A Brief Account of Evolution
The narrative of evolution reflects the transition from simple to complex life forms, emphasizing key historical events. Approximately 2000 million years ago, the first cellular forms of life emerged on Earth. Although the exact mechanism of how non-cellular aggregates of macromolecules evolved into cells remains unknown, speculations exist that early cellular structures possessed photosynthetic capabilities akin to modern light reactions, splitting water using solar energy.
Over time, single-celled organisms diversified into multicellular forms. By around 500 million years ago (mya), invertebrates flourished, and jawless fish evolved approximately 350 mya. The first land-dwelling plants developed before animals ventured onto land, with transitional species like the lobefin fish indicating a shift towards amphibious life.
Following this initial land invasion, reptiles began to dominate, laying thick-shelled eggs that prevented desiccation—a major evolutionary advantage. The role of dinosaurs emerged during this time, with their sudden disappearance around 65 mya being attributed to multiple theories, including climatic changes and evolutionary transitions into birds.
The first mammals, resembling small shrews and capable of viviparity, adapted to new ecological niches following the decline of reptiles, contributing to modern biodiversity. The gradual evolution of man, characterized by significant brain development and cultural advancements, serves as a fascinating example of evolutionary success, reflecting millions of years of adaptations and changes. Figures depicting the evolutionary timeline of major life forms highlight the interconnections among species over geological periods, illustrating the extensive span of evolutionary history.