Introduction
Questions regarding what the Earth is, how it started, how it operates and possible changes have been explored by some of the brightest scientists of the centuries. While remarkable achievements have been made in explaining the science behind the formation and mapping of the Earth, some major issues are yet to be fully understood. It does appear that discoveries often lead to new questions about the Earth. Nevertheless, this paper aims to provide history, main theories, and theorists involved in the formation and mapping of the Earth. Thus, it provides sufficient reliable information and explanation under the history, formation, and mapping of the Earth.
History
During the period of antiquity, the first geologists generally concentrated on the origin of the Earth. Specifically, earlier geological thoughts about the origin of the Earth emanated from Ancient Greece. In the 4th century BC, Aristotle noted some significant observations (Gohau, 1990). The scholar observed a sluggish geological transformation. He noted elements that constituted the land and developed a theory that claimed that the Earth transformed at an extremely slow pace, and it was impossible to note these transformations during one’s lifetime. Aristotle was among the first scholars who developed evidence-based concepts related to the geological scope about the pace at which the Earth physically transformed.
After the work of Aristotle, Lyceum presented a more progressive work focusing on stones – minerals and ores obtained from various locations. Lyceum described various rocks and classified them based on some properties such as hardness (Gohau, 1990). Later in the Roman period, Pliny observed other metals and minerals and pioneered crystallography.
In the middle ages, more works appeared. Abu al-Rayhan al-Biruni (AD 973-1048) claimed that the Indian subcontinent was initially a sea. Ibn Sina (Avicenna, 981-1037), Ikhwan AI-Safa, and many others further focused on the earlier works of Aristotle in which they discussed the formation of mountains and minerals, water sources, cloud formation, earthquakes, and variations in the Earth’s terrains among others. Shen Kuo, a Chinese naturalist, developed several theories, including geomorphology based on the assessment of sedimentary rocks, soil erosion, uplift, silt, and marine fossils. Kuo also proposed the theory of slow climate change following a study of petrified bamboos. Further, he developed a hypothesis to support land formation from activities involving mountain erosion and silt deposit after studying fossil shells.
In the 17th century, major works concerning the Earth were based on the Bible, for instance, William Whiston strived to confirm that the Great Flood had indeed taken place (Gohau, 1990). Consequently, the Flood led to the discovery of fossils and using Christian argument to demonstrate that it was responsible for the development of the Earth’s rock strata (Gohau, 1990). Conflicts between science and religion on the origin of the Earth also emerged during this period. Geology also became a distinct discipline in this era (Leddra, 2010).
Events of the 19th century, including the Industrial Revolution and the mining industry, were responsible for increased interests in sequences of rock formation based on the order of the period of formation – stratigraphic column. William Smith from England and Charles Darwin showed the significance of fossils in understanding landscape formation. Darwin further advanced the idea of an expanding and sinking Earth to create the land and ocean. Events that followed later allowed geologists to measure the age of the Earth.
Until only lately after thorough research, geologists had not noted that the Earth’s surface had not transformed much since it formed more than 4.6 billion years ago (Dalrymple, 2001). Specifically, the Earth’s history concentrates on transformations that have taken place since its formation to the present day. Almost all fields of natural science have conducted significant studies to contribute to the comprehension of the major events of the history of the Earth. The age of the Earth is estimated to be about a third of the age of the universe. Critical amounts of geological transformations have taken place since the Earth’s formation.
Scientists have strived to show that the Earth was formed from lump from the solar nebula. Volcanic outgassing perhaps was responsible for the elemental condition and then the ocean. However, there was limited oxygen in the atmosphere to support modern life. It is further observed that much of the Earth was once in a molten status due to many collisions with other bodies witnessed. This situation resulted in extreme volcanism (Kokubo & Ida, 2002). Consequently, a major impact collision with a similar size as the planet is believed to be responsible for the formation of the Moon. For periods, the Earth cooled, resulting in the development of solid crust that subsequently carried water. Today, there are oceanic crust and continental crust. An oceanic crust forms part of the ocean bed.
Studies and Theories
Since the 1800s, scientists have conducted multiple studies to understand the Earth’s formation and mapping. As previously noted, most scholars observed that the Earth could have cooled after its formation. The surface was subjected to intense heat from the sun over time and it contracted and dried to represent some of the transformation, movements, and realignments that could have transpired over millions of years.
Contraction Theory
Some leading researchers advanced this theory in the late 1800s and the early period of 1900s (Egger, 2003). The contraction theory claims that some mountain ranges, such as the Himalayas were consolidated during the contraction process ( Pennsylvania State University, 2014). According to this theory, all elements found on the Earth had formed during a single cooling period, and that the Earth was comparatively static with minimal changes as cooling declined to an end more than millions of years ago.
The Continental Drift Theory
Some scientists were however not convinced by the contraction theory. In fact, in the 1900s, Alfred Wegener, a German scientist, noted some interesting features (Egger, 2003). The same fossils of animals and plants were both found in South America and Africa and on other continents as well. However, these continents were widely separated by huge oceans. He also noticed that the same rock formations also appeared in different distant continents. Consequently, Wegener argued that these pieces of formations were once a block but later drifted. The scientist based the theory on the jigsaw puzzle pieces, which showed that some continents indeed appeared to join well at the edges (Egger, 2003). Further, Wegener collected available data on paleoclimate (data studied from rocks to reflect past geologic climate) from various continents. Belts of coal associated with tropical regions were present across Europe, North America, and Asia. The current topics are wide apart. An ice sheet was also traced from southern Africa to India. These are phenomena, which are difficult to account for based on the current positions of different continents. Based on these observations, Wegener’s theory asserted that all of the continents had initially been a single piece of a supercontinent referred to as Pangaea. This was about some 300 to 360 million years ago, but after some 50 million years ago, the drift occurred, resulting in widespread distribution of species. These species could have not migrated to other continents across oceans.
However, critics continued to ridicule the theory that claimed that the continents had moved. Wegener had failed to explain possible forces that could have caused the drift. The driving force behind the movement of the continents was extremely important to theory. The theorist based his observations on information obtained from the continents’ jigsaw puzzle, fossil, and rock evidence, but not the oceans, which cover about 70% of the Earth.
Mapping
The first and second World Wars introduced new eras of scientific and technical achievements. Before then, many geologists believed that the ocean bed was flat and featureless. Geologists could map the ocean bed and evaluate its magnetism using ships installed with sonar. Consequently, in the 1950s and 1960s, Henry Menard, Marie Tharp, and Bruce Heezen, marine geologists, used data collected from the seabed to demonstrate the presence of ocean ridges found in the Pacific and North Atlantic (Egger, 2003). The data showed that the ridges were more than thousands of kilometers long and appeared as long mountains stretched throughout the Earth. They also concluded that ridge crests consisted of topography that was similar to volcanic rift zones observed on land, and crests were V-shaped valleys. Consequently, in 1962, Harry Hess, American geologist argued that the mid-ocean ridges were the location in which hot magma had risen close to the Earth’s surface, pushing the ocean floor away. Subduction zones were formed, which forced the ocean floor to spread deeper in some regions, such as Japan and South America’s coastal regions. Consequently, the theory of seafloor spreading provided by Hess also explained Wegener’s theory of Continental Drift, but more evidence was still required.
Another American petrologist, Robert Dietz and Geodetic Survey (the federal department that made maps) also observed the seafloor rocks had created an alternative striped seafloor rock feature (Woods Hole Oceanographic Institution, 2005). The magnetometer data further revealed how the alternating strip emerged between rocks with a magnetic field and other rocks (Woods Hole Oceanographic Institution, 2005). It is also observed that the subduction zones are known for rampant volcanoes and earthquakes. These phenomena occur at the edges of the continents. For instance, the Rim of Fire derives its name from earthquakes and volcanoes common along the coastline of the Pacific Ocean, notably in Central America, western sections of South America, and Alaska islands. It also spreads to Japan, New Zealand, and the Philippines, which are western Pacific regions.
The Theory of Plate Tectonics
Since geologists wanted a better explanation for the continental drift and involved forces, a Canadian geophysicist, J. Tuzo Wilson, proposed the theory of plate tectonics in 1965 by amalgamating seafloor spreading theory and the continental drift theory (Egger, 2003). According to Tuzo, the Earth’s crust or the lithosphere consists of large, hard pieces referred to as plates (van Hunen & van den Berg, 2007). The plates are floating on the beneath rock layer referred to as the asthenosphere. This sphere exposes rocks to intense pressure and heat to the extent that they are in the form of a viscous liquid. This theory showed that the idea of continental drift could have been flawed because the ocean crust and continental crust were components of plates, and they both drift over the Earth (Woods Hole Oceanographic Institution, 2005; Egger, 2003; Wilkins, 2011).
This theory claims that there are three types of boundaries between the plates, including the mid-ocean ridges (origin of the ocean crust), trenches (subduction zone), and the transform faults (where plates move) (Woods Hole Oceanographic Institution, 2005). Overall, the theory has offered an alternative, integrating explanation for major processes responsible for Earth’s features (Woods Hole Oceanographic Institution, 2005).
Current Evidence to Support the Plate Tectonics Theory
Scientists currently rely on powerful satellite technologies to gather evidence on plate tectonics. The GPS (global positioning system) and other satellite-supported data collection methods have allowed researchers to measure the Earth’s velocity (speed and direction of its surface), and they have determined that the movement of plates is estimated from 10 mm to 100 mm every year. This evidence shows that the Earth’s plates move, albeit, slowly but constantly.
The Himalayas were created about 40 million years ago because of the collision between the Indian Plate and the Eurasian Plate. The Indian Plate is now moving northwards, pushing the Himalayas upwards about 1 cm each year (Egger, 2003). Volcanoes, the mountain chains, and the advancing and receding seas are evidence of the plate tectonic theory founded on the continental drift theory.
Conclusion
The theory of the continental drift provided the modern knowledge of geology. Theorists, such as Wegener, Hess, and Tuzo, among others have advanced the understanding of the formation and mapping of the Earth. Hence, it is now acknowledged that the plate tectonics is the force responsible for the constant transformation of the Earth.
References
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