What is the definition of life 6
Origin of Life
Theory 1: In the beginning there was the primordial ocean
The earth four billion years ago: volcanoes hurl poisonous gases and rocks into the still thin atmosphere. Every now and then asteroids hit, boiling the ocean water. Even in the depths of the primeval sea there is a turbulent picture: a hot liquid flows from bizarre chimneys, so-called "black smokers".
It contains gases and minerals, a chemical cocktail from which simple and increasingly complex organic compounds emerge over time. Living cells are formed that move and multiply.
The strongest evidence for the theory that life in the deep sea originated near hot springs is archaebacteria. They are the oldest forms of life that we know today. All species occur only in very inhospitable biotopes such as in the seepage water from coal heaps, in geysers or in the deep sea.
Theory 2: The "primordial soup"
The "primordial soup theory" is one of the best-known scenarios for the origin of life on earth. In 1953, the young chemistry student Stanley Lloyd Miller astonished the professional world with a simple experiment.
He brings water to the boil in a glass flask - the boiling primeval ocean in miniature. The steam mixes with methane, ammonia and hydrogen, a mixture that swirled over the earth with the volcanic plumes of prehistoric times.
The mixture flows through a piston in which electrodes generate sparks. They are supposed to simulate thunderstorms in the primordial atmosphere. The electrical energy stimulates the gas mixture to react, from which, among other things, amino acids, the basic building blocks of life, are created.
On the one hand, this ingeniously simple experiment was a decisive step forward, but Miller was only on the threshold of life. The mystery of how bio-cells could have evolved from the amino acids in the next act remains unsolved to this day.
Theory 3: Comets as life givers
The "panspermia theory" assumes that life did not arise spontaneously on earth, but came to us from space. Comets may have been an ideal vehicle for bacterial life. The comet's core consists largely of ice. Resistant bacterial spores could thus have reached the earth, protected from cosmic radiation and "infected" it with life.
Upcoming space missions that investigate the interior of comets should clarify whether there is something to the theory. In the comet's core, scientists suspect matter from the time the solar system and the earth were formed, and thus evidence of early life forms.
However, this approach does not answer the question of how life came about in principle, but merely shifts the scene of the origin of life into space.
Oxygen brings the breakthrough
The most exciting chapter in the history of the earth began 2.5 billion years ago: the chemical conversion of the oxygen-free gas envelope into the atmosphere that gives us the air we breathe today.
A billion years after the first organisms, cyanobacteria native to water are changing the living conditions all over the world. These tiny single-celled cells use sunlight for photosynthesis, releasing oxygen as a waste product.
It is thanks to the cyanobacteria and their massive oxygen production that the life-giving gas was able to accumulate in the atmosphere. At present, the proportion of oxygen is around a fifth of our air envelope. It is quite certain that without oxygen there would be no higher life on earth today.
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