology is the science concerned with the study of life.

There is currently no consensus regarding the definition of life. One popular definition is that organisms are open systems that maintain homeostasis, are composed of cells, have a life cycle, undergo metabolism, can grow, adapt to their environment, respond to stimuli, reproduce and evolve. However, several other definitions have been proposed, and there are some borderline cases of life, such as viruses or viroids.

Recipe for life

In the mixing bowl are the key ingredients needed for life as we know it:

You will need:

Raw materials, such as oxygen, nitrogen, and carbon
Liquid water
Energy

Raw material

The raw materials needed for life are found all over Earth – for example in soil. However soil needs water and energy from the Sun before life can appear. Life as we know it contains specific combinations of elements including carbon, hydrogen, nitrogen, and oxygen that combine to form proteins and nucleic acids which can replicate genetic code. All the basic elements are formed in stars and distributed throughout space as a result of giant explosions called supernovas. Since these essential chemicals are quite common in other places in the Universe we can expect that the development of life somewhere else is also possible.

Water

Liquid water is essential for life. It allows crucial changes to take place between raw materials. Liquid water is essential because biochemical reactions take place in water. Water is also an excellent solvent that easily dissolves and carries nutrients and other compounds in and out of cells. Life forms are usually made primarily of water. In fact, our human bodies are more than 60% water.

Energy

Life on Earth would not be possible without a constant source of energy, such as the Sun. Organisms require energy to assimilate or put together the chemicals that form an individual. Energy is also required for the organism to grow, reproduce, and respond to the environment. Energy sources may include other organisms, light, or inorganic compounds. The most common source of energy on the Earth is photosynthesis, which transforms sunlight into food. This process will not work very well for the outer Solar System, because not much light reaches such great distances. However, we can look to extremophiles here on Earth for help in figuring out where and what to search for. Extremophiles live in extreme conditions and typically get their energy from a source other than the sun.

 

Picture Credit: Google