grade 7 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. The P and S wave drawing is on the next volcanoes-and-earthquakes chapter. Press the buttons to switch among the three boundary types and the landforms appear.

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

Earthquake vs Volcano Comparison

Aspect	Earthquake	Volcano
Cause	Plate collision/sliding	Magma eruption
Location	Plate boundary (fault)	Convergent/divergent boundary
Result	Ground shaking	Lava and ash eruption
Measurement	Richter magnitude	Volcanic 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

⑤Speed order: P > S > surface waves

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?

From the outside in, the inside of the Earth is crust → mantle → outer core → inner core.

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?

A boundary where plates collide is called a convergent boundary.

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?

①The thickest layer of the Earth is the crust

②Mantle convection is the driving force that moves the plates

③The outer core is in a solid state

④At a divergent boundary, two plates collide

⑤Among seismic waves, the S wave arrives before the P wave

▸ ② Mantle convection is the driving force that moves the plates

Plates move due to the convection of the mantle, so ② is correct.

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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Biological Classification System

Volcanoes & Earthquakes

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