Physical Geography

What is the Theory of Seafloor Spreading? The theory of seafloor spreading was first proposed by Harold Hemmond Hess in 1960. the two fundamental facts that led him to postulate theory are: (i) the mid-ocean ridge occurs in all major ocean basins, and (ii) the oceanic crust has a thickness of 6 to 7 kilometers only whereas the typical thickness of continental crust is 30-40 km. Hess postulated that the […]

The flow of high heat associated with oceanic ridges proves the existence of “Convection Currents in the Mantle”. These currents are believed to be responsible for the movement of crustal plates. The idea of convection currents was first suggested by a British geologist A. Holmes in 1927 when he tried to explain the driving mechanism for continental drift. Holmes proposed that sub-crustal convection currents dragged the two halves of the […]

The theory of Plate Tectonics has evolved from Harry Hess’s concept of “seafloor spreading”. He proposed this concept in the early 1960s. Hess’s hypothesis was accepted when Vine and Mathews used it in explaining linear magnetic anomalies of the ocean basins. In 1967, W. J. Morgan, and J. T. Wilson extended the idea of Hess and produced the theory of plate tectonics. The factors, which led to the theory of […]

The theory of continental drift was presented by a German geologist, Alfred Wegener in 1910. He suggested that at the beginning of the Mesozoic era (200 million years ago), all the continents of the earth were united together. These continents were united to form a single supercontinent, which he called “Pangaea”. The huge ocean, that surrounded it, he called “Panthalassa”. Wegener proposed that this vast continent began to break up into […]

Isostasy C.E Dutton, in 1889, suggested that a gravitational balance exists between the elevated masses (i.e. continents) and ocean basin of the earth’s crust. It is believed that the lithosphere floats on the top of the partially molten substratum (asthenosphere) much like logs float on water. Mountains stand high because they are composed of rocks of low density, and ocean basins are low because they are made up of rocks […]

The mantle is a layered part of the earth, which is located just beneath the crustal layer of the earth. The Earth’s crustal surface (lithosphere) rides atop the asthenosphere. The asthenosphere is the upper layer of the Earth’s mantle, in which there is relatively low resistance to plastic flow and convection is thought to occur. While the lower part of the mantle is very hot and molten. Mantle convection means the movement […]

The knowledge about the interior structure and composition of the earth has a long history. Before seismic tomography, scientists knew very little about the interior of the earth. The study of the passage of seismic waves through the earth has helped in knowing the structure of the earth’s interior and in defining the physical properties of various layers. The seismic waves travel at different velocities depending on the nature of […]

What is radioactive decay? Radioactive elements continuously release their protons and neutrons and form new daughter products. The radioactive elements are often known as the “parent”, and the element resulting from the decay is known as the “daughter product”. As the number of protons and neutrons is different in parent and daughter products, therefore the daughter product becomes a quite different element. This process is known as radioactive decay, and […]

Physical Geography Definition Before going to the definition of physical geography, let’s have a brief introduction to Geography and its branches. Geography is a branch of natural science, devoted to the study of the lands, features, inhabitants, and phenomena of Earth. Geography is an all-encompassing discipline that seeks an understanding of Earth and its human and natural complexities—not merely where objects are, but also how they have changed and come […]

Age of the Earth The age of the Earth as determined by the current method of radiometric dating is about 4600 million years. Before the discovery of radiometric dating, several attempts were made to determine the age of the Earth. The important ones are as follows. From the discovery of organic evolution From the rate of sedimentation From the salinity of seawater From the rate of cooling From the history […]