The lively Earth: important features make the Earth unique
Name: Leung Ho Nam, Banson
The Earth is one of the eight planets in the solar system. The planet Earth is emphasized as “the rare Earth” in numerous literatures because of its unique physical conditions and the complicated interactions among all biotic and abiotic systems. Isotope dating indicates the earth was formed approximately from 4.53 to 4.568 Ga, according to isotope used (Allègre et. al., 1995). Despite the precise formation time of the Earth, there is no exact planet formation model that is generally accepted except the minimum mass solar nebula model, MMSN (Canup, 2008). The MMSN model suggested the planetary accretion of the Earth and other terrestrial planets begins with a disc of hydrogen abundant gas and dust, circulating around the sun. Following by a series of collision, small particles combine and collapse repeatedly. The runaway growth slows down until reaching a certain mass (Canup, 2008). The formation process is crucial to the evolution of the Earth because it determines the source of materials which the Earth contains.
The formation of the Earth, indeed, is not specific enough to comprise “the rare Earth” because all solar planets were grown within a circumsolar disc of gas and dust suggested by Canuo (2008). When we look at the solar system from the outer space, the Earth is probably the only shiny blue planet because of water surface reflection. 70 percent of the Earth surface is covered by the ocean. There is approximately 1.4 billion km2 of liquid water by mass on Earth (Oak & Kanae, 2006). The existence of permanent liquid water responsible to create a mild temperature and a stable environment. Liquid water is an important element implicates the emergence and evolution of life on Earth after a few million years from the latest collision (Baross & Hoffman, 1985).
The distinct blue colour of the ocean and the green colour of the terrestrial land is obvious on the Earth surface. Nevertheless, it is hardly to observe the entire view of the surface because of the scattering effect (Adams, 1934) and screening effect of the cohesive cloud in the atmosphere. Differences between the earth’s atmosphere and other planetary atmosphere including the presence of oxygen and relatively low carbon dioxide concentration. The atmosphere is extremely important to the biosphere. Without atmosphere, organisms nowadays would probably remain in the simple form or single celled. Furthermore, the ozone layer in the atmosphere absorbs and reflects part of the solar radiation incoming from the sun. This reduction of solar radiation lowers down the atmospheric temperature dramatically which allows organisms to survive.
The Earth would not be so unique among the solar system when missing either one of the systems. The Gaia hypothesis links this concept and indicates the Earth is a giant self-regulating system. The interactions of the organisms with their abiotic environments modified the condition of the Earth such as oxygen content and atmospheric temperature, making the Earth more habitable terrestrial planet (Lovelock, 1973).
Evolution of the Earth:
Allègre and the research team (1995) suggested that the Earth was formed 4.53 to about 4.7 Ga. The age range of the earth was estimated by means of a series of isotope dating so the results are relatively valid. The Earth queues the third planet from the sun and its average radius is 6371 km (Lide, 2000). Because of specific distance from the sun and the size, the Earth prevents some of the very light elements, such as hydrogen, from escaping, by gravitational force (Adams, 1934). Moreover, the Earth has a gravitational force of 10 g (Yoder, 1995). Gravitational force is an inconspicuous pull generated from the Earth core.
The Earth self-spins once it is formed. The rotation period of the earth is 23 hours and 56 minutes (Gold,...