Moon Formation, Earth Tectonics, and Sound Waves
Formation of the Moon
Scientists believe that planets, including those in our solar system, originate from grains of dust. Gravity and other forces cause the dust to combine, ultimately forming planets.
The Sun, planets, moons, and asteroids are thought to have formed around the same time, approximately 4.5 billion years ago, from a nebula.
Solar Nebula Hypothesis
- Planets form from dust grains.
- Gravity causes dust to coalesce.
Nebulae and Moon’s Formation
Collision Theory:
- Collision of a large body with Earth.
- Ejected debris forms the Moon.
- The Moon’s interior becomes molten.
- The Moon’s surface cools, and the crust forms; smaller impacts create craters.
- Large impacts create basins.
- Basins flood with lava, creating maria.
Tectonics
Earth’s Layers
- Crust:
- Thinnest layer of the Earth.
- Between 8 – 40 km thick.
- Thinner under the ocean than on land.
- Contains rocks and minerals.
- Mantle:
- Thickest layer of the Earth.
- Made of solid rock that can flow (plastic rock).
- Moves in large circles caused by convection currents.
- Hot rock rises, and cold rock sinks.
- Outer/Inner Core:
- Mainly made of iron and nickel.
- The outer core is liquid.
- The inner core is hotter, but metals are solid.
- The outer core is where the magnetic field originates (making compasses work!).
Continental Drift
- The continents have not always been in their current positions.
- They are believed to have drifted into position and continue to drift.
- This is caused by the movement of the Earth’s tectonic plates.
Convection Current in the Mantle
- The inner part of the mantle receives thermal energy from the core.
- The fluid in the mantle expands when heated, becoming less dense than the surrounding fluid.
- This hotter, less dense fluid rises towards the crust, cools, and sinks, creating a convection current.
Key Terms
- Continent: One of the seven large landmasses on Earth.
- Country: A smaller part of a continent.
- Continental drift: The study of the movement, collision, and division of continents.
- Sedimentary rock: Rocks made from layers of sediment and deceased organisms.
- Igneous rock: Rocks formed from cooled and solidified magma.
- Metamorphic rock: Rocks transformed from existing rocks under extreme pressure.
Alfred Wegener
- Alfred Wegener first proposed the idea of continental drift, but it was initially dismissed.
- He noted that some continents seem to fit together like jigsaw-puzzle pieces.
- However, he couldn’t explain the mechanism behind it.
- Fifty years later, new evidence was discovered, leading to the theory of plate tectonics and supporting Wegener’s theory.
Interference of Sound
- When two waves meet, the effect is called interference.
- Interference can only occur between waves of the same type (e.g., both sound waves or both water waves).
- When two waves interfere, they can reinforce or cancel each other out.
Sound and Space
Loudness and Amplitude
- Amplitude affects the loudness of a sound.
- A large amplitude means the sound is loud.
- A small amplitude means the sound is quiet.
Measuring Pitch
- All sound is created by vibrations and travels as waves.
- High-pitched sounds vibrate more rapidly than low-pitched sounds.
- One wave (or oscillation) is the distance between the peak of one wave and the next.
Frequency
- The number of waves (or oscillations) per second is the frequency of the wave.
- Higher-pitched sounds have higher frequencies.
- Lower-pitched sounds have lower frequencies.
- Frequency is measured in hertz (Hz). (1 Hz means one wave passes every second.)
- The amplitude of a vibration is the greatest distance the object is from its rest position.
Pitch and Loudness
- Pitch refers to how high or low a note is on a musical scale. It can be very quiet or very loud; its pitch remains constant.
- Loudness is the intensity of a sound, linked to the energy of the sound source.