Evolution

6.1 Origin of Life

The origin of life is a unique and pivotal event in the history of the universe. To understand the origin of life on Earth, it is essential to consider the broader context of the universe's formation. The universe is approximately 13.8 billion years old and consists of vast clusters of galaxies containing stars, gas, and dust. The Earth, part of the solar system in the Milky Way galaxy, formed around 4.5 billion years ago. Initially, Earth had no atmosphere but was covered with gases like water vapour, methane (CH4), carbon dioxide (CO2), and ammonia (NH3) released from molten material. Ultraviolet (UV) rays from the sun broke water molecules into hydrogen and oxygen; the lighter hydrogen escaped, while oxygen combined with other gases to form water and carbon dioxide, eventually leading to the formation of the ozone layer. As the Earth cooled, water vapour condensed and fell as rain, filling depressions to form oceans. Life appeared approximately 500 million years after Earth's formation, about 4 billion years ago. Theories about the origin of life include the idea of 'Panspermia,' which suggests life came from outer space, and the disproved theory of spontaneous generation, which claimed life arose from non-living matter like mud or decaying material. Louis Pasteur's experiments disproved spontaneous generation by showing that life arises only from pre-existing life. Oparin and Haldane proposed that life originated from non-living organic molecules through chemical evolution. They suggested that Earth's early reducing atmosphere, rich in methane, ammonia, hydrogen, and water vapour, under high temperature and volcanic activity, allowed the formation of organic molecules. Stanley L. Miller's 1953 experiment simulated these conditions by creating electric discharges in a mixture of CH4, H2, NH3, and water vapour at 800°C, resulting in the formation of amino acids, the building blocks of proteins. Similar experiments yielded sugars, nitrogen bases, pigments, and fats. Meteorite analyses also revealed organic compounds, indicating similar processes might occur elsewhere in space. The first non-cellular life forms, possibly giant molecules like RNA, proteins, and polysaccharides, may have originated around 3 billion years ago. These could replicate molecules but were not cellular. The first cellular life forms likely appeared around 2 billion years ago, probably single-celled organisms living in aquatic environments. The widely accepted biogenesis theory states that life arose gradually from non-living molecules through evolutionary forces. The exact mechanism of how the first self-replicating metabolic capsules formed remains unknown, but this chemical evolution set the stage for the biological evolution of complex biodiversity on Earth.

• Universe is about 13.8 billion years old; Earth formed about 4.5 billion years ago.
• Early Earth had a reducing atmosphere with gases like methane, ammonia, water vapour, and carbon dioxide.
• UV rays split water molecules; hydrogen escaped, oxygen formed other compounds including ozone.
• Life appeared approximately 4 billion years ago, 500 million years after Earth’s formation.
• Spontaneous generation theory disproved by Louis Pasteur; life arises from pre-existing life.
• Chemical evolution proposed by Oparin and Haldane; supported by Miller’s experiment producing amino acids.
• 📌 Panspermia: Hypothesis that life originated from spores or life units transferred from outer space.
• 📌 Spontaneous Generation: Disproved theory that life arises spontaneously from non-living matter.
• 📌 Chemical Evolution: Formation of organic molecules from inorganic substances under early Earth conditions.

6.2 Evolution of Life Forms - A Theory

The theory of evolution challenges earlier beliefs such as the theory of special creation, which stated that all living organisms were created as they are, that diversity has always been the same, and that Earth is about 4000 years old. These ideas were questioned during the 19th century. Charles Darwin, during his voyage on the H.M.S. Beagle, observed that existing life forms share similarities with each other and with extinct life forms from millions of years ago. He noted that species have undergone gradual changes over time, with some species becoming extinct and new forms arising. This led to the concept of evolution as a continuous process. Darwin proposed that populations have inherent variations in characteristics. Those individuals with traits better suited to their environment have higher reproductive success, a concept called 'fitness.' Fitness refers to an organism's ability to survive and reproduce. Natural selection is the process by which nature 'selects' these fitter individuals to pass on their traits to the next generation. Alfred Wallace, a naturalist working independently in the Malay Archipelago, arrived at similar conclusions about natural selection around the same time as Darwin. The geological history of Earth, with its epochs, periods, and eras, correlates with biological history, showing that Earth is billions of years old, not thousands. The fossil record supports this by showing extinct species and gradual changes in life forms over geological time. Thus, evolution is understood as a process driven by natural selection acting on heritable variations within populations, leading to the diversity of life observed today.

• Theory of special creation posited fixed species created as-is; Earth about 4000 years old.
• Darwin observed similarities among existing and extinct species, indicating gradual evolution.
• Populations have variations; natural selection favors individuals with higher fitness.
• Fitness is reproductive success in a given environment.
• Alfred Wallace independently proposed natural selection.
• Geological and biological histories correlate, supporting Earth’s great age and evolution.
• 📌 Natural Selection: Process where organisms better adapted to their environment tend to survive and produce more offspring.
• 📌 Fitness: The ability of an organism to survive and reproduce in its environment.
• 📌 Special Creation: Religious belief that species were created in their present form and do not change.