Earth
Earth is the third planet from the Sun and the fifth largest. Its orbit is 149,600,000 km from the Sun, its diameter is 12,756.3 km, and its mass is 5.972e24 kg. Earth is the most dense planet there is in the solar system. The Earth is divided into several layers. They have distinct chemical and seismic properties.
One of them is the core. The core is probably made of mostly iron. It is also possible that some lighter elements are present, too. Temperatures at the center of the core is as high as 7500 K, which is hotter than the surface of the Sun. The lower mantle is made of mostly silicon, magnesium, oxygen, iron, calcium and aluminum. The upper mantle is made of mostly pyroxene, calcium, and aluminum.
Another is the crust. The crust varies considerably in thickness, it is thinner under the oceans, thicker under the continents. The inner core and crust are solid; the outer core and mantle layers are plastic or semi-fluid. The various layers are separated by discontinuities which are evident in seismic data; the best known of these is the discontinuity between the crust and upper mantle.
There are many plates under the Earth. The eight main plates are the North American Plate, the South American Plate, the Antarctic Plate, the Eurasian Plate, the African Plate, the Indian-Australian Plate, the Nazca Plate, and the Pacific Plate. There are also twenty or more small plates such as the Arabian, and Philippine Plates. Earthquakes are much more common at the plate boundary.