the Earth's interior

   

   Last week I have talked about the geologic time of the Earth. As we know, the Earth have been survived through a very very long time and will be live longer. we are just living in the shorter hundred years,so what can I do? don't mind, that 's just my qustion.
    Do you know how big the Earth? Do you know what it is  under our feets? Do you know how the Earth work? I didn't know before I have studied it, and I am amazed by the Earth. It's so wonderful!  let us look inside the Earth together.
    
     First, the way to learn about the earth's interior is to dig or drill a hole and examine it. however, this is only possible at shallow depths. The deepest the drill has ever penetrated is only 12.3kilometers, about 1/500 of the way to Earth's center! Even this was an extradinary accomplishment due to the rapid increases in temperature and pressure with path.
   


      Seismic waves are used to probe Earth's interior. The pattern of seismic waves are complacted beacause their behavior is influenced by different structures. Seismic waves travel fast through cold rock and slower through hot rock. Seismic waves reflect of layers composed different merterials. The results of seismic imaging of Earth's interior can be interpreted through comparsion with mineral physics experiments. These expriments recreat tempretaure and pressure within Earth, and allow scientists to see what rocks and metals are like at various depths.(date from the book of <Earth>)


   second, Earth is layered with the densest mertierals at the center and lighest mertierals forming the outer layer. This layer is a result of gravity,and is similar for all planets. Earth layers consist of the inner core(solid iron), outer core(liquid iron),mantle(dense rock),crust(low-denisty rock), ocean(water), and atmosphere(gas). Within layers,
   
You can look the movie of  The details about the inside of the earth that can make you to understande easily.




 In addition, Earth's tempreture increases from about 0℃ at the surface to through 5500℃ at the center. earth became very hot early in his history,scince then, Earth has slowly cooled.
   Moreover,Earth is not perfectly layered. three-dimensional structures within earth have been identfied by studying variations in Earth's graviational and magnetic fields and imaging called seismic tomography.
  As you see, I can't  relate everything about the interior of the Earth. It is so big and complex, and there are lots of regions that humans can't reach to. I know that some microbes can live inside the Earth, but I can't image it! the environment is too bad to live, how can they live there?
    we can stand on here, we can get water and air, we can live here, because of the big planet. The Earth give us eveything, the place where we are is the only one.

 

 

 

  

 

 

 

 

 

earth's evolution through geologic time

   In the late 18th centry, James Hutton recognized the immensity of  Earth history and the importance of time as a component in all geological processes. In the 19th centry, Sir Charles Lyell and others effectively demonstrated that Earth had experienced many episodes of mountain building and erosion, which must have required great spans of geologic time.
    Most geologic processes that shape the surface of the earth and give structure to its interior operate over long time, up to millions and billions of years. The igneous, metamorphic, and sedimentary rocks exposed at the surface are the visible record of the geological processes of the past. From the time and space relations that those rocks manifest, geologist have built the geologic time scale, which is used for placing the geologic event of earth history in sequence according to ralative age. Spontaneous decay of radioactive atoms in rocks gives absolute ages that date the geologic period and the origin of the earth.
    The only record we have of things that happened on Earth in the geological past is the rocks that were preserved from erosional destrution. If we were drill a hole into any spot on Earth we would find the rock the carry the geologic history of that spot. The depper the hole, the older the rocks would be and the longer the history they would disclose.
    

   Fossil, the ramain or trace of prehistoric life, are important in clusions in sediment and sedmentary life, are important tools for interpreting the geologic past. The scientific of fossil is called paleontology. It is an interdisciplinary science that blends geology and biology in an attempt to understand all aspects of the succession of life over the vast expanse of geologic time. Knowing the nature of life forms that existed at a particular times helps researchers understand past environmental conditions. Furture, fossil are important time indicators and play a key role in correlating rocks of similar ages that are from different places.

 Geologists have divided the whole geologic history into units of varying magnitude. Together, they comprise the geologic time scale of  Earth history. the major units of the time scale were delineated during the 19th century, principlly by workers in western europe ang Great Britain. Because radiometric dating was unavialable at that time, the entire time scale was created using  methods of relating dating. It was only in 20th centry that radiometric methods permited numerical dates to be added.


   The geologic time scale divided Earth's history into units of varying magnitude. It is commonly presented in chart form, with the oldest time and the event at the bottom and the youngest at the top. the principle subdivisions of the geologic time scale, called eons, inculde the Archean, Proterozoic(together, those two erons are commonly referred to as the precambrian), and ,begining about 524million years ago, the Phanerozoic(meaning "visible life")eron is divided into the following eras:Paleozoic("ancient life"), Mesozoic("middle life"), and Cenozoic("recent life").