Eighth Grade Science Structure Review

Vocabulary flashcards for the eighth-grade science structure review, Third Semester, 2024-2025.

Seismic Waves

Vibrations inside and above the Earth's surface.

Focus

The location inside the earth where seismic waves originate and where rocks move.

Epicenter

The point on the Earth's surface directly above the focus of an earthquake.

Fault

A fracture or zone of fractures between two blocks of rock.

Primary Wave

A seismic wave that shakes the ground in the direction of the propagation, also known as a 'push-pull' wave. It travels through the Earth's interior.

Secondary Wave

A seismic wave that shakes the ground perpendicular to the direction of propagation. It travels through the Earth's interior but cannot pass through liquid.

Surface Wave

A seismic wave that travels along the Earth's surface, causing circular motion of the particles.

Seismologist

Scientists who study earthquakes.

Magma

Molten rock inside the Earth.

Lava

Molten rock that has erupted onto the Earth's surface.

Volcanic Ash

Tiny particles of shattered rock and volcanic glass ejected into the atmosphere during a volcanic eruption.

Silica

A chemical compound (SiO2) that affects the viscosity and density of molten lava.

Viscosity

A measure of a fluid's resistance to flow.

Composite Volcano

A volcano found in subduction zones and continental regions. It has a high silica content.

Shield Volcano

A volcano found at hotspots on both oceanic and continental crusts and along mid-ocean ridges. It has a low silica content.

Lahar

A mudflow composed of volcanic ash, debris, and water.

Pyroclastic Flow

A hot, fast-moving current of hot gas and volcanic matter that travels across the Earth's surface.

Fossil

The preserved remains or traces of an organism from the past.

Index Fossil

Fossils of organisms that lived for a relatively short period but were geographically widespread.

Law of Superposition

In undisturbed rock sequences, the oldest layers are at the bottom and the youngest are at the top.

Original Horizontality

The principle that layers of sediment are generally deposited in a horizontal or nearly horizontal position.

Lateral Continuity

The principle that rock layers extend continuously in all directions until they thin out or encounter a barrier.

Inclusions

Pieces of older rock that become part of a younger rock layer.

Cross-Cutting Relationships

The principle that a fault or intrusion is younger than the rock it cuts across.

Unconformity

A buried erosional surface separating two rock masses of different ages, indicating a gap in the geologic record.

Angular Unconformity

.An erosional surface on tilted or folded strata over which younger horizontal strata have been deposited.

Nonconformity

An unconformity in which stratified sedimentary rocks rest directly upon unstratified igneous or metamorphic rocks.

Disconformity

An unconformity between parallel layers of sedimentary rocks which represents a period of erosion or non-deposition.

Correlation

The process of matching rock layers or fossils from different locations to build a complete geologic record.

Isotopes

Different forms of the same element with the same number of protons but different numbers of neutrons.

Parent Isotope

The original, unstable radioactive isotope.

Daughter Isotope

The stable isotope formed from the radioactive decay of the parent isotope.

Radioactive Decay

The process by which an unstable atomic nucleus loses energy by emitting radiation.

Half-Life

The time it takes for half of the radioactive atoms in a sample to decay.

Absolute Age

The age of a rock or fossil in years, determined through radiometric dating methods.

Relative Age

The age of a rock or event compared to the ages of other rocks or events.

Paleozoic Era

An era that began with the Cambrian explosion of life in the oceans and ended with the largest mass extinction event in Earth's history.

Pangaea

A supercontinent that existed during the late Paleozoic and early Mesozoic eras.