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Grade 7 / Middle 1 (age 12-13)

Tectonic Activity

Tectonic Activity

Earth's interior has crust, mantle, outer core, and inner core. Mantle convection drives the plates, and convergent, divergent, and transform boundaries build mountains, ridges, and quakes. Most earthquakes and volcanoes sit at plate edges, and P and S waves reveal the interior. Press the buttons to switch among the three boundary types and explore the landforms.

What is Earth's Interior Like?
💡 Earth's Structure
①Crust: thin outer shell (5–70 km)
②Mantle: thickest layer, convection motion
③Outer core: liquid iron + nickel
④Inner core: solid under enormous pressure
Plates Move — Types of Boundaries
🌍 Plate Boundaries & Tectonics
①Convergent: collision → mountains, trenches, volcanoes
②Divergent: separation → ridges, rifts, new crust
③Transform: sliding → earthquakes (San Andreas Fault)
④Mantle convection drives plate motion
Earthquakes & Volcanoes

Earthquakes vs Volcanoes

ChartEarthquake vs Volcano Comparison
AspectEarthquakeVolcano
CausePlate collision/slidingMagma eruption
LocationPlate boundary (fault)Convergent/divergent boundary
ResultGround shakingLava and ash eruption
MeasurementRichter magnitudeVolcanic Explosivity Index (VEI)
Types of Seismic Waves
P-wave (primary, fast) → S-wave (shear, slower) → surface wave (most damage)
P-waves arrive first; surface waves cause the worst damage
🌋 Earthquakes and Volcanoes
①Most occur at plate boundaries
②Pacific Ring of Fire: concentrated quakes/volcanoes
③Seismic waves reveal Earth's interior
④P-waves pass through solid + liquid; S-waves only solid
Exam Key Points
Core Summary
Mantle convection → plate motion → quakes, volcanoes, mountains
Surface changes stem from internal energy (mantle convection)
🎯 Exam Key Points
①Interior layers: crust-mantle-outer core-inner core
②Driver of plate motion: mantle convection
③Convergent: mountains/trench / Divergent: ridge/rift / Transform: earthquake
④Speed: P > S > surface waves
⑤Pacific Ring of Fire: most active
Examples and Unit Test
Example 1
List the inside of the Earth from the outside inward, and which layer is in a liquid state?
1
From the outside in, the inside of the Earth is crust → mantle → outer core → inner core.
2
The outer core is liquid (iron and nickel), while the inner core is solid under high pressure.
Crust → mantle → outer core → inner core / liquid = outer core
The inside of the Earth is crust, mantle, outer core, and inner core; only the outer core is liquid.
Example 2
What landforms are made at a boundary where two plates collide, and what is this boundary called?
1
A boundary where plates collide is called a convergent boundary.
2
At a convergent boundary the two plates collide to form mountains or trenches, and earthquakes and volcanoes occur.
Mountains and trenches form / a convergent boundary
Convergent boundaries collide (mountains/trenches), divergent ones separate (ridges), and transform ones slide past (earthquakes).
Unit-test style
Which statement about tectonic activity is correct?
The thickest layer of the Earth is the crust
Mantle convection is the driving force that moves the plates
The outer core is in a solid state
At a divergent boundary, two plates collide
Among seismic waves, the S wave arrives before the P wave
② Mantle convection is the driving force that moves the plates
1
Plates move due to the convection of the mantle, so ② is correct.
2
The thickest layer is the mantle (①), the outer core is liquid (③), at a divergent boundary plates separate (④), and the P wave arrives before the S wave (⑤).
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