Cosmos Chronicles: From Big Bang to Humanity
Our Place in the Universe
1. The Origin of the Universe
The Sun is a yellow star that orbits a galaxy called the Milky Way. The Universe is inconceivably great and is full of galaxies (clusters of billions of stars linked by gravity). These galaxies are moving away from us because the universe is expanding. Projecting back, the universe’s energy, mass, and space were gathered in a very high-density state. This marked the beginning of everything, including space and time. Before this, the universe was empty of matter. Thus, 13.7 billion years ago, all the energy density transformed, creating an almost infinite number of elementary particles. This was the Big Bang.
In the first minutes of its existence, the universe was full of charged particles constantly colliding with photons. About 300,000 years later, the energy decreased enough for particles to react and form the first neutral atoms through nuclear fusion. The primordial photons cooled, becoming the cosmic microwave background, discovered by Arnold Penzias and Bob Wilson.
The Genesis of the Elements
Fred Hoyle described the stages of a star’s evolution after the Big Bang. Young stars fuse hydrogen into helium and a little nitrogen. This process continues for thousands of years until the helium amount is so high that the star collapses. If small, it becomes a white dwarf that slowly cools. If massive, it continues fusing elements up to iron, which absorbs energy instead of producing it. The star then collapses, forming a supernova, during which other elements are created.
2. The Formation of the Earth
The solar system began with the solar nebula, which collapsed due to gravity. Mass energy, due to centrifugal force, converted into a protoplanetary disk. Planets formed through gravitational accretion, where particles joined together. Initially, Earth was extremely hot, leading to the formation of its layers: the core (iron and nickel), mantle (silicates), and crust. The crust cooled and solidified 4.4 billion years ago.
Plate Tectonics
Although the mantle is solid, it flows due to plate tectonics and continental drift. Alfred Wegener discovered that continents fit together, supported by evidence like the Earth’s magnetic field, which changes position and shows mirrored patterns on either side of the Atlantic ridge. If we reversed continental movement, we would form the supercontinent Pangaea.
3. Exploring the Solar System
The first step was exploring the Moon. Probes and satellites studied the feasibility of landing humans on the lunar surface, leading to several space missions. Spacecraft have also observed other planets like Mars, Venus, and Jupiter. Space stations are essential for space visits, enabling work under challenging conditions. Recently, there has been a focus on developing space law.
4. The Origin of Life
Several theories explain the origin of life. Oparin’s theory of prebiotic chemistry suggests that organic molecules arose from inorganic compounds in a primitive atmosphere with high free energy. Experiments simulating these conditions have produced organic molecules. Other theories include the clay world and pyrite world hypotheses. Hydrothermal vents, where biodiversity thrives on sulfur, have also been discovered.
5. Evolutionary Theories
Several theories explain biodiversity and evolution. It is believed that all life evolved from LUCA (Last Universal Common Ancestor). Key concepts include morphological changes in species and natural selection. Adaptation, driven by a good genetic endowment, is crucial for biological evolution. Morphological changes are now known to be caused by DNA changes. This explanation, called neo-Darwinism, is based on chance. Fossil records provide supporting evidence.
6. The Homo sapiens Hominid
Our species’ characteristics include a highly developed brain, tool-making ability, language, and bipedalism. Africa is the cradle of hominization, with the oldest hominid remains (Toumai) found there. Species close to us include Australopithecus, Homo habilis, Homo erectus (and ergaster). The latter gave rise to Homo neanderthalensis and then to Homo sapiens, which appears to have originated in Africa.