Introduce of Amazon :
The Amazon Rainforest
also known in English as Amazonia or the
Amazon Jungle, is a moist broadleaf forest that covers most of the Amazon Basin
of South America. This basin encompasses seven million square kilometres (1.7
billion acres), of which five and a half million square kilometres (1.4 billion
acres) are covered by the rainforest. This region includes territory belonging
to nine nations. The majority of the forest is contained within Brazil, with
60% of the rainforest, followed by Peru with 13%, Colombia with 10%, and with
minor amounts in, Venezuela, Ecuador, Bolivia, Guyana, Suriname and French
Guiana. States or departments in four nations contain "Amazonas" in
their names. The Amazon represents over half of the planet's remaining
rainforests, and it comprises the largest and most species-rich tract of
tropical rainforest in the world.
History of Amazon :
The rainforest likely formed during the Eocene era. It
appeared following a global reduction of tropical temperatures when the Atlantic
Ocean had widened sufficiently to provide a warm, moist climate to the Amazon
basin. The rain forest has been in existence for at least 55 million years, and
most of the region remained free of savanna-type biomes at least until the
current ice age, when the climate was drier and savanna more widespread.
.jpg)
Following the Cretaceous,Tertiary extinction event, the
extinction of the dinosaurs and the wetter climate may have allowed the
tropical rainforest to spread out across the continent. From 65–34 Mya, the
rainforest extended as far south as 45°. Climate fluctuations during the last
34 million years have allowed savanna regions to expand into the tropics.
During the Oligocene, for example, the rainforest spanned a relatively narrow
band that lay mostly above latitude 15°N. It expanded again during the Middle
Miocene, then retracted to a mostly inland formation at the last glacial
maximum. However, the rainforest still
managed to thrive during these glacial periods, allowing for the survival and
evolution of a broad diversity of species.
During the mid-Eocene, it is believed that the drainage
basin of the Amazon was split along the middle of the continent by the Purus
Arch. Water on the eastern side flowed toward the Atlantic, while to the west
water flowed toward the Pacific across the Amazonas Basin. As the Andes
Mountains rose, however, a large basin was created that enclosed a lake; now
known as the Solimões Basin. Within the last 5–10 million years, this
accumulating water broke through the Purus Arch, joining the easterly flow
toward the Atlantic.
There is evidence that there have been significant changes
in Amazon rainforest vegetation over the last 21,000 years through the Last
Glacial Maximum (LGM) and subsequent deglaciation. Analyses of sediment
deposits from Amazon basin paleolakes and from the Amazon Fan indicate that
rainfall in the basin during the LGM was lower than for the present, and this
was almost certainly associated with reduced moist tropical vegetation cover in
the basin. There is debate, however,
over how extensive this reduction was. Some scientists argue that the
rainforest was reduced to small, isolated refugia separated by open forest and
grassland . other scientists argue that the rainforest remained largely intact
but extended less far to the north, south, and east than is seen today.This
debate has proved difficult to resolve because the practical limitations of
working in the rainforest mean that data sampling is biased away from the
center of the Amazon basin, and both explanations are reasonably well supported
by the available data.
