Earth

EARTH

•    Earth is the third planet from the Sun and the only object in the Universe known to harbor life.
•    According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago.
•    Earth’s gravity interacts with other objects in space, especially the Sun and the Moon, Earth’s only natural satellite.
•    Earth revolves around the Sun in 365.26 days, a period known as an Earth year.
•    During this time, Earth rotates about its axis about 366.26 times.

LAYERS OF EARTH :
Crust
•    The solid crust is the outermost and thinnest layer of our planet.
•    The crust averages 25 miles (40 kilometers) in thickness and is divided in to fifteen major tectonic plates that are rigid in the center and have geologic activity at the boundaries, such as earthquakes and volcanism.
•    The most abundant elements in the Earth’s crust include (listed here by weight percent) oxygen, silicon, aluminum, iron, and calcium.
•    These elements combine to form the most abundant minerals in the Earth’s crust, members of the silicate family – plagioclase and alkali feldspars, quartz, pyroxenes, amphiboles, micas, and clay minerals.

Mantle
•    Mantle material is hot (932 to 1,652 degrees Fahrenheit, 500 to 900 degrees Celsius) and dense and moves as semi-solid rock.
•    The mantle is 1,802 miles (2,900 km) thick and is composed of silicate minerals that are similar to ones found in the crust, except with more magnesium and iron and less silicon and aluminum.
•    The base of the mantle, at the boundary with the outer core, is termed the Gutenberg discontinuity.
•    It is at this depth (1,802 miles, 2,900 km) where secondary earthquake waves, or S waves, disappear, as S waves cannot travel through liquid.
•    Scientists are utilizing seismic tomography to construct 3-dimensional images of the mantle, but there are still limitations with the technology to fully map the Earth’s interior.

Outer Core
•    The outer core is composed mostly of iron and nickel, with these metals found in liquid form.
•    The outer core reaches between 7,200 and 9,000 degrees Fahrenheit (4,000 and 5,000 degrees Celsius) and is estimated to be 1,430 miles (2,300 km) thick.
•    It is the movement of the liquid within the outer core that generates Earth’s magnetic field.

Inner Core
•    The inner core is the hottest part of our planet, at temperatures between 9,000 and 13,000 degrees Fahrenheit (5,000 and 7,000 degrees Celsius).
•    This solid layer is smaller than our Moon at 750 miles (1,200 km) thick and is composed mostly of iron.
•    The iron is under so much pressure from the overlying planet that it cannot melt and stays in a solid state.
•    The inner core is the hottest part of our planet, at temperatures between 9,000 and 13,000 degrees Fahrenheit (5,000 and 7,000 degrees Celsius).
•    This solid layer is smaller than our Moon at 750 miles (1,200 km) thick and is composed mostly of iron.
•    The iron is under so much pressure from the overlying planet that it cannot melt and stays in a solid state.

Lithosphere
•    The lithosphere is the outermost layer of the Earth 100 km thick and is defined by its mechanical properties.
•    This rigid layer includes the brittle upper portion of the mantle and the crust.
•    The lithosphere is divided into 15 major tectonic plates, and it is at the boundary of these plates where major tectonic occurs, such as earthquakes and volcanoes.
•    The lithosphere contains oceanic and continental crust that varies in age and thickness across locations and geologic time.
•    The lithosphere is the coolest layer of the Earth in terms of temperature, with the heat from the lower layers generating the plate movements.
•    The term “lithosphere” should not be confused with the use of “geosphere,” which is used to indicate all of Earth’s systems, including the atmosphere, hydrosphere, and biosphere.

Mesosphere
The mesosphere refers to the mantle in the region under the lithosphere and the asthenosphere, but above the outer core. The upper boundary is defined as the sharp increase in seismic wave velocities and density at a depth of 660 kilometers (410 mi). This layer should not be confused with the atmospheric mesosphere.