Chapter 1: Cosmology and the Birth of the Earth

8 billion years ago. The content begins with historical models of the cosmos, contrasting geocentric perspectives with heliocentric understanding, then introduces observational evidence for an expanding universe through the Doppler effect and redshift phenomena, which indicate that distant galaxies are moving away from us. The Big Bang theory is presented as the dominant cosmological model, supported by cosmic background radiation and the abundance of light elements observed throughout space. The chapter explains stellar nucleosynthesis—the process by which stars forge heavier elements within their cores—and how supernovae distribute these elements across space, connecting the heavy atoms in human bodies to ancient stellar processes. The focus then shifts to our solar system's formation through the nebular hypothesis, describing how a rotating disk of gas and dust surrounding the young sun gradually accumulated into planetesimals, which collided and merged through accretion to form planets. Earth's internal structure developed through differentiation, as denser materials sank toward the center to form the core while lighter silicates formed the mantle and crust. The chapter addresses the origin of Earth's moon, most likely formed through a giant impact event, and describes how the early atmosphere and hydrosphere developed through outgassing and chemical processes. Throughout the content, emphasis is placed on the interconnected nature of cosmic, stellar, and planetary processes, establishing that Earth represents one outcome of universal physical laws operating across vast scales of time and space.