The Formation of Earth

By Anya Agarwal

Edited by Naaga Senthil

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How was Earth formed? Why is Venus called Earth’s ‘Evil Sister’? What makes Mars so intriguing to scientists? These are the questions that drive exploration and discovery every day.  Our Sun emerged from a collapsing nebula, leaving behind a swirling cloud of gas and dust – a structure known as the ‘accretion disk’. Meanwhile, Earth’s formation took a different path. Atoms and molecules began to clump together, forming small particles that gradually grew into planetesimals. These rocky bodies, floating within another disk—the ‘protoplanetary disk’—collided and merged over millions of years. Eventually, after a chaotic 10-100 million years, these impacts gave rise to the planets we know today (OER Project, 2024). 

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Earth sits between two planetary neighbours: Venus and Mars. Astonishingly, 4.6 billion years ago, Earth once resembled Venus, an inferno of molten lava and relentless asteroid impacts. This then begs the question: if these planets were once so alike, why did Earth transform into a habitable paradise while Venus remained a scorching wasteland?  

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Mars, often called  the ‘Red Planet’, has been the focus of numerous NASA missions. The Perserverance rover, launched in 2020, continues to explore the Martian landscape, gathering data on rock formations and environmental conditions that might have once supported life (NASA Science, Mars- 2020 Mission Perseverance Rover, n.d.). Scientists study Mars for two key reasons: first, its ancient climate and water history may mirror Earth’s potential future; second, if Earth ever becomes uninhabitable, Mar’s might be humanity’s new home (Drake, 2015).

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Billions of years ago, Earth was unrecognizable. The Hadean Eon, named after the Greek God ruler of the underworld Hades, was a period of extreme heat and instability. With no liquid water, Earth’s surface was bombarded by radiation and cosmic debris. Asteroids and comets relentlessly crashed into the planet, generating immense heat, which was enough to keep rocks in a molten state. The surface temperature? A staggering 230°C! (Britannica, n.d.). During this time, Earth’s early atmosphere consisted primarily of methane, nitrogen and carbon dioxide. Crucially, there was no oxygen—meaning no life as we know it (Kiddle, 2023). Studying the Era helps scientists understand not only Earth’s past but also Venus’s present day conditions. Venus and Earth share striking similarities in size, mass, and density, as it is believed that both likely formed at the same time (ESA Venus Express, 2019). However, while Earth evolved into a thriving oasis, Venus remained a hostile, volcanic world. Interestingly, research suggests that microbial life could exist in Venus’s thick clouds layers, although we don’t have compelling evidence of the existence of life on Venus (NASA, 2024). 

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On the other side of Earth lies Mars, the ‘Red Planet’. Scientists have long sent rovers to its surface to seek signs of past and present life. Why Mars? Because, like Venus, it shares key characteristics with Earth. Formed from similar materials four billion years ago, Mars offers clues to planetary evolution. Understanding its surface, geological development, and history helps us answer a fundamental question: Are we alone in the universe?  

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Mars also provides a unique perspective on Earth’s own history. Evidence suggests that, at one point, Mars had abundant liquid water and a suitable atmosphere for life. However, unlike Earth, Mars underwent severe climate changes that stripped it of these resources. While life bloomed and evolved on Earth, Mars faced geological upheavals that left it barren  (The European Space Agency, n.d.). NASA’s rover Perseverance has uncovered compelling evidence of ancient Martian lakes, including a crater that was once overfilled with water. Yet today, that water is gone (Brennan, 2023). Understanding Mars’s water history may help scientists  understand how life may have survived on this once Earth-like planet. Craters, geological processes, volcanoes, and atmospheric effects all outline Mars’ history, which could help us understand Earth’s climate, atmosphere, and evolution significantly better, but also other planets in our solar system (The European Space Agency, n.d.).