4.5 billion years ago Earth was a lifeless and inhospitable place. Volcanoes, a lifeless ocean and an unstable atmosphere dominated during Earth's early days. However, a billion years later it was teeming with organisms similar to blue-green algae, actually, a type of bacteria, not true algae. Some people think that bacterial life was carried to Earth form other places in the universe like the movie, "Mission to Mars." However, they still did not figure out where and why life began at a particular condition and situation.

The simplest life is formed basically on nucleic acids and proteins. Nucleic acids and proteins are built mainly from hydrogen, oxygen, nitrogen and carbon atoms that were present in the atmosphere, released from volcanoes. Scientists believe that the energy from heat, lightning, or radioactive elements caused the arrangement of complex proteins and nucleic acids into strands of replicating genetic code. Following the pattern of the formation of life, the ocean had just the right conditions for life to exist.

        Oceans contain a huge amount of water that are essential to life. Liquid water is not only necessary for humans to survive. In fact, it is also essential for the chemistry of all biological systems. Water provides the medium in which the transportation of molecules can occur in reactions. Also, liquid water can permeate, diffuse, and osmosis nutrients easily.  Because water is necessary for all life, scientists consider it a key clue in searching for the origin of life, be it is somewhere on Earth or even somewhere else in our solar system. 

       The oceans occupy 70% of the Earth's surface. Thus, oceans become a location to receive organic matter from the land and the atmosphere as well as from incoming meteorites, comets and the elements of building Nucleic acid and proteins from the atmosphere. Here, substances such as water, carbon dioxide, methane and hydrogen cyanide form key molecules such as sugar, amino acids, and nucleotides. Such molecules are the building blocks of proteins and nucleic acids, compounds ubiquitous to all living organisms. In addition, hydrothermal vents at the bottom have suitable temperature gradients for organic chemistry to occur.

No one really knows where life began. However, the ocean is the place that most people agree on because its particular environment conditions and advantages of liquid water provide a reasonable and believable situation for the beginning of life to occur.