Early Earth
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Early Earth, also known as Proto-Earth, is loosely defined as Earth in the first one billion years — or gigayear — of its geological history, from its initial formation in the young Solar System at ab
Artist's depiction of the collision between Proto-Earth and Theia
Artist impression of the Early Earth as a lava planet during the Hadean eon
Artist's impression of Archean Earth, showing an orange atmospheric haze, leading to the alternative description of the planet in that stage of its development as a "pale orange dot"
Secondary atmosphere
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A secondary atmosphere is a planetary atmosphere that did not form directly via accretion during the formation of the planetary system. It is characteristic of terrestrial planets such as the four pla
The nitrogen-predominant (94.2%) secondary atmosphere of Titan, the largest moon of Saturn, which is denser than Earth's atmosphere