VOCABULARY Nº18

Superposition: the idea that in a series of rock layers the bottom layer is the oldest and the top is the youngest.








Relative age: the age of a rock compared with another rock.





Geologic column: a listing of Earth's rock layers in order from oldest to youngest.








Fossil: any trace, imprint, or remains of a living thing preserved in Earth's crust.








Index fossil: the remains of a living thing that was widespread but lived for only a short part of Earth's history.








Half-life: the time it takes for half the mass of an original element to change into a new product.





Absolute age: the age of a rock in year.





Era: one of the long stretches of time that Earth's history is divided into.

VOCABULARY Nº17

Mineral: a naturally occurring solid in earth's crust with a definite structure and composition.








Igneous rock: a rock that forms when hot, liquid rock material cools and hardens into a solid.








Sedimentary rock: a rock that forms from pieces of other rocks that are squeezed or cemented together.








Metamorphic rock: a rock that forms from another kind of rock that is changed by heat or pressure or by a chemical reaction.








Rock cycle: rocks continually changing from one kind into another in a never-ending process.

VOCABULARY Nº16

Mass wasting: the downhill movement of Earth material caused by gravity.








Deposition: the dropping off of sediment.








Glacier: a huge sheet of ice and snow that moves slowly over the land.








Till: a jumble of many size of sediment deposited by a glacier.








Moraine: a deposit of many size of sediment in front of or along the sides of a glacier.

VOCABULARY Nº15

Fold mountain: a moountain made mostly of rock layers.








Fault-block mountain: a mountain made by huge titled.





Weathering: the breaking down of rock.





Erosion: the picking up.





Soil: a mixture of weathered rock.





Soil horizont: any of the layers of soil.





Groundwater: water that soaks into soil and rock.





Humus: material in soil.

VOCABULARY Nº14

Hot spot: a very hot part of the mantle, where magma can melt through a plate moving above it.





Vent: a central opening in a volcanic area through which magma may escape.









Lava: magma that reaches Earth's surface and flows out of a vent.







Crater: a cuplike hollow that forms at the top of a volcano around the vent.








Cinder-cone volcano: a steep-sided cone that forms from explosive eruptions of hot rocks, ranging from particles to boulders.








Shield volcano: a wide, gently sloped cone that form from flows of lava.








Composite volcano: a cone formed from explosive eruptions of hot rocks followed by a flow of lava, over and over.








Geothermal energy: heat from below Earth's surface.