the Earth's systems

    Earth is warmed by the absorption of visible radiation from the Sun and is cooled by the emission of infrared radiation to space. Much of the infrared radiation by Earth's surface is absorbed and reemitted by atmosphere gases. The result is a greenhouse effect that warms the surface by about 33℃. Without this natural greenhouse effect, Earth would be too cold to support life.
   The driving force for the atmospheric circulation is the global distribution of energy. The angle at which the Sun's ray strike Earth changes from the equator toward the poles, The result is that incoming solar radiation decreases with latitude. More solar radiation is received in the tropics than at the poles, resulting in an equator-pole temperature gradient. The temperature gradient drives the atomosperic circulation because of the inverse relationship between the temperature and the density of a gas: higher temperature produce lower densities. Differences in the distribution of global temperature cause differences in air density and, therefore pressure. Air tend to move from areas of high pressure to areas of low pressure. These large-scal movement of air produce the global wind belts.
    As with the atmosphere, the driving force for the oceanic circulation is the global distribution of energy. Unlike the atmosphere, however, the ocean circulation is driven by indirectly by temperature differences: the surface-ocean circulation is, in fact, driven by the circulation of atmosphere. Due to friction, wind blowing over the ocean surface water along, producing ocean currents. The pattern of surface-ocean currents is modified by the Coriolis effect, a consequence of Earth's rotation, and by the distribution of land and oceans,
   The solid Earth is dynamic, not static. Wegener's idea of drifting continent proposed in the early 20th century has largely been substantiated. New seafloor is created at mid-ocean ridges and moves outward as oceans basins grow. Old seafloor is distorted  at deep-sea trenches in subduction zones. Earthquake outline the surface of the slab of oceanic lithosphere being sub-ducted beneath the continent; their foci along a continental margin become ever deeper away from the trench. Deeper probing of Earth's interior has revealed heterogeneity in composition and temperature that can be the result only of large-scale circulation in the mantle or the outer core.
  There is also the global carbon cycle that occur on land and in oceans and involve both biological and nonbiological chemical reaction on the Earth.
   Some of the characteristics of life that allow it to play an important role in the Earth system are its tendency toward exponential growth, its need for energy, its tendency to pollute, and tis versatility.
   The circulations of the atmosphere, oceans, solid and energy and so on are support the Earth and the life. They are play an important role on the working of the earth.

the early evolution of life

    Hello,  I had a little trouble about my work, and I believe that I can do it well.  How about you?  Do you have troubles? You can tell me. haha  
    Earth is the only planet on which we have confirmed the existence of life, past or present. life originated on Earth as much as 3.9 billion years ago. Three steps must have been accomplished on the way to the complex life forms we know today: (1) chemosynthesis of small organic molecules from inorganic precursors; (2) biosynthesis, the polymerization of small organic molecules to form biopolymers, especially protein; and (3) the development of the complex chemical machinery needed for metabolism and replication. The specific mechanism by which life originated are still hypothetical.
   Life contribute to the chemical evolution of the Earth system through the buildup of oxygen and sequestration of carbon. Oxygenation happened over a long time, but the onset of major oxygenation coincides roughly with the beginning of the Proterozoic Eon. Once the ozone layer began to absorb harmful shortwave radiation, organisms would have been able to survive in shallow waters; this critical stages was reached around 600 million years ago, just before the onset of Phanerozoic Eon. The emerging biosphere had had a profound impact on carbon cycling; limestone and organic sediment provide long-term storage reservoirs for carbon, sequestering it form the atmosphere and hydrosphere.
   The most ancient known fossil are 3.55 billion years old, found in rocks from Archean Eon. Some early fossils are the remains of microscopic procaryotes; others are stromatolites that precipitated as a result of bacteria influencing the chemistry of seawater. The dominated Earth for about 2 billion years, was prokaryotic and anaerobic. Anaerobic cells acquire energy by fermentation, which restricts them to a small size and limits their structural complexity. The first photosynthetic prokaryotes were probably cyanobacteria.
    The first land plants were seedless; these evolved into naked-seed plants, and grasses. Arthropods were probably the first animal to move from sea to land. Pikaia, the first known chordate, was jawless; jawed fish evolved later. The first to venture onto land were crossopterygians, which give rise to amphibians. Amphibians have permeable skins and lack a moist environment for reproduction, and thus  remain dependent on the aquatic environment. Reptiles became liberated form the water by evolving a water-tight skin and an egg with a shell; they evolved into two orders of dinosaurs and two new verterbrate classes__mammals and birds.
    The first clearly bipedal hominid was Australopithecus, whose fossils range from about 3.9 to 3.0 million years in age. Fossil of Homo erectus, possibly the first spices of our own genus, dates to about 1.8 million years ago. Homo erectus disappeared 300,000 years ago and was replaced by Homo neanderthalensis, The poor fossil record between 400,000 and 100,000 years ago has made it difficult for scientists to determine how the transition occurred, but DNA studies suggest that Homo sapiens is not a direct descendant of Neanderthals. The Neanderthals disappeared about 30,000 years ago and were replaced by the first indisputable members of our own species, Homo sapiens.
    About 99 percent of the species that have lived on Earth are now extinct. Extinction is a natural process, but it has not happened at a constant rate over geologic time. Superimposed on background extinctions are at least five major mass extinction events, in which many types of organisms died out over short periods. These may have been caused by climatic and other environmental changes, possibly accelerated by major meteorite impacts, massive episodes of volcanism, or the formation of supercontinents. Humans have greatly accelerated the rate of extinction of species.






    

Natural and environmental hazard

    Hello, how about your work today? how about your study today?
    I'm fine,but a small earthquake was happened yesterday. I think some natural hazards like earthquake are occur on the earth anytime. Today I will talk about the geologic hazards on the earth.  
   A geologic hazard is a natural geologic event that can endanger human lives and threaten human property. Earthquakes, geomagnetic storms, landslides, sinkholes, tsunamis, and volcanoes are all types of geologic hazards.
   Earthquakes occur all over the world and often occur without significant warning. These geohazards can have far-reaching affects on humans and on the surface of the Earth. Small, localized earthquakes may cause no noticeable damage and may not even be felt by people living in the affected area. In contrast, a large earthquake may cause destruction over a wide area and be felt thousands of miles away.Earthquakes can also occur within plates, although plate-boundary earthquakes are much more common. Less than 10 percent of all earthquakes occur within plate interiors. As plates continue to move and plate boundaries change over geologic time, weakened boundary regions become part of the interiors of the plates. These zones of weakness within the continents can cause earthquakes in response to stresses that originate at the edges of the plate or in the deeper crust. The New Madrid earthquakes of 1811-1812 and the 1886 Charleston earthquake occurred within the North American plate.While we can't prevent earthquakes or even accurately predict when they will occur,but what we should to know is how to be prepared for an earthquake and what to do if one occurs.
    A landslide is the movement of soil, rock, or other earth materials, downhill in response to gravity. Landslides include rock falls and topples, debris flows and debris avalanches, earthflows, mudflows, creep, and lateral spread of rock or soil. Landslides constitute a major geologic hazard, they are widespread, occurring in all 50 States, and they cause more than $2 billion in damages and more than 25 fatalities on average each year.One of the largest landslides in the world is in the 20th century occurred at Mount St. Helens, Washington, in 1980. A moderate earthquake caused roughly 1.7 cubic miles of rocks and mud to break free and slide down the side of the volcano, releasing pent-up pressure to produce the major eruption of May 18.
  A volcano is a vent at the Earth's surface through which magma and associated gases erupt, and also the cone built by eruptions. A volcano that is currently erupting or showing signs of unrest (earthquakes, gas emissions) is considered active. A volcano that is not currently active but which could become active again is considered dormant. Extinct volcanoes are those considered unlikely to erupt again. Volcanic eruptions are one of Earth's most dramatic and violent agents of change. They pose significant geologic hazards because their eruptions and associated activities can affect large areas and go on for extended periods of time. Many kinds of volcanic activity can endanger the lives of people and property, and the affects of these activities are felt both close to and far away from the volcano. Explosive eruptions can spread lava, gas and other materials over a wide area, and may drastically alter the landscape. Slow eruptions or flows can also alter landscapes, while associated earthquakes, atmospheric effects, landslides, and floods all may damage or destroy property and threaten human lives.
   Tsunamis are large, destructive waves that are caused by the sudden movement of a large area of the sea floor. Most tsunamis are caused by earthquakes, some are caused by submarine landslides, a few are caused by submarine volcanic eruptions and on rare occasions they are caused by a large meteorite impact in the ocean.The Krakatau volcanic eruption of 1883 generated giant waves reaching heights of 125 feet above sea level, killing thousands of people and wiping out numerous coastal villages. Locally generated tsunamis may reach a shoreline with only a few minutes warning, while distant events may allow several hours warning. In addition, many coastal areas have tsunami alert systems that sound sirens or provide information through local media. While we can't prevent tsunamis, we can take steps to lessen their impact. Those who live in or visit tsunami-prone areas should know the warning signs of an approaching tsunami, and what to do when a tsunami is imminent.
  We live on the earth which has too many natural and environmental hazards, and here I just have talked some. Also, hazards like flood, Glossary of Terms and Sinkholes can't be looked down upon.
   We can't change the natural hazard, but we can change the man-made hazard what we do on the earth. Before we protect our lives, we should protect the Earth. If we save the food and water, if we protect the rare species of animals, plants and other living things, the earth will be better, we will be live longer.