The earth was created more than 4 billion years ago, although more than 2 billion years probably passed before life was developed. Scientists believe that the atmosphere of the young earth was mostly water vapor, methane, and ammonia, with very little gaseous oxygen. Laboratory simulations have shown that all major classes of organic molecules could have been generated from this atmosphere by the energy of the sun or by lightning and that the lack of oxygen would prevent newly formed organic molecules from being broken down by oxidation.

Randomly formed aggregations that could harness energy to grow and reproduce themselves would eventually far outnumber other combinations. DNA may have been an important component of the self-reproducing aggregates and RNA is the only organic molecule able to duplicate themselves. The absence of oxygen from the atmosphere of the young earth meant that no ozone layer existed to screen out ultraviolet rad

iation and no oxygen was available for aerobic respiration. Therefore, the first cells were probably photosynthetic and used ultraviolet light. Because photosynthesis generates oxygen, the oxygen content of the atmosphere gradually increased. As a result, cells that could use this oxygen to generate energy, and photosynthetic cells that could use light other than ultraviolet, eventually became predominant.

The endosymbiosis theory suggests an explanation for the existence of certain cellular structures in eukaryotic cells. According to the theory, complex eukaryotic cells evolved from the symbiotic relationship (living together) between larger cells and smaller cells that started as either undigested meals or parasites of the larger cells. Endosymbiosis (living together inside) is not uncommon in nature; however, this theory suggests that mitochondria and chloroplasts originated as free-living organisms, and that modern eukaryotic cells are essentially communities of different cell types living cooperatively.

Professor Kwang Jeon's Supporting Discovery at the University of Tennessee. In 1987, Professor Jeon noticed that his collections of amoebas were developing a large number of dots. This large number of dots turned out to be bacteria, which were quickly killing off Jeon's collection. Jeon noted the least sick ones and began keeping records of their progress. The least sick ones apparently were more resistant to the bacteria since they survived and returned to their normal modes. However, some 40,000 of the invading bacteria were

Some common words found in the essay are:
, Academy Sciences, Professor Jeon, DNA RNA, mitochondria chloroplasts, eukaryotic cells, University Tennessee, cells cells, host cell, protein synthesis, cells cells nuclei, mitochondria chloroplasts own, resembles prokaryotes, evolved symbiotic relationship, genetic material, structures eukaryotic, atmosphere earth, similar prokaryotic,
Approximate Word count = 1045
Approximate Pages = 4 (250 words per page double spaced)