The Origins and Evolution of Life on Earth

The Chemical Foundations of Life

The components that constitute the majority of life are oxygen, hydrogen, and carbon, which comprise 98% of our body. Water acts as an essential solvent. Living organisms obtain energy through chemical reactions involving organic matter, primarily produced via photosynthesis by plants, algae, and some bacteria.

Energy Production and Metabolism

For organic matter synthesized in photosynthesis to produce the energy necessary for life, a process called cellular respiration is required. Depending on how organisms obtain organic matter, they are classified as:

• Autotrophs: Produce their own food.
• Heterotrophs: Consume other organisms for energy.

The Origins of Life on Earth

Life requires various mechanisms to adapt to changing environmental conditions. The three vital functions—nutrition, interaction, and reproduction—are interconnected. While carbon originates from stars and volcanic activity, the most accepted hypothesis regarding water suggests it was brought to Earth by asteroids from beyond Mars. Life likely emerged underwater, protected by the ocean.

The Early Earth Environment

The early Earth was an oceanic planet with a very hot interior, submarine volcanoes, and a dense atmosphere lacking oxygen. In a historic experiment, Stanley Miller synthesized amino acids from ammonia, water vapor, and methane gas, simulating the primitive atmosphere. Miller suggested this was the primary step for the appearance of life. Alternatively, the Panspermia hypothesis suggests that the first life forms arrived from space.

Evolution and Biological Diversity

Life appeared on Earth approximately 4,000 million years ago. Today, the planet hosts an estimated 50 million species, all sharing common ancestors. Evidence of this history is preserved in fossils found within rocks.

Evidence Supporting Evolution

There are three primary types of evidence supporting the theory of evolution:

• Biological Evidence: Observations of organisms today and their anatomical adaptations.
• Paleontological Evidence: Fossils representing over 7,000 different species.
• Genetic and Comparative Evidence: The study of common ancestry.

Natural Selection and Evolutionary Theory

A species is defined as a group of organisms capable of interbreeding to produce fertile offspring. Charles Darwin, a British naturalist, proposed natural selection as the mechanism for evolution, based on the survival of the fittest. Conversely, Jean-Baptiste Lamarck proposed that organisms acquire new organs or traits to solve new needs or desires for adaptation.