Earth Forms
As the Sun ignited, the disc of leftover gas and dust around it began clumping together. Dust became pebbles. Pebbles became rocks. Rocks became planetesimals. And eventually, one of those growing bodies found itself at exactly the right distance from the Sun. We call it Earth.
Built from collisions
Earth formed through a process called accretion — billions of collisions over millions of years, with each impact adding more mass. Early Earth was a molten ball of rock, constantly bombarded by space debris, with no oceans, no atmosphere anything could breathe, and no land. It barely resembled the planet it would become.
The right distance
Earth sits in what astronomers call the habitable zone — the range of distances from a star where liquid water can exist on a planet's surface. Slightly closer and water evaporates. Slightly further and it freezes permanently. Earth's distance from the Sun is one of the key reasons life was possible here. Whether this was luck or whether habitable planets are common is one of the biggest open questions in science.
The invisible shield
Earth's molten iron core generates a magnetic field that extends thousands of kilometres into space. This magnetosphere deflects the solar wind — a constant stream of charged particles from the Sun that would otherwise strip away Earth's atmosphere, the way it stripped Mars bare billions of years ago. Mars lost its magnetic field, then its atmosphere, then any chance of surface life as we know it.
Layers of a world
Earth sorted itself by density as it cooled — heavy iron sank to the core, lighter rocks formed the mantle and crust. This differentiation created a geologically active planet with plate tectonics, volcanoes, and the long-term carbon cycle that regulates climate over millions of years. A geologically dead planet like Mars cannot regulate its own chemistry. Earth's internal heat is still driving the world we live on.
Earth's water did not all come from Earth itself. A significant portion — possibly most — arrived via asteroid and comet impacts during a period called the Late Heavy Bombardment, approximately 4.1 to 3.8 billion years ago. The same impacts that delivered water may also have delivered organic molecules, the chemical precursors to life. In a real sense, Earth's oceans may have fallen from space.