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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 itself.
Mesopotamian cities became self-run civil governments. One of the cities within this civilization, Ur , was the first literate society in history. Eventually, they constructed irrigation systems to exploit the two rivers, transforming their dry land into an agriculturally productive area, allowing population growth throughout the cities and ...
Generally, the age is estimated based primarily upon the age of any mountains it dissects; the age of the sea or ocean to which it eventually outflows can be irrelevant; for example, several rivers of the east side of the Appalachian Mountains are thought to be older than the Atlantic Ocean into which they flow. If a river fully dissects a ...
The mass of Earth's oceans is estimated to be 1.37 × 10 21 kg, which is 0.023% of the total mass of Earth, 6.0 × 10 24 kg. An additional 5.0 × 10 20 kg of water is estimated to exist in ice, lakes, rivers, groundwater, and atmospheric water vapor. [20] A significant amount of water is also stored in Earth's crust, mantle, and core.
So to understand how we came to exist on planet Earth, we'll need to know how Earth managed to stay fit for life for billions of years. Earth has been habitable for billions of years ...
The latter two are sub-divided into several eras as currently defined. In total, the Precambrian comprises some 85% of geological time from the formation of Earth to the time when creatures first developed exoskeletons (i.e., hard outer parts) and thereby left abundant fossil remains.
The Clean Air Act is passed in the United States, with subsequent amendments in 1970, 1977 and 1990. 1974 World population reached 4 billion. [23] 1970s 2010s Deindustrialization occurs in the Midwest and then much of the United States, as manufacturing industries (and their pollution) move to China and other Asian countries. 1980
While they were sailing west around the Southern tip of Africa, it was found that the Sun was to their right (the north). This is thought to have been a key trigger in the realization that the Earth is spherical, in the classical world. In the 4th century BC the Greek explorer Pytheas traveled through northeast Europe, and circled the British ...