Biosphere Evolution: How Life Changes Planets Over Time

The story of life on Earth begins over 4 billion years ago, during a period when the planet was vastly different from what we know today. The early Earth was a hostile and volatile environment, shaped by intense volcanic activity, frequent meteorite impacts, and a lack of atmospheric oxygen. Despite these harsh conditions, it provided the chemical and physical building blocks necessary for life to emerge. Scientists believe that simple organic molecules formed in Earth’s primordial soup, potentially aided by energy sources such as lightning or hydrothermal vents. These molecules eventually combined into more complex structures, leading to the first self-replicating systems and, ultimately, the first living organisms.

The earliest known life forms were microscopic, single-celled organisms, likely similar to modern-day archaea and bacteria. Fossil evidence suggests that these microbial communities were thriving as early as 3.5 billion years ago. These organisms did not rely on oxygen but instead used anaerobic processes to generate energy. Some may have metabolized sulfur or iron, contributing to chemical changes in the oceans and atmosphere. Their interactions with their environment began the long process of transforming Earth from a lifeless rock into a living world.

The early biosphere—composed of these primitive life forms—played a pivotal role in shaping planetary systems. As life grew more complex and abundant, it started to influence global processes such as the cycling of carbon and the formation of sediments. Microbial mats, for instance, trapped particles and created layered structures known as stromatolites, which are among the oldest evidence of life on Earth. These biological structures began to interact with the geosphere, setting the stage for future planetary changes.