Science Quarter 4 Review Notes

eScience 6 Lecture Notes

1. Plate Tectonic Theory and Tectonic Plate Boundaries

Plate Tectonic Theory

• The Earth's crust is divided into large, rigid plates that float on the semi-molten layer of the mantle.

• These plates are in constant motion due to convection currents in the mantle.

• This movement causes the formation of mountains, earthquakes, and volcanic activity.

Tectonic Plate Boundaries

1. Divergent Boundaries – Plates move apart, creating new crust (e.g., Mid-Atlantic Ridge).

2. Convergent Boundaries – Plates collide, leading to mountain formation or subduction (e.g., Himalayas, Marianas Trench).

3. Transform Boundaries – Plates slide past each other, causing earthquakes (e.g., San Andreas Fault in California).

2. Earthquakes

What is an Earthquake?

• A sudden shaking of the Earth's surface caused by the movement of tectonic plates.

• Energy is released in the form of seismic waves.

Causes of Earthquakes

• Movement along fault lines.

• Volcanic activity.

• Human activities like mining and reservoir-induced seismicity.

Parts of an Earthquake

• Focus (Hypocenter) – The point underground where the earthquake starts.

• Epicenter – The point on the Earth's surface directly above the focus.

• Seismic Waves – The energy waves that cause shaking.

Measuring Earthquakes

• Richter Scale – Measures the magnitude (strength).

• Mercalli Scale – Measures intensity (damage).

3. Volcanoes

What is a Volcano?

• An opening in the Earth's crust where magma, gases, and ash escape.

Types of Volcanoes

1. Active – Currently erupting or likely to erupt (e.g., Mayon Volcano).

2. Dormant – Not currently erupting but may in the future.

3. Extinct – No recorded eruptions in history.

Parts of a Volcano

• Magma Chamber – Stores molten rock.

• Vent – The opening where magma escapes.

• Crater – A bowl-shaped depression at the top.

• Lava – Molten rock that reaches the surface.

Effects of Volcanic Eruptions

• Positive: Fertile soil, geothermal energy, formation of new land.

• Negative: Destruction of property, loss of life, climate change.

4. Earth's Motion

a. Rotation

• The Earth spins on its axis, completing one full turn in 24 hours.

• Causes day and night.

• The Earth rotates west to east.

b. Revolution

• The Earth orbits around the Sun in 365 ¼ days.

• Causes seasons.

• The Earth's tilted axis (23.5°) affects sunlight distribution.

5. Solar System

The Sun

• A massive star that provides heat and light.

• The center of the Solar System.

Planets in Order (from the Sun)

1. Mercury – Smallest and closest to the Sun.

2. Venus – Hottest planet due to thick atmosphere.

3. Earth – The only planet known to support life.

4. Mars – Known as the Red Planet.

5. Jupiter – Largest planet with a Great Red Spot.

6. Saturn – Has beautiful rings made of ice and rock.

7. Uranus – Rotates on its side.

8. Neptune – The windiest planet.

Other Celestial Bodies

• Asteroids – Rocky objects in the asteroid belt.

• Comets – Made of ice and dust with a glowing tail.

• Meteoroids – Space rocks that burn up as meteors (shooting stars).