Life on Earth.
1. Analysis of the oldest sedimentary rocks provides evidence for the origin of life. * Identify the relationship between the conditions on early Earth and the origin of organic molecules. * Scientists estimate that the universe is 10-20 billion years old and arose as a big bang, which is still expanding the universe. * The early Earth was very different from the Earth today and no oxygen was present. This means that there was no ozone layer exposing the Earth’s surface to ultraviolet radiation. * There were large amounts of volcanic activity, heat, ash and dust and gases in the atmosphere. * Violent electric storms were common.
* On our Earth, organic chemicals appear to have originated about 4 billion years ago. * Early Earth, with an atmosphere of water vapour, hydrogen, methane and ammonia, provided an environment in which the production of organic molecules would be most likely formed in the lower atmosphere or the Earth’s surface. * The organic compounds of water, carbohydrates, lipids, proteins and nucleic acids are composed of hydrogen (H), oxygen (O), carbon (C), nitrogen (N) and some other elements. * The elements needed to create these organic compounds were already present in the atmosphere in early Earth. * The lack of ozone layer, the frequent violent electric storms and the volcanic activity of early Earth could have provided the energy for molecules to be formed. * Discuss the implications of the existence of organic molecules in the cosmos for the origin of life on Earth. * The discovery of organic compounds on meteorites implies there are organic molecules in the cosmos. This means early Earth may have been ‘seeded’ with organic molecules from the cosmos and the first cells may have arrived from the cosmos. This has led to research in other areas (eg: radio spectroscopy to detect chemicals in outer space and the analysis of interstellar dust).
* Describe two scientific theories relating to the evolution of chemicals of life and discuss their significance in understanding the origin of life. Theory.
| Significance in understanding the origin of life.
| Spontaneous generation.
| Life spontaneously arises from non-living matter (fish came from muddy water; frogs arise from moist earth etc.).
| Spontaneous generation was believed as far as back as the time of Aristotle. However, it was disproven when scientific experiments were carried out (eg: Redi showed maggots did not arise from rotting meat).
| Chemosynthetic theory.
| Oparin and Haldane stated that before living cells could arise, living chemicals must be formed. Biological chemical evolution preceded cellular evolution. Reactions in early Earth lead to the formation of organic molecules. Complex molecules could have been formed and collected together at the surface of the oceans, forming a ‘soup’ which later could have formed cells.
| Urey and Miller carried out an experiment and showed reactions in a reducing atmosphere could lead to the formation of organic molecules. Since then, there have been many experiments to discover conditions and processes that occur which lead to the formation of organic molecules, droplets with membrane, self-replicating molecules and other stages that are needed in the origin of life.
| Some scientists have suggested that our DNA and RNA have come from some other environment outside the Earth and arrived here during the time when early Earth conditions prevailed. There were constant meteorites hitting the Earth, and these meteorites could have contained amino acids.
| The discovery of organic molecules on meteorites has led to further research (eg: NASA probe to discover the extent of organic molecules in the cosmos and its potential role in the origin of life on Earth).
| * Discuss the significance of the Urey and Miller experiments in the debate on the composition of the primitive atmosphere. * Urey and Miller...
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