2.0 THE FORMATION OF CONTINENTS
THE FORMATION OF CONTINENTS
The formation of continents is one of import part which should be covered on this topic.
Since may time ago many questions have bewn posed from different angles concerning
the formation of continent hence this issue has become as controversial, therefore
different scholars have tried to elaborate this issue by developing their theories which
were supported by evidences. However the formation of continent is discussed by the
following theories:-
a. Continental drift theory.
b. Plate tectonic theory.
c. The sea floor spreading.
A. CONTINETAL DRIFT THEORY
This theory was first proposed by some scientists like Francis Bacon in 1620 and F. B.
Tylor who postulated about horizonatal displacement of the continents and distribution
of fold mountains who explained about the horizontal displacement of continents on
explaining the distribution of fold mountains. but later on was advanced by Alfred
Wagner to be the new version by the 1912. The theory argued that, about 280 million
years ago, the present continents were united in the single landmass called PANGAEA
which surrounded by the ocean called Panthlassa. About 200 million years ago due to
the presence of different forces acted on this Pangaea (single land mass) was broken
up in two parts which were northern part and southern part, the northern part was called
Laurasia while the southern part was called Gondwanaland, these two continents were
separated by long narrow sea called Tethys. About 150 million years ago due to the
continuous forces the Laurasia (Northern part) and the Gondwanaland (Southern part)
were further broken up to produce the present seven continents. However the Eurasia
produced (North America, Europe and Asia) while Gondwanaland was formed (South
America, Africa, Australia, Antarctica and New Zealand).
According to Wegner the forces caused the continental drift include
i. Centrifugal forces: Is the forces caused by the earth rotation. Therefore the earth
rotation cause continents to move slowly. Therefore the centrifugal forces caused the
continents to break apart
ii. Tidal attraction: Wegner explain that tidal influence the moon and the sun attraction
to be attracted and form continents westward.
EVIDENCES WHICH SUPPORT THE CONTINENTAL DRIFT THEORY
EVIDENCES WHICH SUPPORT THE CONTINENTAL DRIFT THEORY
Alfred Wegner proposed the number of evidences to support the theory and to make
people to believe on it. Therefore the theory was supported by the following evidences:-
1. The jig-saw fit: According to Wegner, by looking the appearance of the continents
there is possibility of one continent to fit in to another, and can therefore it is possible
all continents to unite and form the single landmass (Pangaea) again. Example: South
8
Side the Great 0717435890
America could fit to Africa, North America could fit to Europe and Australia could fit in
Asia.
2. Geological evidences: This evidence based on critical studying and making
comparison on rocks found in different contintinents. According to Wegner some rocks
found in different continents have the same age, structure and resistance. Therefore
these rocks suggest that they were formed together before shifting of continents.
Example the rocks found in west African coasts look similar to that found in south
American coasts specifically in Brazil interms of their age, structures, minerals
composition, permeability and resistance.
3. Biological/paleontological evidences: The theory suggests that, there are some plant
and animal species (Fauna and Flora) in some continents which look similar with those
from other continents. However the theory suggest that those organisms were shifted
with continents during the drifting period. Example fossils of Mosasaurs, a freshwater
reptiles, has been found both in Brazil and in west Africa. Also fossils of the land
reptiles Lystrousarus have been found in rock of the same age in Africa, India and
Antarctica. However also there is distribution of glossopteris flora in India, South Africa,
Australia, Antarctica, Falkland island. Therefore all these species prove that the
continents were shifted from the single landmass.
4. Geomorphological evidences: According to Wenger the existence of fold mountains
with similar physical characteristics like origin, age and rock structure in different
continents in the world suggest that these mountains were formed together before the
shifting of continents. Example Atlas mountain in North Africa (Morocco) and Alps
mountain in cental Europe suggest that these mountains were formed together during
the time when the continents were single landmass since they have the same age and
rocks characteristics.
5. Glaciation evidence: The theory show that, there are some parts of the world with
glacial deposits even though some area there is hot climate. The theory argue that
during the drifting some continets were drifted from the polar regions with low
tempreature example antarctica. Example presence of glacial deposts in congo basin
indicate that Congo as a part of African continent was shifted from the areas with ice
sheet (low temperature) in southern hemisphere because about 300 million years ago
the whole part of southern hemisphere were occupied by ice. Moreover there is
existence of coals in Britain indicate that these coals was deposited from the areas with
warm climate about 300 million years ago. By that time continents were still united.
6. Existence of rift valleys: The theory suggest that the existence rift valleys in different
parts of the worlds suggest that drifting has occurred and this rift valleys were formed
due to movement of plates beneath the continents. Example of great rift valley in east
9
Side the Great 0717435890
Africa which started from the middle east run through Nubia and Sudan to east African
countries specifically (Lake Trukana (Kenya), Tanzania to Zambia.
7. Paleomagnetism: Wegner agues that the large scale plate motion were derived from
the studies of different aspects of magnetic fields. Wegner argue that when the rock
cooled, they were magnetize in the same direction where the magnetic fields were
found. The shifting of continent is detected by using instrument called Magnetometer.
Which is based on determining the rock magnetic fields.
8. The red sea evidence: The Red sea started as a rift valley in about 20 millions years
ago. However nowadays Red sea has about 300km wide. Red sea was formed by
divergence between African continent (plane) and Arabian plate.
EFFECTS OF CONTINENTAL DRIFTING
1. Formation of physical features: Continental drifts contributed to the emergence of
some features like mountains, riftvally and sea. Example Atlas mountain in Morocco
(Both Africa), Alps mountain in central Europe.
2. Climate change: The theory argue that continental drifting contributed to the change
in weather condition like temperature, wind rainfall and other weather variable due to
the fact that some continents were shifted to the polar regions.
3. Change in ocean current patterns: The continental drifting in some continents has
changed the condition of oceanic circulation by affecting the temperature conditions.
Example the water around New Zealand’s south island cooled from 20°c to about 56-53
million years to about 17°c during 30-14 millions years ago.
4. Evolution of animals species: The Continental drifts contributed to change in plant
and animal species. The shifting of continents has contributed to changing in plant and
animal species due to the influence of physical environment.
5. Crustal deformation: Normally the shifting of continents has been considered as the
main source of crustal catastrophe like earthquake, vulcanism and tsunami.
6. Variation in some human activities: Due to changing in global geographical location
has lead to the variation of some human activities which depend from the climatic
regions.
WEAKNESS/LIMITATIONS/ SHORTCOMINGS/CRITQUES FOR THE THEORY
QN: The Continental drift theory is irrelevant to Tanzanian society. Discuss this
statement by giving five (5) points.
10
Side the Great 0717435890
1. The theory failed to explain the true mechanisms used to divude and drive
continents: Because the centrifugal forces created by the earth rotation according to
scientists is unable to drift continents. Moreover the tidal attraction cannot able to squiz
continents.
2. The theory failed to explain the formation of glaciers in hot climatic condition such as
in Iran’s hot desert.
3. With respect to jig saw fit, not all continents could able to fit between one another.
4. The occurrence of plant species may be spread by the influence of water and wind.
5. Moreover, Wegener face critiques that, he was a geologist but he was not
meteorologist.
IMPORTANCE OF CONTINENTAL DRIFT THEORY
QN: The Continental drift theory is relevant to Tanzanian society. Discuss this
statement by giving six points.
1. The theory helps in explaining the reasons behind the formation of continents.
2. The theory help to promote critical thinking to the learners on geological studies.
3. The theory help on describing the causes of different landforms like rift valleys,
mountains, basins and other landforms in different parts of the world.
4. The theory helps in critical studying the distribution of biodiversity in the world in both
plant and animals).
5. The theory provide guidelines on determining forces which affects the planet earth.
6.The theory help to predict the future dynamic phenomena on the planet earth example
formation rift valleys.
7. The theory helps in studying the distribution of earth quakes and volcanic activities
on the planet earth.