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 Michelle Mindick The Evolution of Earth’s Surface According to 21st Century Astronomy, Earth originally formed as a result of gas and dust that rotated around a protostar -­‐ our sun-­‐ billions of years ago. This process eventually lead to clumps of rock, metal, ice and other organic materials which formed a particular distance away from what we now know as the sun, giving us the planet Earth upon which we were fortunately able to have risen into existence. The Earth is an ever evolving planet and does not remain idle although these changes seem to go undetected by our senses. There are many factors that go into the sculpting of the Earth’s surface; some of these natural influences include tectonism, volcanism, gradation, impact cratering, and Earth’s interior core. In order to understand a significant aspect of Earth’s surface, one must look deep into the Earth’s inner core where its original thermal energy is contained. Much of this thermal energy was derived from the energy present during an array of collisions that took place. This series of impacts, along with radioactive materials, melted the planet and led to the formation of the planet and billions of years ago. After this short-­‐lived melting, the planet cooled down rapidly through a process where energy was released into space, which laid the foundations for the crust to form on the outer layer of the Earth’s surface. The inner core alone is not enough to explain the heating of the Earth, and so we look somewhat to tidal effects from the moon and sun which provide friction and therefore heat. The other factor in the heating of Earth is long lasting radioactive elements which are trapped deep in the interior of the Earth, which when they decay further generate heat. As this happens simultaneously, the Earth continues to release heat into space and consequently progresses to cool off. 1 A second component which greatly influences the topography of Earth is crater impacts. When the Earth was originally formed, debris orbited around in the solar system and crashed into each other, sometimes in such a way that caused the formation of larger objects, but often these collisions were destructive. These collisions are still evident today and have been known to break through earth’s atmosphere, causing great craters on the earth’s exterior. A multitude of changes happen as these collisions occur. According to 21st Century Astronomy, when an object crashes into a planet, its energy is put forth towards heating and compressing the surface with which it has come in contact. Not only does it affect the area that it hits directly, but the impact also causes excess material to be launched far away from the outer boundaries of the initial collision, which often cause “secondary craters.” An additional result of these collisions is a peak which rises at the center of the crater floor called the “underlying strata rebound.” A few more things happen to the surface of the Earth where a crater is formed. First, the energy of the impact often causes the vaporization of rock and soil which creates cooled pools of melted rock on the surface. Second, new minerals form as this high-­‐energy process occurs. One notable change that occurred as a result of a meteor collision to the Earth is the extinction of over 70% of all living species inhabiting the Earth about 65 million years ago. Evidence of this life-­‐altering period on our planet is marked by large amounts of iridium found in the layer of bedrock which corresponds to this period during Earth’s existence. This iridium is believed to be deposited by the meteor as we know that this element is prevalent in meteors, and equally significantly it is absent around the rest of the Earth. 2 Earth’s surface has continued to shift over time, and this shift is a major reason for the greatly altered terrain of our planet. One cause of this shift is gravity’s pull on the accumulation of solidified rock and sediment that has been transferred by the movement of rivers. This gravitational pull causes rock layers to bend and break along fault lines. A second reason for the deformation of Earth’s surface is the continental drift, which is the widely accepted theory of Alfred Wegener. This idea originated when he observed that the continents seemed to be parts that would fit together to make a whole. It is the theory that the continents were once one large land mass and have since drifted astray into the various continents we now know. A third and extremely crucial factor for the shift of the Earth is caused by the planet’s “outer shell,” which is made of up of numerous plate tectonics. These plate tectonics are forced to shift by the convection, or heating, of radioactive decay which causes thermal energy at the mantel of the Earth. As material rises and spreads out at a certain location (convection), it will undoubtedly collide and converge in another area, leading to the carrying of continents as well as ocean crust. This process leads to earthquakes, which are the result of plates pushed together with such force that the stress is released as the plates slip past each other. Volcanism is a second result of the friction that occurs between plates that causes rock to melt and be pushed up through the surface. The molten lava that erupts from these volcanoes flows about the surface and hardens, destroying and engulfing anything it reaches – another reason for the evolving landscape of the Earth. Finally, a common aftermath of plate tectonism, as plates buckle and break, is that they form large mountain ranges. 3 The final, significant contributor to Earth’s ever-­‐changing topography is the result of various processes of gradation. As earthquakes, volcanoes, and impact craters break up and reform Earth’s surface, gradation levels it through chemical and physical weathering. Rocks along shorelines, for example, are constantly broken up by the impact of waves and other bits of rocks. Chemical reactions also occur in order to destruct certain materials, such as when oxygen and iron form rust on rocks. Freeze-­‐thaw cycles occur when water runs into cracks where it then freezes and expands, causing the rock formations around it to fracture. After these various processes weather down the bedrock, bits of rock fragments can easily be washed away by moving water, wind, or glacial ice and delivered to other areas as sediment. This process causes formations such as sand dunes, river deltas, and mounds of sediment at the bottom of mountains and cliffs. Gradation is such a powerful progression of events that it even has the capacity to weather down and fill in impact craters. Our Earth has been through an extremely turbulent life span, an ever-­‐evolving circumstance of creation and destruction. There are a series of various processes that contribute greatly to the formation and deformation of the planet’s fragile surface. The Earth’s inner core emits thermal energy that affects its ability to sustain life as well as contributes to the heating of volcanic magma which is erupted to the surface by the strain of tectonic plates, causing the terrain to shift and rearrange. Impact craters force massive depressions in the Earth’s surface while simultaneously melting the rock and soil, leading to the formation of new minerals in that region. The continental drift, earthquakes, and formation of volcanoes are the planet’s natural reaction to convection occurring in the center of the Earth’s mantle. Finally, gradation chemically erodes materials and transfers rock debris to other locations by way 4 of flowing water and wind. All of these natural processes occur due to the reactions of one another and cause the earth to continuously move forth in its wonderfully active, ever transforming existence. References Greeley, R., (2007). 21st Century Astronomy: The Solar System New York, NY & London. W.W. Norton & Company 5