Life on Earth began about 3.5 to 3.8 billion years ago, shortly after the planet's surface cooled enough to sustain water and carbon-based molecules, which are essential for life. Initially, Earth's surface was too hot and frequently bombarded by comets and asteroids, preventing life from forming. The impacts of comets and asteroids likely delivered water and organic molecules necessary for the building blocks of life. The earliest life forms were microscopic, single-celled organisms capable of self-replication, possibly using DNA, RNA, or other molecules. These early organisms thrived in environments such as shallow ponds, hot springs, or hydrothermal vent areas on the ocean floor, where chemical reactions fueled by heat and energy sources allowed life to emerge. One possible spark for life's chemical beginnings could have been lightning strikes that created reactive molecules in the atmosphere. Life developed from these simple organisms into more complex forms over time, with cyanobacteria emerging around 2.4 billion years ago, producing oxygen and changing Earth's atmosphere, setting the stage for the evolution of animals and more complex ecosystems. The emergence of life involved a combination of chemical, geological, and possibly extraterrestrial factors working together in Earth's early environment.