Earth formed about 100 million years after the Sun, survived catastrophic impacts including one that created the moon. It lost and rebuilt its atmosphere, and cooled into fresh water oceans that made life possible. Geology didn’t merely host life, it shaped it, partnered with it, all the way to the breakup of Pangaea.
Over decades, we’ve uncovered remarkable insights into Earth’s history. The Sun ignited 4.6 billion years ago. The Earth? Rather than forming with the Sun, we now know the Earth emerged 100 million years later. This molten, chaotic sphere had a thin hydrogen and helium atmosphere that soon escaped into space. Around 4.5 billion years ago, a Mars-sized object, Theia, collided with Earth, reshaping it and forming the Moon from debris flung into orbit.
By 4.3 billion years ago, a second atmosphere of carbon dioxide, nitrogen, and water vapor enveloped the cooling planet. Volcanic activity released water vapor that condensed into the first freshwater oceans around 4.2 billion years ago. Over time, weathering added minerals, creating the salty seas we know today and setting the stage for life.
In recent decades the true role of geology emerged. Life and geology have always been intertwined. Weathering created early soils, while microbial mats transformed rocks, forging the foundation of topsoil. By 3.95 billion years ago, self-replicating molecules appeared, evolving into RNA-based life. By 3.6 billion years ago, DNA life, including LUCA—the Last Universal Common Ancestor—had emerged. Around 2.4 billion years ago, oxygen began to dominate the atmosphere, enabling the evolution of complex life forms by 1.7 billion years ago.
About 250 million years ago, the supercontinent Pangaea split apart, shaping today’s continents and ecosystems. This dramatic event also led to the distinct branches of land-locked animals we see across the globe, tying Earth’s geological changes to the evolutionary history of life.
