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Some scientists state that ice delivered by comet impacts could have supplied the planet with additional water vapour. It is generally thought that ammonia, methane, and neon were present sometime after the crust cooled, and volcanic outgassing added water vapour, nitrogen, and additional hydrogen. The early atmosphere likely began as a region of escaping hydrogen and helium. Although many scientists contend that the atmosphere and the oceans formed during the latter part of the eon, the discovery of the zircon grains in Australia provide compelling evidence that the atmosphere and ocean formed before 4.4 billion years ago. The oldest minerals are the aforementioned grains of zircon, which were found in the Jack Hills of Australia.Д¬onsiderable debate surrounds the timing of the formation of the atmosphere as well as its initial composition. The oldest rocks known are the faux amphibolite volcanic deposits of the Nuvvuagittuq greenstone belt in Quebec, Canada they are estimated to be 4.28 billion years old. Since Hadean times, nearly all of this original crust has subducted from the movements of tectonic plates, and thus few rocks and minerals remain from the interval. Although no one knows when the first outer crust of the planet formed, some scientists believe that the existence of a few grains of zircon dated to about 4.4 billion years ago confirm the presence of stable continents, liquid water, and surface temperatures that were probably less than 100 вЊ (212 вЏ). Heavier elements, such as iron, descended to become the core, whereas lighter elements, such as silicon, rose and became incorporated into the growing crust. Convection currents in the mantle brought molten rock to the surface and caused cooling rock to descend into magmatic seas. EncyclopГ¦dia Britannica, Inc./Christine McCabeД®arthвЂ™s surface was incredibly unstable during the early part of the Hadean Eon. Several of Earth's most significant moments occurred during the planet's first 600 million years.

SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents EarthвЂ™s To-Do List for the 21st Century.Britannica Beyond WeвЂ™ve created a new place where questions are at the center of learning.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.

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COVID-19 Portal While this global health crisis continues to evolve, it can be useful to look to past pandemics to better understand how to respond today.Student Portal Britannica is the ultimate student resource for key school subjects like history, government, literature, and more.From tech to household and wellness products. This Time in History In these videos, find out what happened this month (or any month!) in history.#WTFact Videos In #WTFact Britannica shares some of the most bizarre facts we can find.Demystified Videos In Demystified, Britannica has all the answers to your burning questions.Britannica Explains In these videos, Britannica explains a variety of topics and answers frequently asked questions.

Britannica Classics Check out these retro videos from Encyclopedia BritannicaвЂ™s archives.