What is the earths crust mostly made of

aluminum     A metallic element, the third most abundant in Earth’s crust. It is light and soft, and used in many items from bicycles to spacecraft.

behavior     The way something, often a person or other organism, acts towards others, or conducts itself.

continent     (in geology) The huge land masses that sit upon tectonic plates. In modern times, there are six established geologic continents: North America, South America, Eurasia, Africa, Australia and Antarctica. In 2017, scientists also made the case for yet another: Zealandia.

convection     The rising and falling of material in a fluid or gas due to uneven temperatures. This process occurs in the outer layers of some stars.

core     Something — usually round-shaped — in the center of an object. (in geology) Earth’s innermost layer. Or, a long, tube-like sample drilled down into ice, soil or rock. Cores allow scientists to examine layers of sediment, dissolved chemicals, rock and fossils to see how the environment at one location changed through hundreds to thousands of years or more.

crust     (in geology) Earth’s outermost surface, usually made from dense, solid rock.

crystal     (adj. crystalline) A solid consisting of a symmetrical, ordered, three-dimensional arrangement of atoms or molecules. It’s the organized structure taken by most minerals. Apatite, for example, forms six-sided crystals. The mineral crystals that make up rock are usually too small to be seen with the unaided eye.

current     A fluid — such as of water or air — that moves in a recognizable direction. (in electricity) The flow of electricity or the amount of charge moving through some material over a particular period of time.

decay     (for radioactive materials) The process whereby a radioactive isotope — which means a physically unstable form of some element — sheds energy and subatomic particles. In time, this shedding will transform the unstable element into a slightly different but stable element. For instance, uranium-238 (which is a radioactive, or unstable, isotope) decays to radium-222 (also a radioactive isotope), which decays to radon-222 (also radioactive), which decays to polonium-210 (also radioactive), which decays to lead-206 — which is stable. No further decay occurs. The rates of decay from one isotope to another can range from timeframes of less than a second to billions of years.

density     The measure of how condensed some object is, found by dividing its mass by its volume.

diamond     One of the hardest known substances and rarest gems on Earth. Diamonds form deep within the planet when carbon is compressed under incredibly strong pressure.

earthquake     A sudden and sometimes violent shaking of the ground, sometimes causing great destruction, as a result of movements within Earth’s crust or of volcanic action.

Earth’s crust     The outermost layer of Earth. It is relatively cold and brittle.

element     A building block of some larger structure. (in chemistry) Each of more than one hundred substances for which the smallest unit of each is a single atom. Examples include hydrogen, oxygen, carbon, lithium and uranium.

field     An area of study, as in: Her field of research was biology. Also a term to describe a real-world environment in which some research is conducted, such as at sea, in a forest, on a mountaintop or on a city street. It is the opposite of an artificial setting, such as a research laboratory. (in physics) A region in space where certain physical effects operate, such as magnetism (created by a magnetic field), gravity (by a gravitational field), mass (by a Higgs field) or electricity (by an electrical field).

iron     A metallic element that is common within minerals in Earth’s crust and in its hot core. This metal also is found in cosmic dust and in many meteorites.

Isaac Newton     This English physicist and mathematician became most famous for describing his law of gravity. Born in 1642, he developed into a scientist with wide-ranging interests. Among some of his discoveries: that white light is made from a combination of all the colors in the rainbow, which can be split apart again using a prism; the mathematics that describe the orbital motions of things around a center of force; that the speed of sound waves can be calculated from the density of air; early elements of the mathematics now known as calculus; and an explanation for why things “fall:” the gravitational pull of one object towards another, which would be proportional to the mass of each. Newton died in 1727.

lithosphere     The upper layer of Earth, which includes its thin brittle crust and upper mantle. The lithosphere is relatively rigid and is broken into slowly moving tectonic plates.

magnesium     A metallic element that is number 12 on the periodic table. It burns with a white light and is the eighth most abundant element in Earth’s crust.

magnetic field     An area of influence created by certain materials, called magnets, or by the movement of electric charges.

mantle     (in geology) The thick layer of the Earth beneath its outer crust. The mantle is semi-solid and generally divided into an upper and lower mantle.

metal     Something that conducts electricity well, tends to be shiny (reflective) and malleable (meaning it can be reshaped with heat and not too much force or pressure). 

moon     The natural satellite of any planet.

nickel     Number 28 on the periodic table of elements, this hard, silvery element resists oxidation and corrosion. That makes it a good coating for many other elements or for use in multi-metal alloys.

oxygen     A gas that makes up about 21 percent of Earth's atmosphere. All animals and many microorganisms need oxygen to fuel their growth (and metabolism).

pressure     Force applied uniformly over a surface, measured as force per unit of area.

radioactive decay     A process by which an element is converted into a lighter element through the shedding of subatomic particles (and energy).

radius     A straight line from the center to the circumference of a circle or sphere.

range     The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists.

semi     An adjective meaning “somewhat.”

shell     The protective, hard outer covering of mollusk or crustacean, such as a mussel or crab.

silica     A mineral, also known as silicon dioxide, containing silicon and oxygen atoms. It is a basic building block of much of the rocky material on Earth and of some construction materials, including glass.

silicon     A nonmetal, semiconducting element used in making electronic circuits. Pure silicon exists in a shiny, dark-gray crystalline form and as a shapeless powder.

slide     In microscopy, the piece of glass onto which something will be attached for viewing under the device’s magnifying lens.

solid     Firm and stable in shape; not liquid or gaseous.

sun     The star at the center of Earth’s solar system. It’s an average size star about 26,000 light-years from the center of the Milky Way galaxy. Also a term for any sunlike star.

tectonic plates     The gigantic slabs — some spanning thousands of kilometers (or miles) across — that make up Earth’s outer layer.

thorium     A naturally radioactive element which appears as a silvery metal when it is pure. It reacts chemically with air, turning black on its surface. It is found in some minerals, and can be used to trace the source of some mineral grains that are carried long distances by water or wind. Its scientific symbol is Th.

turbulent     (n. turbulence)  An adjective for the unpredictable fluctuation of a fluid (including air) in which its velocity varies irregularly instead of maintaining a steady or calm flow.

uranium     The heaviest naturally occurring element known. It’s called element 92, which refers to the number of protons in its nucleus. Uranium atoms are radioactive, which means they decay into different atomic nuclei.

wave     A disturbance or variation that travels through space and matter in a regular, oscillating fashion.