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The thermosphere contains an appreciable concentration of elemental sodium located in a 10-kilometre (6.2 mi) thick band that occurs at the edge of the mesosphere, 80 to 100 kilometres (50 to 62 mi) above Earth's surface. The sodium has an average concentration of 400,000 atoms per cubic centimeter.
The first eon in Earth's history, the Hadean, begins with the Earth's formation and is followed by the Archean eon at 3.8 Ga. [2]: 145 The oldest rocks found on Earth date to about 4.0 Ga, and the oldest detrital zircon crystals in rocks to about 4.4 Ga, [34] [35] [36] soon after the formation of the Earth's crust and the Earth
Earth's surface is the boundary between the atmosphere, and the solid Earth and oceans. Defined in this way, it has an area of about 510 million km 2 (197 million sq mi). [12] Earth can be divided into two hemispheres: by latitude into the polar Northern and Southern hemispheres; or by longitude into the continental Eastern and Western hemispheres.
c. 16th century BCE – Mesopotamian cosmology has a flat, circular Earth enclosed in a cosmic ocean. [1]c. 15th–11th century BCE – The Rigveda of Hinduism has some cosmological hymns, particularly in the late book 10, notably the Nasadiya Sukta which describes the origin of the universe, originating from the monistic Hiranyagarbha or "Golden Egg".
Earth is the only place in the universe known to harbor life, where it exists in multiple environments. [8] [9] The origin of life on Earth was at least 3.5 billion years ago, possibly as early as 3.8-4.1 billion years ago. [2] [3] [4] Since its emergence, life has persisted in several geological environments.
Cosmic Evolution — a detailed look at events from the origin of the universe to the present; Valley, John W. "A Cool Early Earth?" Scientific American. 2005 Oct:58–65. – discusses the timing of the formation of the oceans and other major events in Earth's early history. Davies, Paul. "Quantum leap of life".
This includes the effects of the solar wind, especially on the Earth's magnetosphere, ionosphere, thermosphere, and exosphere. [1] Though physically distinct, space weather is analogous to the terrestrial weather of Earth's atmosphere (troposphere and stratosphere). The term "space weather" was first used in the 1950s and popularized in the ...
The earliest life on Earth arose at least 3.5 billion years ago. [16] [17] [18] Earlier possible evidence of life includes graphite, which may have a biogenic origin, in 3.7-billion-year-old metasedimentary rocks discovered in southwestern Greenland [19] and 4.1-billion-year-old zircon grains in Western Australia. [20] [21]