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Why did early Earth need more carbon dioxide to keep its oceans liquid?

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Wispy cirrus clouds stretch across a bright blue sky above trees and a river at Pinawa Dam Provincial Park in Manitoba, Canada, with sunlight illuminating the scene. — Atmosphere The atmospheres of planets in the solar system are composed of various gases, particulates, and liquids. They are also dynamic places that redistribute heat and other forms of energy. On Earth, the atmosphere provides critical ingredients for living things. Here, feathery cirrus clouds drift across the deep blue sky over Pinawa Dam Provincial Park, near Pinawa, Manitoba, Canada.

Early Earth required higher concentrations of carbon dioxide to maintain liquid oceans due to the "faint young Sun paradox." During Earth's early history, the Sun emitted significantly less solar radiation than it does today.1

Without an enhanced greenhouse effect to trap heat, the planet's surface temperatures would have been low enough for all surface water to freeze solid. High levels of atmospheric carbon dioxide—estimated to have been up to 100 times greater than current levels—provided the necessary warming to keep the oceans in a liquid state despite the lower solar output. As the Sun's luminosity gradually increased over geologic time, these greenhouse gas concentrations were regulated and reduced through processes such as rock weathering and biological activity.123