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Oxygen is the third most abundant chemical element in the universe, after hydrogen and helium. [68] About 0.9% of the Sun 's mass is oxygen. [ 19 ] Oxygen constitutes 49.2% of the Earth's crust by mass [ 69 ] as part of oxide compounds such as silicon dioxide and is the most abundant element by mass in the Earth's crust .
The troposphere is the lowest layer of Earth's atmosphere. It extends from Earth's surface to an average height of about 12 km (7.5 mi; 39,000 ft), although this altitude varies from about 9 km (5.6 mi; 30,000 ft) at the geographic poles to 17 km (11 mi; 56,000 ft) at the Equator, [22] with some variation due
Although oxygen is the most abundant element in Earth's crust, due to its high reactivity it mostly exists in compound forms such as water, carbon dioxide, iron oxides and silicates. Before photosynthesis evolved, Earth's atmosphere had no free diatomic elemental oxygen (O 2). [2]
Silicon is a bioessential element and is one of the most abundant elements on Earth. [61] [62] The silica cycle has significant overlap with the carbon cycle (see the carbonate–silicate cycle) and plays an important role in the sequestration of carbon through continental weathering, biogenic export and burial as oozes on geologic timescales. [63]
Most of Earth's surface is ocean water: 70.8% or 361 million km 2 (139 million sq mi). [96] This vast pool of salty water is often called the world ocean, [97] [98] and makes Earth with its dynamic hydrosphere a water world [99] [100] or ocean world. [101] [102] Indeed, in Earth's early history the ocean may have covered Earth completely. [103]
Iron is the most abundant element by mass in the Earth, but most of it is locked up in the Earth’s core, 1,800 miles beneath our feet, Wade said. Despite this, life forms rely on iron for survival.
The Earth's crust is one "reservoir" for measurements of abundance. A reservoir is any large body to be studied as unit, like the ocean, atmosphere, mantle or crust. Different reservoirs may have different relative amounts of each element due to different chemical or mechanical processes involved in the creation of the reservoir. [1]: 18
Hydrogen is the most abundant element to the universe—it's actually element number one—and the atomic weight is 1.008, so 10/08 is designated National Hydrogen and Fuel Cell day, because many ...