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Questions and Answers
Which type of seismic wave is also known as a compressional wave?
During which geologic era do we currently live?
Which feature represents the edge of the continental crust?
What is the primary cause of earthquakes?
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What do we call the point on the Earth's surface that is directly above the focus of an earthquake?
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What percentage of the Earth's surface is occupied by oceans?
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What are mountain roots?
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What is the primary concept explained by the elastic rebound theory?
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What is formed when divergent boundaries occur?
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Which process transforms existing rocks into metamorphic rocks?
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What type of rock is characterized by high silica content?
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What occurs at convergent boundaries?
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Which is NOT a feature associated with convergent boundaries?
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How many major lithospheric plates does the Earth's lithosphere have?
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What is the main component of rocks?
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Who proposed the theory of continental drift?
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Which feature differentiates oceanic crust from continental crust?
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What type of rock is formed from the solidification of molten magma or lava?
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What is the primary composition of the outer core of the Earth?
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How does the lithosphere move in relation to the asthenosphere?
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What characteristic allows the asthenosphere to facilitate tectonic plate movement?
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What occurs at the boundaries of tectonic plates?
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Which type of igneous rock forms from magma that crystallizes slowly beneath the Earth's surface?
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What is the role of the inner core in relation to the Earth's structure?
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Study Notes
Earth’s Surface Composition
- 29% of Earth’s surface is land and 71% is ocean.
- Continental shelf area increases the land area to 35% and decreases the ocean basin area to 65%.
Oceanic Relief Features
- Mid-oceanic ridge with a central rift where crust is pulled apart.
- Continental shelves accumulate thick deposits of continental sediments.
- Continental slopes are the edge of the continental crust.
- Oceanic trenches are where oceanic crust slides beneath continental crust.
Continents
- Divided into active mountain-making belts and inactive regions of old, stable rock.
- Continental shields and mountain roots are two types of stable structures.
- Mountain Roots are the deep, stable portions of the Earth's crust that support mountain ranges.
Time Scale
- Time older than 570 million years (MY) is Precambrian time.
- Three eras of time follow: Paleozoic, Mesozoic, and Cenozoic.
- Geologic eras are subdivided into periods.
- We live in the Holocene period (the last 12,000 years).
Earthquakes
- Shaking and trembling caused by rock movement beneath Earth's surface.
- Most severe earthquakes occur near plate collision boundaries.
- Earthquakes are the sudden release of stored energy.
- Result of fast movement between two blocks of rock.
- Released energy radiates away from the earthquake.
- Main cause of earthquakes is faults on the Earth's crust.
- A fault is a break between two blocks of rocks.
Earthquake Terminology
- The origin of the earthquake (where the fault begins) is the focus or hypocenter.
- The point on the Earth's surface directly above the focus is the epicenter.
Elastic Rebound Theory
- Explains how energy is stored in deformed rocks along fault lines and released during an earthquake.
- Seismic waves are vibrations that travel through Earth carrying energy released during an earthquake.
Seismic Waves
- Two types of waves produced during an earthquake.
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Body waves: travel through Earth’s interior.
- P wave (primary): compressional wave that causes alternate compression and expansion of the rock.
- Surface waves: travel along the Earth’s surface.
Metamorphic Rocks
- Created when existing rocks are transformed by heat, pressure, or chemically active fluids.
- This process, known as metamorphism, changes the mineral composition and structure.
Earth's Composition
- 91 elements occur naturally in the Earth’s crust.
- Eight elements make up more than 98 percent of the earth’s crust.
- A mineral is a naturally occurring, inorganic solid with a characteristic chemical composition and a crystalline structure.
- Felsic rocks (comprising the crust) are high in silica content.
- **Ultramafic rocks **(comprising the mantle) are high in magnesium and iron content.
Plate Tectonics
- The theory proposed by Alfred Wegner in 1912 suggests that the crustal plates are moving over the mantle.
- Wegner proposed that today’s continents once formed a single landmass, called Pangaea.
- The uppermost mantle and the overlying crust behave as a strong, rigid layer, known as the lithosphere, which is broken into segments called plates.
Lithospheric Plates
- The Earth’s lithospheric shell is divided into six great lithospheric plates and at least nine lesser plates.
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Divergent boundaries (Constructive): two plates slide apart from each other. They are characterized by:
- Rift valleys
- Tilted block mountains
-
Convergent boundaries (Destructive): two plates slide towards each other, forming either a subduction zone or a continental collision. They are characterized by:
- Trenches
- Mountain ranges
- Island arcs
- Volcanic arcs
- Transform boundaries (Conservative): plates slide past each other along transform faults.
Earth Structure and Composition
- The layers of the Earth’s interior include the crust, mantle, liquid outer core, and solid inner core.
- Crust: outermost layer, thinnest and solid, composed of continental and oceanic crust.
- Mantle: thick layer beneath the crust, semi-solid rock that flows slowly.
- Outer Core: Liquid layer beneath the mantle, composed mainly of iron and nickel.
- Inner Core: innermost layer, solid sphere due to high pressure, primarily iron and nickel.
Lithosphere and Asthenosphere
- Lithosphere: rigid outer layer of Earth (crust + upper mantle).
- Asthenosphere: semi-fluid layer of the upper mantle beneath the lithosphere.
Rocks
- Rocks are aggregates of mineral particles.
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Igneous Rocks: formed from the solidification of molten magma or lava.
- Intrusive (Plutonic): crystallize slowly beneath the Earth's surface.
- Extrusive (Volcanic): erupt and cool quickly on the surface.
- Sedimentary Rocks: formed from the accumulation and compaction of sediments.
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Description
Explore the composition of Earth's surface and the various geological features found within our oceans and continents. This quiz covers land-to-ocean ratios, oceanic relief features, and the geological timescale, including major eras and periods. Test your knowledge about the Earth's structure and its history!
