![]() Plausible sites for prebiotic synthesis are hot sea vents, fumaroles and hot springs, where strong temperature gradients and high water pressure can be found, in addition to minerals. Furthermore, different places on early Earth could have had distinct environmental features that yielded different sets of complex organic molecules. ![]() However, it shows that complex organic molecules can be formed by physicochemical reactions. It does not prove that the origin of life was like this. This was the experiment carried out by Miller and Urey when they were trying to replicate the earliest environment on Earth (Figure 2). If a flask containing CO 2, ammonia, methane and hydrogen, is heated to high temperature and exposed to electric discharges, some complex organic molecules are obtained, such as hydrogen cyanide, formaldehyde, some amino acids, some sugars, purines and pyrimidines (necessary for nucleotide synthesis). a) Terrestrial origin under extreme environmental conditions. How were they synthesized in the early Earth? There are several plausible scenarios. The most relevant are proteins, nucleic acids, sugars and fat. Organic molecules, plus water and some ions, are the building blocks of living organisms. We can imagine the steps, starting from simple molecules until the appearance of the first cells, as follows: Temporal sequence of some relevant events since the beginning of life on Earth. It means that the physicochemical processes leading to the first living organisms should have started earlier, in a period called the prebiotic era.įigure 1. The fossils indicate that the first cells were already on Earth between 3500 x 10 x 10 6 years ago (Figure 1). The Earth is about 4500 x 10 6 years old. Hydrothermal vents show temperature and ions gradients that favor mineral catalysis to form complex molecular systems that evolved into the first cells. It has been suggested that these place were near to hydrothermal vents in the ocean or hot springs in the sweet water, with a rich mineral content. Organic molecules were concentrated in some places where it is supposed that the first cells emerged. ![]() However, it is not excluded that many of these early organic molecules were synthesized in other planets and in the outer space, and came to the Earth as rains of asteroids and comets. These molecules may have been generated in different terrestrial environments and accumulated in the water. Scientists agree that the first cells emerged from organic molecules in the early Earth. Some of the most popular ones are the following:Ī) Reproduction and transmission of information encoded by deoxyribonucleic acid (DNA).ī) Maintaining homeostasis by using external energy (metabolism).Ĭ) Ability to respond to external and internal stimuli.ĭ) Ability to evolve by Darwinian evolution (variation and natural selection).Į) Some others. Nowadays, scientists often define life as a set of properties that an organism should fulfill to be considered as a living organism. However, there is a new problem: what is life? There is no one definition of life that is widely accepted by the scientific community. It could be said that life is one of the properties that a living organism must have. When searching for the origin of life, it is first necessary to know what a living organism is. Physicochemical conditions, similar to those present on Earth during the origin of life, may have occurred elsewhere in the Universe. A cell could be made from scratch by using molecules that exist in current cells and placing them together into a membrane bound compartment. The origin of life as a physicochemical process has consequences in the field of biology. Haldane proposed the first physicochemical theories on the origin of life (also suggested by C. In the twenties of the 20th century, A.I. It is unknown how the first cell appeared on Earth, but it is widely accepted that it was by physicochemical processes. Summary Content Extended This page content
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