The process of cellular respiration and the emergence of purple sulfurbacteria led to the creation of the modern day mitochondria.
Before considering the history of life on Earth, we trace the origin of life.
The four stages of the origin of life are listed.
Each of the four stages of the origin of life is explained by at least one hypothesis.
The principle of common ancestry is at the heart of Darwin's theory of evolution and can be traced back to when life began.
Some of the conditions of ancient Earth that gave rise to the first forms of life were described by Darwin.
The first selfreplicating living cell was produced by the Protocell.
The characteristics shared by all living organisms were considered in Section 1.1. metabolism is the chemical reactions that occur within cells.
Living organisms are subject to the forces of natural selection that drive adaptation to the environment.
The molecule of living organisms are called biomolecules.
The first living organisms on Earth would have had these characteristics, but early Earth was very different from the Earth we know today.
Scientists have been able to develop new hypotheses about the origin of life thanks to advances in chemistry, evolutionary biology, paleontology, and other branches of science.
Prior to the existence of cells, simple organic compounds evolved from other compounds.
The building blocks of DNA and RNA are examples of organic monomers.
The organic monomers were joined to form the organic polymers.
There are living cells.
Protobionts have the ability to self-replicate.
Each stage of the origin of life has been tested by scientists.
The processes of a "chemical evolution" precede the origin of life.
Stage 4 is when life first evolved.
Haldane proposed a hypothesis about the chemical origin of life.
The first stage of the origin of life was the evolution of simple organic molecules from the compounds that were present in the Earth's early atmosphere.
The Oparin-Haldane hypothesis suggests that early Earth was made up of water vapor, hydrogen gas, methane, and ammonia.
Ammonia and methane are reducing agents because of their ability to donate electrons.
Their ability to reduce is strong in the absence of oxygen.
Abiotic synthesis is the process of chemical evolution.
The process could have been driven by the early Earth's atmosphere.
Stanley Miller, under the mentorship of Harold Urey, conducted an experiment to test the hypothesis of early chemical evolution.
Solar radiation, especially ultraviolet radiation, was one of the energy sources on early Earth.
Gases that were thought to be present in the early Earth's atmosphere were admitted to the apparatus and cooled to produce a liquid that could be withdrawn.
The liquid was found to contain small, organic molecules which could be used to make large, cellular polymers.
Miller put a mixture of methane, ammonia, hydrogen, and water in a closed system, heated it, and sent it past an electric spark.
Miller discovered a variety of organic acids after a week's run.
Over the years, the Miller-Urey experiment has been tested and reexamined.
Other investigators have achieved similar results by using less-reducing combinations of gases.
A group of scientists looked at 11 compounds produced from variations of the Miller-Urey experiment and found more organic compounds than Miller reported.
Nitrogen gas (N2), not ammonia (NH3), would have been abundant in the primitive atmosphere according to recent evidence.
The Miller-Urey experiment was challenged by the scarcity of ammonia.
The hypothesis was tested for 15 minutes.
The production of ammonia from these vents could have supported the formation of organic monomers.
Minerals that form at deep-sea thermal vents can cause the formation of ammonia and larger organic molecule in cells.
If early atmospheric gases reacted with one another to produce small organic compounds, neither oxidation nor decay would have destroyed them, and the rain would have washed them into the ocean, where they would have accumulated for hundreds of millions of years.
The Oparin-Haldane hypothesis was an important contribution to our understanding of the early stages of life, but other hypotheses have also been proposed and tested.
In the late 1980s, a biochemist proposed that thermal vents at the bottom of the Earth's oceans provided all the elements and conditions necessary to synthesise organic monomers.
The iron and nickel sulfide molecule would act as catalysts to drive chemical evolution.
There is a different line of thinking about comets and Page 319 meteorites.
Scientists have confirmed the presence of organic molecule in some meteorites.
Many scientists believe that the chemical origin of life could have come from these organic molecules.