Universe, Earth, and Life Origins: From Big Bang to Protocells
The Origin of the Universe
The Sun is a yellow star located on the outskirts of the Milky Way galaxy. Galaxies are clusters of billions of stars held together by the force of gravity. Before the appearance of the universe, it was empty of matter.
The Big Bang
The Big Bang is a theory that explains how the universe was formed. According to this theory, the universe was formed due to a great expansion of elementary particles. At the beginning, positively charged particles collided in a sea of photons. Through the reaction of protons, helium nuclei attracted electrons, and neutral atoms were formed by nuclear fusion. The first microwave energy, formed by photons at a temperature of -270°C, was discovered in 1965 by Arno Penzias and Robert Wilson.
Formation of a Star
When young, hydrogen (H) is merged in the core to produce helium (He) and neutrons (N). This causes a strong concentration due to He. If the star has a low mass, it moves and forms a white dwarf that slowly cools. When the products reach a certain amount of fusion, nuclear reactions stop, and the star contracts.
The most massive stars undergo successive stages of fusion. The fusion of iron (Fe) is the last stage in which the core is stable. Further fusion generates energy but never absorbs it. When the star’s pressure decreases, it collapses and gives rise to a supernova.
Formation of the Earth
The Solar System began with the so-called solar nebula, a cloud of dust and gas that began to collapse due to gravity. When nuclear fusion occurred, the Sun was born. The rest, due to centrifugal force, turned into a flattened disk known as the protoplanetary disk. Planets of the Solar System began to form from the disk by a process of gravitational accretion. This is how the Earth was formed.
The planet’s core is formed by a sphere of iron (Fe) and nickel (Ni). Above it is the mantle, which consists of silicate minerals. Finally, the crust floats on the mantle. The crust solidified 4,400 million years ago (Ma), and the oceans formed 3,800 Ma.
Plate Tectonics
Plate tectonics is the study of crustal movements due to the mantle. Due to high temperatures, this drift appears on continents. These findings are due to work done by Alfred Wegener. Another proof of continental drift is due to the Earth’s magnetic field. On both sides of the oceanic ridge, it is observed that Fe is magnetized in lines that show a symmetrical pattern.
The Origin of Life
There are different theories of prebiotic evolution:
- Prebiotic Chemistry: Postulated by Alexander Oparin in the 1920s, it states that organic molecules emerged from inorganic compounds on the Earth’s surface and evolved into the most primitive forms of life. He proposed a primitive atmosphere with plenty of free energy, a lack of an ozone layer, and ultraviolet radiation levels well above current levels.
- Clay World: Proposed by Graham Cairns-Smith.
- Pyrite World: Proposed by Günter Wächtershäuser.
In both the Clay World and Pyrite World theories, inorganic substances are used for the arrival of elementary life functions. In the Clay World, life arose from a duplication process of inorganic molecules trapped in clay. In the Pyrite World, the surface of pyrite served as a precursor to cellular organization. This hypothesis has been strengthened by the discovery of molecules near hydrothermal vents. These vents facilitate other processes until the appearance of defined units called protocells.