The Neccessity of Oceans:

The fossil record of the Earth indicates that the first single-celled creatures, blue-green algae, appear 3.5--3.8 billion years ago. Multi-cellular creatures appeared roughly 900 million years ago, and more complex forms started to appear around 600 million years ago. This straightforwardly shows that however life evolved from the simple to the complex, it took hundreds of millions of years. It is quite likely that large bodies of liquid are required to foster such evolution, for two principle reasons:

  • Simple organic molecules are easily photo-dissociated by ultraviolet radiation. Since there was no ozone layer in the early history of the Earth, the only way to protect these primitive organic molecules (or amino acids ) would be immersion in water as water is a strong absorber of UV radiation.

  • A liquid medium provides a transport mechanism for these molecules to move and randomly interact with each other. Quite possibly, it was millions of years of random interactions and a trial-and-error process which produced the genetic code DNA that is the basis for life on this planet.

But if large liquid oceans are necessary for the formation of life, the Earth finds itself with an immediate problem in that most of the water that was present in the inner solar system originally had been boiled away prior to its formation. However, in the outer part of the Solar System, there was a great deal of left over icy material in the form of cometesimals. The masses of the outer planets (Jupiter, Saturn, Uranus and Neptune) are very large and act to eject much of this cometary debris completely out of the Solar System (and into the Oort cloud ). Jupiter served as a "focusing mechanism" and redirected much of this cometary debris into the inner Solar System where it bombarded the newly formed rocky planets. Thus, most of the water that is currently on the Earth was delivered via cometary collisions and quite possibly, if it were not for the position and mass of Jupiter in our Solar System, the Earth would have far less water than it does.

The Formation of the Ozone Layer:

Throughout most of the history of the Earth, life was confined to the ocean. As photosynthesis increased, more and more oxygen was deposited into the Earth's atmosphere. Ozone is formed via the following reaction:

O + O2 + M ==> O3

In order for this reaction to occur both monotomic oxygen (O) and diatomic oxygen (O2) must be present, in the vicinity of another molecule (usually nitrogen) which acts as a catalyst. In general, O is only found at the top of the Earth's atmosphere as it is formed by the UV photo-dissociation of O2. O2, however, is generally found at the bottom of the Earth's atmosphere (as it's produced by surface processes). When sufficient O2 was finally built up, the reaction could occur at a region of the atmosphere where the abundances of the three ingredients necessary to form ozone was optimal. This position is 10-20 km above the surface of the Earth. This region is known as the stratosphere which is the layer above the troposphere where most of the active weather occurs.

Once the ozone layer forms, there is now a significant protective layer which can allow organisms to move from the sea to the land. Shortly after species migrated from the sea to the land, species diversification exploded as there were many new ecological niches to fill. Through tenacity and resilience, evolving life on the land withstood tremendous disasters such as earthquakes, volcanos, major ice ages, occasional asteroid impacts, and slowly intelligence evolved.