Universe, Earth, and Life: An Evolutionary Journey
The Origin of the Universe
Our sun is a star orbiting in the outskirts of the Milky Way galaxy. The universe is vast, full of clusters of billions of galaxies bound together by gravity. These galaxies are not stationary; they are moving away from each other, indicating that the universe is expanding. Before the universe as we know it, there was an empty void of matter. 13.7 billion years ago, all the energy density from this primordial universe transformed into matter, creating countless elementary particles. The pressure from these particles caused space to expand rapidly—the Big Bang, a widely accepted theory for the origin of our universe.
The Formation of Earth
The solar system began as a solar nebula, a cloud of dust and gases that collapsed under its own gravity. The core contracted, increasing in temperature until nuclear fusion ignited, birthing the sun. This illuminated the surrounding gas and dust, which, due to centrifugal force, flattened into a protoplanetary disk. Planets formed within this disk through gravitational accretion: dust particles attracted each other, forming larger particles with more mass and gravity, attracting even larger particles, and so on. Earth formed approximately 4.57 billion years ago. Initially extremely hot and molten, heavier elements like iron sank to the core, while lighter elements rose to the surface, leading to the differentiation of layers: a core of iron and nickel, a silicate mantle (the thickest layer), and a crust where continents reside.
Tectonic Plates
Despite being solid, the mantle’s high temperature makes it plastic and allows for slow convective motion. This is related to continental drift, as continents float on the mantle. The upper mantle and crust are composed of tectonic plates that interact, influencing geological processes. Alfred Wegener’s theory of continental drift is supported by evidence such as the interlocking coastlines of South America and Africa, similar fossil faunas on both continents, and symmetrical magnetic patterns on either side of the Atlantic ridge.
The Origin of Life
The theory of prebiotic chemical evolution (Oparin) proposes that in an early oxygen-free atmosphere, organic molecules arose from inorganic compounds, eventually evolving into the most primitive life forms.
Evolutionary Theory
Creationism vs. Darwinism
Creationists believe species have always existed as they were created. Darwin’s theory of evolution centers on the concept of change. Species share common ancestors, and the formation of new species is a slow, gradual process driven by natural selection. Natural selection involves variations in morphology, adaptation to the environment, and the survival of the fittest.
Punctuated Equilibrium
This theory (Eldredge and Gould, 1972) suggests evolution occurs in bursts rather than gradually.
Neo-Darwinism
Neo-Darwinism addresses challenges to Darwin’s theory, such as the lack of transitional fossils, inconclusive evidence for natural selection, and the apparent youth of Earth (a misconception later corrected).
Fixism
Fixism posits that all existing life forms are unchanged and have always existed in their current state.
Neo-Lamarckism
Neo-Lamarckism incorporates the inheritance of acquired characteristics.
Hominid Evolution
Australopithecus africanus → Homo habilis → Homo erectus → Homo sapiens neanderthalensis → Homo sapiens sapiens