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The geological time scale is divided into Eras which has the longest span which is further divided into periods and the periods are divided into Epochs. Understanding the Pre-Cambrian era and subsequent geological periods is crucial for comprehending Earth's evolutionary history, the formation of landforms, and the development of life on our planet. PRE-CAMBRIAN ERA Archeozoic Era The Archeozoic Era started 3.8K-600 million years ago . Earth was very hot & had violent volcanic Eruptions . Proterozoic Era Started 2K million Years ago (MYA) . It is also known as pre-cambrian era . The world's oldest fold mountain Aravalli belongs to the pre-cambrian era. PALEOZOIC ERA Overview Started around 600 MYA . It is divided into 6 periods . Life started originating in the pre-cambrian era. Cambrian Period This was the earliest period in which majority of the oceans were flo...

The Plate Tectonic Theory is a major theory in global tectonic system that revolutionized our understanding of Earth's dynamic processes. This comprehensive theory explains the formation of mountains, occurrence of earthquakes and volcanoes, and the continuous movement of continents. It represents a significant advancement influenced by quantitative revolution, positivism, and system analysis in physical geography. What is Plate Tectonic Theory? The Plate Tectonic Theory (PTT) is a major theory in global tectonic system influenced by quantitative revolution, positivism, and system analysis in physical geography. The term "plate" was given by Wilson, Morgan, and Mackenzie . The plates are solid lithospheric slabs which slide on elastic/plastic asthenosphere . Lithosphere = Crust + Upper Mantle These plates experience continuous horizontal and vertical movement which causes deformation of rock on the Earth's crust or crustal ...

The Sea Floor Spreading Theory explains how the ocean floor is formed and changes over time. According to this theory, new oceanic crust is created at mid-oceanic ridges and old crust is destroyed at trenches. This process works like a moving conveyor belt and helps us understand the movement of plates and changes on the Earth’s surface. BACKGROUND During the exploration of the ocean floor during World War II , a large amount of evidence was found regarding the presence of different relief features under the oceans. It was also observed that the temperature is high around a continuous mountain system, known as Mid-Oceanic Ridges . BASIC INTRODUCTION During World War II, sonar radiation was used to map the ocean floor, and magnetic anomalies were also studied. It was found that the ideal ocean floor has certain features, as shown in the diagram below:- → Thus, Harry Hess gave his Sea Floor Spreading Theory in 1960 . According to h...

The formation of fold mountains has been explained through various theories, with the Geosyncline theory being one of the most significant early attempts. This theory provides insight into how long, narrow depressions filled with sediments eventually transform into towering mountain ranges through processes of sedimentation, subsidence, and compression over geological time periods. What is Geosyncline? The long, narrow, and shallow depression characterized by sedimentation and subsidence is defined as the geosyncline . Geosyncline lies between two stable blocks, and these blocks move toward each other due to the subsidence of the floor of geosyncline caused due to the sedimentation of these blocks. Such blocks are known as Foreland . Geosyncline theory explains the formation of fold mountains . The concept of geosyncline was given by Hall and Dana , and it was further developed by Steers . CHARACTERISTICS OF GEOSYNCLINE According to Hall...

The Convectional Current Theory was proposed by Arthur Holmes in 1928 to explain the driving force behind continental movement and mountain building. According to this theory, convection currents operating within the Earth's mantle are responsible for the movement of continents, the formation of oceans, and the origin of fold mountains. MECHANISM OF THE THEORY → Convection currents are generated deep inside the mantle due to the radioactive decay of elements in rocks , causing very high temperatures. This leads to the development of convectional currents, which start rising upward . → When the convectional currents reach the crust, they diverge in different directions , stretching the crust and creating seas and oceans. The oceanic crust being thin, is easily broken; therefore, sea-floor spreading occurs.Holmes stated that this is how the Tethys Sea was formed between Pangaea and Gondwana . → According to Holmes, the crust in the equato...

The theory of Isostasy explains the gravitational equilibrium between different relief features on Earth's surface. This fundamental concept helps us understand why mountains, plateaus, and ocean basins maintain a state of balance despite their varying heights and masses. The study of isostasy is crucial for understanding Earth's crustal structure and dynamics. THEORY OF ISOSTASY Introduction There are different physical features such as mountains, plateaus, and plains on the surface of the Earth which vary greatly in size. Despite this variation, these features are balanced or are in equilibrium. The study of equilibrium or the state of balance between the upstanding part and the low-lying basin is known as the state of Isostasy . The term was first given by "Dutton" to determine the state of gravitational equilibrium between the different relief features on the rotating Earth. According to Dutton, the higher features such as m...

The permanency of position has been challenged by major theories such as continental drift theory, sea floor spreading theory and other theories of landform development. These theories help us understand the dynamic nature of Earth's surface and explain various geological phenomena observed across the globe. INITIAL OBSERVATIONS Distribution of Landmass and Water Bodies There is more concentration of landmass in the northern hemisphere (approximately 75% of landmass ) while there is more concentration of water in the southern hemisphere. Shape of Continents Except for Australia and Antarctica , most of the continents are roughly triangular in shape . Similarly, the majority of oceans are also triangular in shape . Antipodal Arrangement The triangles are arranged in such a manner that for the continents the base is to the north and apex is to the south , while for the oceans the base is to the south and apex is to the n...