Scientists believe that the Earth was formed about 4.5 billion years ago. Announcing our NEW encyclopedia for Kids! If the removal of gases occurred in the solar system after nonvolatile solids had condensed but before the inner planets (Mercury, Venus, Earth, and Mars) accreted, it would have been impossible for Earth to capture a primordial atmosphere. Formation of a group of solids rich in chemically active volatiles, but not large enough to retain noble gases, followed by a loss of all materials still in the gas phase and an incorporation of the volatile-rich solids in the planet, would be consistent with the chemical evidence and with the processes described above as outgassing and importation. As radioactive potassium in rocks decayed over Earth’s history, the 40Ar produced first became trapped within mineral crystals at sites formerly occupied by K+, then was released when the crystals were melted in the course of igneous activity, and eventually reached the surface through outgassing. Therefore, even though the solar system abundance of 40Ar is much lower than that of 36Ar, its abundance on Earth is much higher because, uniquely among the noble gas isotopes listed in the table, its source—the rock-forming element potassium (K)—is part of the solid planet. There were smaller proportions of water vapour, ammonia and methane. Iron-based compounds are present in very old rocks that could only have formed if there was little or no oxygen at the time. After photosynthesizing organisms multiplied on Earth's surface and in the oceans, much of the carbon dioxide was replaced with oxygen. Sign in, choose your GCSE subjects and see content that's tailored for you. Fossils and other structural and chemical details of ancient rocks provide information useful to evolutionary biologists and historical geologists, but ancient atmospheres, “mere vapours,” have not left such substantial remnants. A thinner primordial atmosphere consisting of nebular gases with higher molecular weights (such as argon and krypton—see table), however, ought still to have been captured. Although the chemical composition of the atmosphere has changed significantly in the billions of years since its origin, the inventory of volatile elements on which it is based has not. There were smaller proportions of water vapour, ammonia and methane. For modern atmospheric chemistry and physics, see atmosphere. By signing up for this email, you are agreeing to news, offers, and information from Encyclopaedia Britannica. To the Earth scientist, the crust includes not only the top layer of solid material (soil and rocks to a depth of 6 to 70 km [4 to 44 miles], separated from the underlying mantle by differences in density and by susceptibility to surficial geologic processes) but also the hydrosphere (oceans, surface waters on land, and groundwater beneath the land surface) and the atmosphere. These molecules of gas moved so fast they escaped Earth's gravity and eventually all drifted off into space. The elemental composition of the volatile inventory reveals its secondary origin. Scientists believe that the Earth was formed about 4.5 billion years ago. As a result, a description of the history of the atmosphere must concern itself with all volatile components of the crust. While one process consumes a particular component, another produces it, and the concentration of that component in the atmosphere will rise or fall depending on the relative strengths of the sources and sinks. Depending on the question under consideration, it can make sense to speak in terms of either an ultimate source—the process that delivered a component of the volatile inventory to Earth—or an immediate source—the process that sustains the abundance of a component of the present atmosphere. Evolution of the Atmosphere. Just formed Earth: Like Earth, the hydrogen (H 2 ) and helium (He) were very warm. Which of these statements are correct about earths early atmosphere?? Iron-based. Scientists believe that the Earth was formed about 4.5 billion years ago. Interactions among these solid, liquid, and gaseous portions of the crust are so frequent and thorough that considering them separately introduces more complexities than it eliminates. Chemically active volatiles: hydrogen (H), carbon (C), nitrogen (N), oxygen (O), and sulfur (S), Elements that form nonvolatile minerals: oxygen (O), magnesium (Mg), sulfur (S), and iron (Fe).
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