Around 4.5 to 4.0 billion years ago, what process led to a hot, molten Earth?

Around 4.5 to 4.0 billion years ago, what process led to a hot, molten Earth?

• A. Accretion of planetesimals forming a hot, molten Earth
• B. Global cooling and solidification
• C. The Moon formed from a giant impact
• D. The crust formed continents immediately

Answer: (A)

The heat that made early Earth hot and molten came from the process of accretion—the growth of the planet as countless planetesimals collided and stuck together. Each collision converts gravitational potential energy into heat, and the cumulative energy from numerous impacts was enough to melt the growing body. This melting created a global magma ocean and allowed dense materials to segregate into a metallic core and silicate mantle as the planet differentiated. Radiogenic heat from short-lived isotopes added to the warming, but the dominant factor keeping Earth molten during that time is the energy released during accretion as bodies piled up and formed the planet. The other events mentioned are related but do not explain the primary molten state on that timescale: cooling would harden the planet, the Moon-forming impact is a separate event, and crust formation after cooling does not account for the initial molten condition.

The heat that made early Earth hot and molten came from the process of accretion—the growth of the planet as countless planetesimals collided and stuck together. Each collision converts gravitational potential energy into heat, and the cumulative energy from numerous impacts was enough to melt the growing body. This melting created a global magma ocean and allowed dense materials to segregate into a metallic core and silicate mantle as the planet differentiated. Radiogenic heat from short-lived isotopes added to the warming, but the dominant factor keeping Earth molten during that time is the energy released during accretion as bodies piled up and formed the planet. The other events mentioned are related but do not explain the primary molten state on that timescale: cooling would harden the planet, the Moon-forming impact is a separate event, and crust formation after cooling does not account for the initial molten condition.