Science- The Earth's Layers

Earth is a dynamic planet, constantly changing due to both internal and external forces.

The dynamics of the Earth are shaped by a multitude of factors, among which are:

• The planet's geological composition and unique characteristics play a significant role.

Geological composition:

• Includes its crust, mantle, core, and the distribution of its tectonic plates, volcanic activity, and seismic events

2 Layers of the Earth

• Compositional- What it is made of

• Mechanical- How the Earth behaves

Compositional Layers:

• Crust- Outermost, thinnest layer (5–70 km thick)

  • Continental Crust: thick, less dense, made of granite

  • Oceanic Crust: thin, dense, made of basalt

  • Composed mostly of silicon (Si), oxygen (O), aluminum (Al)

  • Makes up less than 1% of Earth’s mass

• Mantle- Extends from the base of the crust to 2,900 km deep

  • Largest layer by volume (84%)

  • Composed of silicate rocks rich in magnesium (Mg) and iron (Fe)

  • Solid, but flows slowly

• Outer Core

  • Liquid, and its motion creates Earth's magnetic field

  • Composed mainly of liquid iron and nickel

• Inner Core

  • Solid, due to the immense pressure despite extreme heat

  • Made mostly of solid iron and nickel

Mechanical Layers:

• Litosphere- the outermost mechanical layer

  • Consisting of the crust and the uppermost part of the mantle

  • The average thickness of the lithosphere is about 80 km, but varies

    depending on whether it is under oceans or continents.

  • It behaves like solid, brittle rock and is divided into tectonic plates that float on the underlying layers

• Asthenosphere- located beneath the lithosphere

  • although it is solid, the high temperatures allow it to flow slowly over geological timescales. This layer is crucial for the movement of tectonic plates above it.

  • is a soft, ductile layer of the upper mantle

• Mesosphere- lower mantle, lies beneath the asthenosphere

  • characterized by high pressure and temperature, which make it rigid despite being composed of solid silicate materials.

Ring Of Fire

• A vast horseshoe- shaped zone around the Pacific Ocean, approximately 25,000 miles (40,000 km) long and up to 500 km wide

• 75% of Earth's active volcanoes and 90% of the world's earthquakes are located here

Plate Boundaries

• The edges where two or more tectonic plates meet.

• They are zones of intense geological activity, such as earthquakes, volcanic eruptions, and mountain building, caused by the movement and interaction

Mountain Belts

• Are long, continuous chains of mountains that stretch across large regions of the Earth, often thousands of kilometers.

• They usually form along convergent plate boundaries where tectonic plates collide, causing the Earth’s crust to fold, fault, and uplift.

What is an Earthquake

• Sudden shaking of Earth’s surface

• Energy release in rocks

• Seismic waves

Causes of an Earthquake

• Tectonic plate movement

• Fault stress

• Volcanic activity

• Human activities

Parts of an Earthquake

• Fault (fracture line)

• Epicenter (surface point above focus)

• Focus/ Hypocenter (underground origin)

• Seismic Waves

  • Body Waves- travel through the Earth's interior

  • Surface waves- travel along the Earth's surface and are more destructive during earthquakes.

Body Waves

• P-Waves (Primary Waves):

  • These are the fastest seismic waves and can travel through solids, liquids, and gases.

  • They cause particles to move in the same direction as the wave, leading to compressions and expansions

• S-waves (Secondary Waves):

  • These waves are slower than P-waves and can only travel through solids.

  • They cause particles to move perpendicular to the direction of wave propagation, resulting in a shearing motion.

Surface Waves

• Love waves

  • These cause horizontal motion and are faster than Rayleigh waves.

  • Named after A.E.H. Love or Augustus Edward Hough Love, a British mathematician (1911).

• Rayleigh waves:

  • These create an elliptical motion, similar to ocean waves, and are usually the most damaging type of seismic wave.

  • Named after Lord Rayleigh (John William Strutt), a British physicist (1885).

How Earthquakes get measured

• Seismograph

  • Instrument that records earthquake waves

• Seismogram

  • Traces of amplified, electronically recorded ground motion made by seismographs

What makes an Earthquake dangerous?

• Collasped Buildings and Bridges

• Ruptured gas pipelines & other infastructure

• trigged landslides (liquefaction), volcanoes, tsunamis

Magnitude Levels of an Eathquake

• Magnitude 0–1 (Micro) Micro-earthquakes. These are so small that people cannot feel them. Only sensitive instruments like seismographs can detect them.

• Magnitude 2–3 (Minor) Very small earthquakes. People may not feel them, but they are recorded by instruments. Sometimes felt like a light vibration if you are near the epicenter.

• Magnitude 4 (Light) Now the shaking can be felt indoors, like a heavy truck passing by. Usually causes no damage.

• Magnitude 5 (Moderate) Shaking is stronger. Some objects may fall, windows may rattle, and weak structures can be damaged

• Magnitude 6 (Strong) Buildings and houses can be damaged. It is strong enough to be dangerous, especially near the epicenter.

• Magnitude 7 (Major) This is a major earthquake. Severe damage occurs to poorly built buildings. It can be destructive across a wide area.

• Magnitude 8 (Great) A truly great earthquake. Many buildings collapse, roads and bridges are destroyed. Tsunamis may be generated. Affects hundreds of kilometers.

• Magnitude 9 (Rare, Catastrophic) Extremely rare. Causes massive destruction over very large areas. An example is the 2011 Japan earthquake, which was magnitude 9.0 and triggered a huge tsunami.

• Magnitude 10 (Theoretical Maximum) This is the strongest possible earthquake, but none has ever been recorded in history. It would cause unimaginable global damage.