Our planet formed as a molten mass about 4.5 billion years ago. It was probably a combination of meteorites and other universal matter crashing together. Upon its formation, it was under a continuous barrage of space matter, including more meteors. It was nothing like our earth today; it was uninhabitable by life, as we know it. The surface was unstable; there was no liquid water; the atmosphere was toxic to life like us.
After about a half a billion years, by scientific theoretical estimates, the earth began to cool and water began to liquefy and settle. Oceans of salt water began to form across the surface, though the exposed land mass was still unstable. Volcanoes continued to erupt constantly, electrical storms were common in the atmosphere, ultraviolet radiation reached the surface in large amounts, and the atmosphere continued to house large amounts of nitrogen and carbon dioxide.
Through experiments, scientists have come to a conclusion of the most likely way life formed. By replicating the conditions we believe were present on the earth 4 billion years ago, scientists have been able to spontaneously create the building blocks of life – DNA. Perhaps in a shallow seashore pool, or maybe in the mineral rich waters of the deep ocean, a jolt of electricity formed these same carbon-based chemical combinations, creating the necessary components for life.
Those building blocks included DNA, or deoxyribonucleic acid. This one chemical combination is responsible for all of life on earth. This carbon-based nucleotide controls the division and replication of cells, and the development of all life, as we know it.
The next step is still a mystery… from the building blocks to the reproducing cells hasn’t been reproduced by science. Still, we know that the first life was single celled organisms much like the single celled bacteria that are still around today. Cells are permeable sacks of chemicals. The exterior membrane contains the carbon-based building blocks of life and allows certain chemicals in and others out, controlling the necessary environment to reproduce.
From these first cells came photosynthesis, which evolved into plants, as we know them today and also began to change the atmosphere, creating a greater proportion of oxygen to allow other life forms to evolve as well.
The next step was multi-celled organisms. As cells divided, some stuck together, creating the first multi-cellular organisms. Eventually, some cells began to live inside other cells, another necessary step for plant life. It is believed that the first photosynthesizing cells began to live inside other cells, and eventually morphed into chloroplasts.