"Celestial Siblings: The birth of Earth and Its Lunar Twin"
Our world began as a massive cloud of gas and dust, evolving over billions of years into the home we know today. From its chaotic beginning, Earth evolved into a world of rocky landscapes, a life-sustaining atmosphere, and enigmatic deep oceans.
Billions of years ago, our solar system was a cloud of rotating dust and gas. A cosmic event—a shockwave from a distant supernova, perhaps—a shook this cloud, and our solar system was born. This shock made dust and gas collapse inward, forming a rotating solar nebula. As the nebula cooled, its gravity pulled inward with increasing strength. The temperature and pressure at its center became so hot that hydrogen atoms fused into helium, releasing vast amounts of energy. This nuclear fusion sparked the dawn of our Sun some 4.6 billion years ago.
The newly lit Sun burned more than 99 percent of the material from the nebula, leaving the rest of the dust and gas to come together in smaller groups. These groups collided with one another and merged to form celestial bodies, including Earth. The inner planets—Mercury, Venus, Earth, and Mars—became small, rocky planets, dense enough to prevent them from being incinerated by the Sun's fiery heat.
The Early Earth and Development of Life
In its early years, Earth was a molten world dominated by volcanic activity and scorching heat. As it cooled, liquid water began to collect on its surface, forming the first oceans. Heavy elements like iron and nickel sank to the planet's center, forming a clear internal structure. The outer layer froze into a crust, and molten material accumulated at the core.
Earth's formation progressed through three main periods. First, accretion saw material in the planet accumulating gradually through repeated collisions. Second, a giant collision between a young Earth and a Mars-sized protoplanet probably created the Moon. Finally, ongoing bombardment by asteroids sculpted Earth's surface and atmosphere.
Asteroids perhaps brought life's building blocks, as well. Some contained water-rich minerals, which, when they crashed into Earth, added to Earth's reservoir of liquid water. It's estimated that almost 30 percent of water from these asteroids withstood impact, still locked up in shattered rock structures.
Throughout, Earth's early atmosphere—originally made up of hydrogen and helium—evolved through the work of volcanoes. Volcanic eruptions released water vapor, carbon dioxide, and ammonia, setting up life-supporting conditions. As Earth cooled, condensation created vast oceans, and a planet in which simple life could exist.
Photosynthetic bacteria arose about 2.7 billion years ago, harnessing sunlight to power energy and releasing oxygen. Over time, their activity transformed Earth's atmosphere, building up oxygen levels and paving the way for the complex forms of life that followed.
Today's atmosphere is about 78 percent nitrogen and 21 percent oxygen, supporting an astonishing and varied array of life. Earth's formation and evolution show us the dynamic forces that still sculpt our world—a constant evolution in the vast universe.
The Moon's Formation and Its Role in Earth's Evolution
Scientists believe Earth's history started 4.6 billion years ago in a spin-disk of gas and dust around the early Sun. Within the disk, particles collided and merged to form planetesimals that would eventually form larger planetary bodies.
The Moon likely arose 60–175 million years after the solar system formed from a gigantic impact. The impact re-melted the Earth, redistributing its metal and rock layers. Scientists measure time by analyzing hafnium and tungsten isotopes in rocks because tungsten prefers metal and would have sunk to the core after the impact.
Earth had a vast ocean of magma covering it after the impact, and only water as vapor. Strong UV radiation from the early Sun stripped away atmospheres, but volcanic activity and impacts by comets restored Earth's atmosphere. These events made way for plate tectonics, which regulate carbon dioxide and stabilize temperature, required for life.
A planet's composition, which determines whether it gets plate tectonics, is regulated by the asteroids and planetesimals that constructed it. The Moon, lacking tectonic plates, had a molten surface from the start. When it cooled, feldspar crystals rose to the surface to form the bright lunar highlands. Volcanic eruptions afterward produced dark basaltic plains, or "mare," appearing as the dark spots on the Moon. These spots, which cover 16% of the surface, formed from lava flows and are younger than the highlands.
The Moon's orbit also altered. Scientists estimate it was 17 times closer to Earth (14,000 miles) when formed compared to the distance now (250,000 miles). Its increased distance allows scientists to calibrate impact simulations more accurately to account for the Moon's chemistry and orbital history. Scientists derive the early history of Earth and how our world came to be from studying the Moon. Earth's history—how it began as a tangled cloud of dust to become a living world—is still a testament to the dynamic universe we inhabit.
