According to scientific theory, life began through abiogenesis, in which non-living matter gradually formed complex organic molecules such as amino acids and nucleotides, which then combined into simple cellular structures (prokaryotes) around 3.7–4 billion years ago, under conditions on a primordial Earth rich in methane, ammonia, hydrogen, and water vapor, as well as energy from lightning. Modern theory explains the transition from chemistry to biology through several hypotheses, such as the RNA World or metabolism-first, which focus on the spontaneous synthesis of the building blocks of life.
Early Life Processes (Abiogenesis) :
Primordial Earth: The early atmosphere was rich in methane, ammonia, hydrogen, and water vapor, and energy from lightning created organic compounds such as amino acids and nucleotides.
Formation of Complex Molecules: Amino acids combined to form proteins, and lipids formed membrane-like structures (protocells) that isolated molecules.
The RNA World: RNA is thought to be the earliest genetic information molecule due to its ability to store information and catalyze reactions, before DNA took over these roles.
First cells: Simple prokaryotic organisms emerged, utilizing chemical energy sources such as sulfur and nitrogen, and later evolving using carbon dioxide.
Eukaryotes: Thought to have arisen through endosymbiosis, where larger prokaryotic cells engulfed smaller ones, becoming organelles such as mitochondria and chloroplasts.