The Biological Foundations of Life and Evolutionary Origins
1. The Chemical Composition of Living Matter
Living matter is composed of approximately 20 of the 90 elements found in nature. Contrary to the Earth's crust, which is rich in silicon and aluminum, living organisms are primarily composed of hydrogen, carbon, oxygen, and nitrogen. Water is the primary medium for these elements. Other essential elements, such as iron, potassium, selenium, and sulfur, are present in trace amounts but are vital for survival.
2. Energy for Life
Life requires both matter and energy. Energy is obtained through chemical reactions involving inorganic matter, primarily synthesized via photosynthesis in plants and algae. To release the energy necessary for life, organisms perform cellular respiration. Based on how they obtain organic matter, organisms are classified into two types:
- Autotrophs: Produce their own food.
- Heterotrophs: Obtain food from other organisms.
3. The Origin of Life
3.1 The Source of Carbon
The nebula that formed the solar system was not particularly rich in carbon, containing 30 times less than the current biosphere. It is believed that carbon emerged from the Earth's interior.
3.2 The Origin of Water
Due to high temperatures near the Sun during the formation of the solar system, water could not condense in inner orbits. The most accepted hypothesis suggests that water was delivered to Earth by asteroids originating from orbits beyond Mars.
3.3 A Stage for Life
Early Earth featured an extremely hot interior with intense volcanism. Because continents had not yet fully formed, most of this volcanic activity occurred underwater.
3.4 The Miller-Urey Experiment
In 1953, Stanley Miller synthesized amino acids using ammonia, methane, and water vapor, simulating the primitive atmosphere. While modern science suggests the early atmosphere may not have contained as much methane as Miller assumed, his experiment remains significant for proving that organic matter can be synthesized from inorganic precursors.
4. Evidence for Evolution
Evolution is supported by three primary types of evidence: paleontological, biological, and molecular.
4.1 Biological Evidence
Biological evidence includes the study of homologous structures, such as the bone arrangements in the limbs of bats, whales, and humans. These similarities suggest adaptations from a common ancestor. Additionally, vestigial organs—body parts that have lost their original utility—provide further evidence of evolutionary history and ancestral lifestyles.