Travel in the Andes was extremely diffi cult and had to be
done a l most ent i rely on foot at h ig h a lt it ude s. A nde a n pe ople s
evolved large lungs and thicker blood that helped them make
the most of their oxygen-poor air. Th ey also chewed coca leaf,
a drug that helped them metabolize their food and function
better in the thin air. Th e physical diffi culty of traveling to
and from the mountains kept Andean people from trading or
engaging in cultural exchange with other South Americans.
Water shortages were a constant problem, and people devel-
oped complicated irrigation techniques to water their crops.
Th e steep slopes of the mountains made it diffi cult to grow
crops; people learned to cut terraces into the mountainsides
to create fl at fi elds.
In ancient times the mountains of the central Andes were
covered with forests. Th e trees were adapted to the climate
and altitude and included unique species, such as the queñua
and the yagual. Th e southern Andes run through modern
Argentina and Chile down to the Tierra del Fuego. Chile’s
coast contains numerous fj ords, islands, ice fi elds, and gla-
ciers. Snow cover in t his area gets progressively higher toward
the south; in the Tierra del Fuego, the snow line can be below
1,000 feet. Th e terrain and climate discouraged much human
settlement in ancient times.
Tierra del Fuego is separated from mainland South
America by a narrow strait, now called the Strait of Magellan.
Th ere appears to have been a land bridge or glacier between
the island and the mainland around 8000 b.c.e., which would
have allowed human settlers to walk there. Th e climate is cold
and stormy, and the terrain is rocky. Th e mountains feed gla-
ciers into the ocean. Only three species of trees are native to
the area. In ancient times agriculture was impossible due to
poor soil and harsh climate, so humans in this area lived by
hunting and fi shing.
AMAZON AND NORTHEASTERN SOUTH AMERICA
Th e Amazon River and its basin dominate northeastern
South America. Th e river originates in the Andes and is fed
by numerous tributaries. Most of the tributaries are diffi cult
to navigate in the mountains because of their numerous wa-
terfalls and rocky rapids. Outside of the mountains, however,
the Amazon experiences very little change of elevation along
its length, and it is fairly easy to navigate. Th e Amazon and
its tributaries were the main means of traveling through the
region before the advent of airplanes and helicopters and the
building of modern roads.
Th e Amazon is 6 miles wide in some places. About 400
miles from the ocean, it narrows to about a mile wide but
about 200 feet deep; the water fl ows very quickly there. Clos-
er to the mouth the river overfl ows its banks regularly. Th e
mouth of the river encompasses a wide area of outlets and
land about 207 miles wide. Th e Amazon does not have a delta.
A tidal bore, or wave that travels from the ocean upriver,
prevents silt from accumulating at the mouth.
Th e Amazon drains a huge area. Th e Amazon basin
contained about seven million square miles of rain forest
in ancient times. Th is rain forest was extremely dense and
diffi cult to travel through. Th e river supports a huge variety
of wildlife, including river dolphins, carnivorous piranha,
giant snakes, and a number of edible fi sh, crab, and turtle
species. Th e rain forest also harbors a plethora of species
of plant and animal, both benefi cial and dangerous to hu-
man occupants. In ancient times few people lived deep in
the rain forest. Th ose who did lived mostly as hunter-gath-
erers, though some practiced slash-and-burn agriculture, a
method of farming in which farmers cut down vegetation
and burn it to create fi elds for crops. Th e soil in most of this
region is not especially fertile and cannot sustain permanent
agriculture; the slash-and-burn technique allowed farmers
to exploit the fertility of an area and then move on to allow
it to recover over many years.
Northeast of the Amazon is the Rio São Francisco,
which was also used as a major transportation artery. South
of the Amazon the Paraná River fl ows into the Rio de la
Plata. Th e origin of the Paraná lies in the Pantanal, a giant
marshland just west of the modern southwestern border be-
tween Bolivia and Brazil. Th e Pantanal experiences annual
fl oods during the rainy season of December to May. Th is
fl ooding made the land very fertile and suitable for agricul-
ture, much as the Nile’s annual fl oods made Egyptian agri-
culture possible.SOUTHWESTERN SOUTH AMERICA
Th e Pampas is a large fertile plain encompassing nearly
300,000 square miles in modern northern Argentina and
southern Brazil. Th e name Pampas comes from a Quechua
Indian word meaning plain. Th e area was almost entirely
grassland before humans began cultivating it, but since then
it has been used very successfully for agriculture. Th e soil is
rich, and the rainfall is moderate (about 39 inches per year)
and steady throughout the year, with no particular rainy or
dry seasons, though more rain falls in summer than in win-
ter. Rainfall is heaviest in coastal areas and lighter near the
mountains to the west. Winters are cool, and summers are
warm and humid.
The landlocked Gran Chaco region lies in modern
northwestern Argentina, Paraguay, Bolivia, and a small
piece of southwestern Brazil. This area is very dry and hot.
Western Gran Chaco has almost no vegetation; in the east
the main plants are thorn bushes and grasses. The land is
almost entirely flat. Ancient humans in this region lived
as hunter-gatherers because of the difficulty of growing
anything.
Patagonia is the area encompassing the southern half
of Argentina and all of southern South America, including
some portions of the southern Andes. Most of Patagonia is
a fl at or hilly plateau, rising in abrupt terraces toward the
mountains. Th e western portions are forested with southern
beech and other deciduous trees and evergreens. Th e eastern
portion contains some rain forests and bogs in areas of high
rainfall. Eastern Patagonia is grassland. Humans lived there268 climate and geography: The Americas