How was Planet Earth Born? The 4.6 Billion Year History of Our Solar System

Around 4.6 billion years ago, the solar system didn’t exist. Instead, space was filled with a massive cloud of gas and dust called the Solar Nebula. This cloud consisted primarily of hydrogen and helium, slowly drifting in space. But everything changed when a nearby dying star exploded in a supernova.

The shockwaves from this explosion caused the nebula to collapse under its own gravity. As it condensed, the gas and dust began swirling, eventually forming a flat, rotating disk known as the protoplanetary disk. This disk is the reason why our solar system appears flat, with planets orbiting the Sun on roughly the same plane.

At the core of the disk, pressure and temperature rose dramatically. This created a protostar, the precursor to our Sun. When temperatures reached 15 million degrees Celsius, nuclear fusion began, turning hydrogen into helium and giving birth to the Sun. To this day, this reaction powers our Sun, providing heat and light to sustain life on Earth.

The remaining gas and dust in the protoplanetary disk didn’t go to waste, forming planetesimals—the building blocks of planets. Over millions of years, these collided, stuck together, and grew into protoplanets, eventually creating the eight planets in our solar system.

Earth began as one of many protoplanets, clumps of rock that collided violently during the Hadean Eon (4.6 to 4 billion years ago). These collisions generated enormous heat, melting the surface into a sea of magma. Gravity gradually shaped the Earth into a sphere, while constant impacts from asteroids and comets brought new materials—including water.

Interestingly, the water on Earth likely came from two sources: icy crystals within the solar nebula and the water trapped inside celestial bodies that collided with Earth. These collisions also released water vapor into the atmosphere, which eventually cooled and fell as rain, creating Earth’s first oceans.

Where did the Moon come from? Several theories tried to explain it, including the Capture Theory (the Moon was a wandering object caught by Earth’s gravity) and the Fission Theory (the Moon split off from Earth). However, the most widely accepted explanation today is the Giant Impact Hypothesis.

About 100 million years after the solar system formed, Earth collided with a Mars-sized protoplanet named Theia. This impact ejected a massive amount of debris, which eventually coalesced to form the Moon. Evidence for this can be found in Moon rocks collected by Apollo missions, which share chemical similarities with Earth’s rocks.

This collision also tilted Earth’s axis by 23.5 degrees, giving rise to seasons. Without this tilt, Earth’s climate would be far harsher and less conducive to life.

As Earth cooled, it started to differentiate into layers. Heavier elements like iron and nickel sank to form the core, while lighter elements like silicon and oxygen rose to the surface, forming the crust. Between the core and the crust lies the mantle, which was initially molten but later solidified in parts.

Earth’s distinct layers formed during the Archean Eon (4 to 2.5 billion years ago). The core remains searingly hot (up to 6,000°C) due to gravitational pressure and radioactive decay of elements like uranium and thorium in the mantle. The inner core is solid, while the outer core is liquid. Churning liquid iron in the outer core generates Earth’s magnetic field, vital for protecting us from harmful solar radiation.

The crust, Earth’s outermost layer, is where life thrives. It’s constantly reshaped by tectonic activity, weathering, and volcanic eruptions. Beneath the crust, high-pressure minerals like olivine and peridotite form in the mantle and occasionally erupt through volcanoes, revealing Earth’s inner secrets.