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The Secret of Earth's Double Crust: Why Are Oceanic and Continental Crusts So Different?
Earth's crustal evolution covers the formation, destruction, and regeneration of the rocky outer shell on the planet's surface. Compared to other Earth-like planets such as Mars, Venus, and Mercury, Earth's crust has greater variation in composition. This unique property reflects a complex set of crustal processes that have occurred throughout the planet's history, including ongoing plate tectonics. The early development of the Earth's crust, the dichotomy of the crust and the formation of its different types of crust are all fundamental reasons for shaping the Earth into what it is today.
The formation mechanism of the early crust
Earth was completely molten in its early stages, due primarily to high temperatures generated by several processes: compression of the early atmosphere, rapid rotation, and frequent collisions with nearby asteroids. As the planet cools, the heat stored in the lava ocean is gradually lost through radiation as the planet's coalescence slows. The theory that posits the beginning of lava solidification states that once it is cold enough, the cooling of the bottom of the lava ocean will first begin crystallization.
During this period, a thin "cooling crust" may have formed on the Earth's surface, providing thermal insulation for the molten rock below, maintaining temperatures high enough for continued crystallization of the deep molten rock.
Crustal dichotomy
The crustal dichotomy refers to the sharp contrast in composition and properties between the oceanic crust and the continental crust. Currently, both oceanic and continental crust are continuously generated and maintained through the process of plate tectonic plates. However, these mechanisms are unlikely to have led to the formation of early crustal dichotomy, based on the observation that different densities enabled subduction of the plates.
Formation process
In the early Earth, the formation of impact craters had an important influence on the evolution of the crust. Impact craters are found all over the solar system, caused by frequent meteorite strikes during a period known as the Late Heavy Bombardment. The Earth's high erosion rate and ongoing plate movement make these traces almost indiscernible.
According to speculation, at least 50% of the Earth's original crust was covered by various impact craters, indicating that impact cemeteries have a profound impact on the Earth's surface.
Types of Earth's Crust
The crust can be mainly divided into three categories: primary crust, secondary crust and tertiary crust. The primary crust was formed by crystallization from the molten magma ocean about 4.4 billion years ago. The secondary crust was formed by partial melting of the primary crust material. The current continental crust belongs to the tertiary crust, which is far more Unlike the rest of the Earth. This diversity is due to the recycling and filmic processes of the Earth's crust.
The Beginning of Plate Tectonics
The beginning of plate tectonics can be traced to the formation of thermal plumes. The rise of this heat column affects the movement of the earth's crust. With the existence of the heat column, parts of the earth's crust are forced to sink and then begin to subduct. In addition, the effects of the Late Heavy Bombardment may have also intensified convection in the mantle, leading to the separation of the crust.
Reflections of the contemporary crust
Some geological features in modern Iceland are thought to be very similar to features of earlier Earth's crust. The high iron content and specific chemical composition of these zones provide valuable clues to our understanding of the formation and evolution of the early Earth's crust.
The evolution of the earth makes us think about what new changes it will have in the future?
