The Earth’s early atmosphere was probably made up of mainly substances like water, carbon monoxide, hydrogen sulfide, hydrogen cyanide, nitrogen, and carbon dioxide.

There was very little or perhaps no oxygen in the atmosphere at all at this time. There would have been a lot of water vapor in the atmosphere because the Earth was too hot for water to remain a liquid, so it all evaporated and stayed in the atmosphere.

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Stanley Miller and Harold Urey’s important experiments proved that very simple substances could create organic molecules. Their experiments produced several different amino acids, which are the building blocks of proteins.

Miller and Urey used methane, ammonia, water, and an electric current (which was used to simulate lightning strikes) which they believed at the time to create a similar environment to that of the early Earth. These experiments yielded many organic compounds that were once thought to be too complex to arise from inorganic sources, such as amino acids.

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The addition of large amounts of oxygen to Earth’s atmosphere killed many of the bacteria that could not handle existing in the presence of oxygen. Other bacteria like this, called anaerobic bacteria, found places to hide and live where oxygen does not exist in large quantities. Other bacteria developed ways of using oxygen to become more efficient and create more energy.

The early bacteria all evolved in an atmosphere where there was little or no oxygen present. These bacteria were not able to continue to live in the presence of oxygen once it built of in the atmosphere because oxygen is very reactive and damages cells and molecules if cells do not have ways of protecting themselves against its harmful effects. Many bacteria died out because they could not adapt to the oxygen-rich atmosphere, and the only ones of this type that are left today are descended from those that found places to live where there was very little or no oxygen, such as deep in the ground or deep in the oceans. Others were able to adapt and protect themselves from oxygen’s harmful reactivity and some of those developed ways of using oxygen in their energy creating processes to make them more efficient (cellular respiration).

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The endosymbiotic theory hypothesizes that mitochondria and chloroplasts were once actually free-living prokaryotic cells that became engulfed by the earliest eukaryotic cells and began to live in harmony with them as one organism.

Mitochondria and chloroplasts are very similar to free-living prokaryotic cells. They have similar plasma membranes, similar DNA, and similar ribosomes. They even divide the same way prokaryotes do. This led scientists to hypothesize that they were once separate organisms but began to live inside of larger eukaryotic cells and created a mutually beneficial relationship with them.

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Hypothetically, creating life out of non-living things is possible considering that there is a notion saying that the universe began from nonliving matter and the biological factors are influenced by non-living components in the environment. Despite the endless possibility, the only explanation that is proven was the concept of biogenesis which states that living things came from pre-existing living things. Therefore, life could not arise from nonliving matter as of today but there is a possibility that it might happen in the future.