Early Ideas
Spontaneous Generation
Spontaneous genreration is the idea that organisms could form from unrelated organisms or inanimate objects.
Francesco Redi
Francesco redi preformed an experiment to prove or disprove spontaneous gneration. This experiment involved putting raw meant into three different flasks and sealing them in different ways. One flask was left unsealed, one was sealed normally, and the last one was covered with a gauze. The unsealed one was covered with flies and maggots, the normally sealed one had no sign of life, and the gauze had flies and maggots on top of it, but not on the meat.
The conclusion drawn from this experiment is that all organisms come from other organism. The only meat that contained organisms was accesible by other organisms. This disproves the theory of spontaneous generation.
Louis Pasteur
Louis pasteur conducted a similar experiment where he replaced meat with broth, and instead of sealing the flask, he put on an S shaped neck. His experiment was a little more exact because he boiled the water to ensure nothing living originally was within the flask, and he checked for organisms smaller than the eye could see.
He found no evidence of life until after the flask was removed proving that life could land in it, but not form from it. This means his experiment also disproved spotaneous generation.
Biogenesis
Biogenesis is basically the opposite of spontaneous generation. It is the idea that all living things can only be formed from similar living things.
Modern Ideas
Miller And Urey
Scientists hypothesize that two things happened before life could appear on Earth. The first is that there had to be organic molecules-molecules containing carbon. The second is that the organic molecules must have formed into more complex molecules such as proteins, carbohydrates, and nucleic acids. These are the materials that are absolutely necessary for life. Scientists Miller and Urey conducted an experiment to test if these conditions were suitable for life. They created something that formed the undesirable conditions of early Earth to see what remained.
Organisms were not the important find in this experiment. A basic neccessity of life however known as an amino acid survived. This means that amino acids could've developed the proteins for living things making their existance possible.
The Evolution of Cells
Earliest Organisms On Earth
The earliest organism was known as photosynthetic bacteria.
Effect On Atmosphere
Photosynthetic bacteria created oxygen that majorly impacted the atmosphere. This developed the Ozone that protected the organisms from UV rays. The oxygen produced spread all throughout the atmosphere.
Endosymbiont Theory
The endosymbiont theory states that prokaryotic cells entered eukaryotic cells, and through symbiosis, created their unique functions.