Cosmic Journey: Galaxy Formation, Solar System, and Life’s Dawn

Posted on Mar 28, 2025 in Geology

Components Within Galaxies

Galaxies contain various celestial bodies:

  • Stars: Often accompanied by planets, satellites, and asteroids. The energy generated in a star comes from thermonuclear reactions that transform hydrogen into helium. When a star has exhausted its hydrogen and begins to consume helium, it can eventually become a white dwarf. A supernova is the massive explosion of a star, releasing large amounts of light and radiation, leading to the star’s disappearance.
  • Nebulae: These are masses of dust and gas from which the materials that constitute stars originate.
  • Dark Matter: These are zones of the universe where a large amount of matter accumulates (estimated at 90% of the universe’s matter). Its presence is detected because its gravity affects the rotation of visible matter, despite being invisible (hence ‘dark’).

The Big Bang Theory Explained

The prevailing cosmological model for the universe’s beginning:

  • Time Zero: All matter and energy of the universe would be concentrated at a single point, the primigenial atom.
  • Inflation: Following the great explosion (the Big Bang) of the primigenial atom, the universe extraordinarily multiplied its size. Fundamental particles (protons, neutrons, electrons) and radiation, known as primordial radiation, formed.
  • Primary Synthesis of Hydrogen and Helium: From these initial particles, the first atoms of hydrogen and helium were formed. These elements constituted the first stars and galaxies.
  • Formation of Heavier Elements: Within the cores of stars, nuclear reactions began, necessary to form other atoms like carbon. The formation of the heaviest elements, such as calcium or iron, required the conditions triggered by supernova explosions, which dispersed these elements throughout the universe.

Formation of Our Solar System

The process began approximately 4.6 billion years ago:

  1. There was a nebula of gas and dust, which began to concentrate due to gravity.
  2. This concentration formed a large central mass and a rotating disk around it.
  3. In the central mass, nuclear reactions started, releasing light and heat, resulting in a star: the Sun (initially a protosun).
  4. Once the protosun formed, particles in the rotating disk began to collide and join together through a process called accretion.
  5. Accretion (collision and assembly) of these particles formed larger bodies called planetesimals, which then aggregated into protoplanets.
  6. Each protoplanet gradually cleared its orbit by sweeping up remaining material, eventually becoming the planets we know today.
  7. Life appeared much later, around 3.8 billion years ago, after the Earth’s surface cooled and the crust formed.

Early Earth’s Development

  • Formation of the Terrestrial Protoplanet: Earth formed through the accretion process described above.
  • Differentiation by Density: Due to high temperatures, early Earth was partially molten. This allowed denser materials (iron, nickel) to sink towards the center, forming the core and mantle, while less dense materials (gases) rose to the surface, forming the primitive atmosphere. This early atmosphere had a very different composition from today’s (rich in H₂S, CO₂, water vapor, N₂, H₂, but lacking free oxygen, O₂).
  • Cooling and Ocean Formation: As the planet cleared its orbit, the frequency of large impacts decreased. Temperatures lowered, allowing water vapor to condense, forming the first liquid water masses (oceans) around 4.2 billion years ago.

Primitive Earth Conditions

The environment on early Earth was harsh:

  • Atmosphere: Very different characteristics from today, with high concentrations of CO₂, CH₄ (methane), water vapor, H₂, N₂, and crucially, no free O₂.
  • UV Radiation: Intense ultraviolet radiation reached the surface directly because there was no protective ozone layer.
  • Instability: The environment was highly unstable, with significant volcanic activity, high temperatures, and continuous impacts from meteorites.

The Origin of Life Theories

Oparin-Haldane Hypothesis

This hypothesis suggests life arose gradually from inorganic molecules:

  1. In the primitive atmosphere, ultraviolet radiation broke down simple inorganic molecules (like water, methane, ammonia).
  2. Their constituent atoms (C, H, O, N) became free.
  3. These atoms recombined based on chemical affinity to form simple organic molecules (like amino acids).
  4. These molecules dissolved in the primitive seas, forming the primordial soup (water + organic molecules).
  5. Within this soup, simple organic molecules joined to form more complex organic molecules.
  6. Eventually, these complex molecules organized into the first living entities, likely resembling bacteria. These early life forms, possibly evolving into eukaryotic cells (like algae and plants), would revolutionize the planet.

Hydrothermal Vent Hypothesis

Objections were raised to the Oparin-Haldane scenario (e.g., the primitive atmosphere might have been less reducing than Miller assumed, and the primordial soup in the vast ocean might have been too diluted). An alternative environment proposed for life’s origin is submarine hydrothermal vents, or ‘black smokers’:

  • Environment: These are places on the ocean floor where volcanic gases emanate at high temperatures (around 300°C).
  • Life Forms: Bacteria (thermophiles) capable of withstanding high temperatures thrive in these environments.
  • Advantages for Abiogenesis:
    • They do not depend on solar energy.
    • They offer enclosed cavities within mineral structures where chemicals could concentrate, potentially allowing for the formation of a more concentrated ‘soup’ than in the open ocean.