The second of three periods of the Cenozoic,
including the Paleogene, Neogene, and Quaternary, and the
second of two subperiods of the Tertiary, younger than Paleogene.
Its base is at 23.8 million years ago, and its top is at 1.8
million years ago, followed by the Quaternary period. Subdivision
of the Neogene into the Miocene, Pliocene, Pleistocene,
and Recent Epochs was proposed by Charles Lyell in 1833,
in his book Principles of Geology. The division of the Neogene
was formally proposed by R. Hornes in 1835 and
included only the older parts of Lyell’s Neogene.
The Atlantic and Indian Oceans were open in the Neogene,
and the plate mosaic looked quite similar to the modern
configuration. India had begun colliding with Asia, Australia
had already rifted and was moving away from Antarctica,
isolating Australia and leading to the development of the cold
circumpolar current and the Antarctic ice cap. Subduction
and accretion events were active along the Cordilleran margins
of North and South America. Basin and Range extension
was active, and the Columbia River basalts were erupted in
the northwestern United States. The San Andreas Fault developed
in California during subduction of the East Pacific Rise.
One of the more unusual events to mark the Neogene is
the development of up to 1.2 miles (2 km) of salt deposits
between 5.5 million and 5.3 million years ago in the Mediterranean
region. This event, known as the Messinian salt crisis,
was caused by the isolation of the Mediterranean Sea by collisional
tectonics and falling sea levels, that caused the sea to
at least partially evaporate several times during the 200,000-
year-long crisis. Rising sea level ended the Messinian crisis at
5.3 million years ago, when waters of the Atlantic rose over
the natural dam in the Strait of Gibraltar, probably forming a
spectacular waterfall.
A meteorite impact event occurred about 15 million
years ago, forming the 15-mile (24-km) wide Ries Crater near
Nordlingen, Germany. The meteorite that hit the Earth in this
event is estimated to have been one kilometer in diameter,
releasing the equivalent of a 100,000-megaton explosion.
About 55 cubic feet (155 m3) of material were displaced from
the crater, some of which formed fields of tektites, unusually
shaped melted rock that flew through the air for up to 248.5
miles (400 km) from the crater.
The Neogene saw the spread of grasses and weedy plants
across the continents, and the development of modern vertebrates.
Snakes, birds, frogs, and rats expanded their niches,
whereas the marine invertebrates experienced few changes.
Humans evolved from earlier ape-like hominids. Continental
glaciations in the Northern Hemisphere began in the Neogene
and continue to this day.
See also CENOZOIC; EVAPORITE; TERTIARY.
Tidak ada komentar:
Posting Komentar
Catatan: Hanya anggota dari blog ini yang dapat mengirim komentar.