How did life start on Earth? Though nobody is ever likely to understand the whole story, virtually everybody has wondered at one time or another, how life on Earth started.
You can find at least three kinds of hypotheses which try to explain the formation of life on Earth. The first and oldest of these hypotheses recommend that life was produced by a supreme being or spiritual force. Many cultures and religions have their own explanations of development that are passed down through generation to generation. Since these ideas cannot be proved nor disproved, we think about them outside the boundaries of science. Because of this, they will not be pursued here and are left to each individual to choose.
The next set of hypotheses suggest that life started in another part of the universe and came on Earth by chance, including with the crash of a comet or meteor.
The third and most frequent hypothesis within the scientific community, is that life started approximately 3.5 billion years back because of a complex sequence of chemical reactions that occurred spontaneously in Earth's atmosphere. In the 50's, two biochemists performed an experiment which demonstrated that certain molecules of life (amino acids) could form spontaneously when the circumstances of Earth's early atmosphere were redone in the lab. It is thought that over time, these molecules interacted with each other eventually resulting in the earliest forms of life.
The initial beings were probably similar to coacervates. As a group, these bacteria are known as heterotrophic anaerobes (ann-air-robes). Because there was virtually no oxygen within the atmosphere at this time, these bacteria were necessarily anaerobic, which means they did not inhale oxygen. Heterotrophs, which means "other feeders", are merely organisms that cannot make their own food. Therefore "heterotrophic anaerobes" means they were creatures that ate some naturally occurring food and did not inhale oxygen. The fossils of some these oldest known types of life have been seen in Australian rocks dating back 3.5 billion years.
To generate energy, these early bacteria probably ingested naturally occurring amino acids. Amino acids, sugars along with other organic compounds created spontaneously in the atmosphere then mixed in liquid water. Upon digesting these molecules, early bacteria made methane and carbon dioxide as waste material. Fermenting bacteria would be an example from today of what these early animals might have been like. To make beer you mix barley or wheat and water. The broken down barley and wheat becomes sugar. Bacteria consume the sugars and create alcohol and carbon dioxide gas as waste material. In the early Earth, the alcohol and carbon dioxide became part of the natural environment.Over time, new life forms evolved that have been able to get their energy through a different source, the Sun.