Page 47 - (DK) Ocean - The Definitive Visual Guide

THE EVOLUTION OF THE OCEANS 45

Epicontinental Seas
PEOPLE
ALFRED WEGENER At most times in the past, sea levels have been higher than they are
today. This has given rise to shallow, tideless bodies of water called
Alfred Wegener (1880–1930) was epicontinental seas covering extensive parts of the continental interiors.
a German scientist with interests
in astronomy, meteorology, and These were quite unlike the deep ocean basins and continental-shelf
geology. In 1915 he presented seas familiar to us today. The area of dry land was sometimes reduced
the theory of continental drift to to half its current extent by these seas, which were often very salty, low
explain the presence of identical in oxygen, and devoid of life. They could isolate parts of continents,
rocks on opposite sides of the causing populations of living things to evolve separately. Epicontinental
Atlantic Ocean and tropical plant seas also affected the climate: their high salinity produced downwelling
fossils in the Arctic Circle. His ideas (see p.60) of dense water into adjacent equatorial oceans, in contrast to
were not accepted until seafloor
spreading was discovered, providing the polar downwelling that dominates the deep-ocean circulation today.
a mechanism to explain his theory.
SHALLOW WATER
Conditions on the shore of North
America’s Western Interior
4. JURASSIC (150 MYA) Seaway 100 million years ago
central Atlantic
The Paleo-Tethys Sea closed as future parts of may have been similar to the
starts to open
central Asia broke away from Gondwana and shallow lagoons of the Bahama
moved north, with the Tethys Ocean opening up Islands today (right).
behind them. The central Atlantic was opening,
splitting Pangaea into northern and
southern components.
LAURASIA ASIA
NORTH EUROPE
AMERICA

PACIFIC TETHYS
OCEAN OCEAN
AFRICA
SOUTH
AMERICA
GONDWANA
AUSTRALIA
opening of north Atlantic
splits apart Europe and
ANTARCTICA North America
Western Interior
rifting signals creation Seaway ARCTIC high sea
of floor of modern OCEAN levels
Pacific Ocean polar ice cap lost
NORTH ASIA
AMERICA
EUROPE
5. CRETACEOUS (100 MYA)
The break-up of Gondwana
started with India, Africa, and PACIFIC
Antarctica rifting apart. This OCEAN
also started the closure of the AFRICA TETHYS
SOUTH
Tethys Ocean. The opening of AMERICA OCEAN
the south Atlantic soon followed,
Europe separated from North INDIA
America, and the Arctic Ocean
opened over the North Pole. AUSTRALIA
Turgai Seaway
ANTARCTICA
Gondwana
Isthmus of breaks up
Panama yet remnants of
to close
Tethys Ocean
EUROPE ASIA

ATLANTIC 6. EOCENE (50 MYA)
OCEAN India continued its rapid movement
PACIFIC AFRICA north, which would end with the uplift
OCEAN INDIA of the Himalayas when it hit Asia.
SOUTH Africa’s convergence with Europe closed
AMERICA INDIAN the western Tethys Ocean. Australia and
OCEAN South America both separated from
Antarctica, allowing the establishment of INTRODUCTION
AUSTRALIA the Circumpolar Current that isolated
Antarctica from equatorial heat flow.
Australia moves
Antarctic ice cap ANTARCTICA north
begins to form