Lecture 1 Flashcards
What is the Nebular Theory for the formation of the Solar System?
The Nebular Theory states that our Solar System formed from a huge cloud of gas and dust (a nebula) left over from previous star cycles. This cloud condensed into a swirling disc, with a dense central ball that became the Sun, while dust in the surrounding rings formed planetesimals (the building blocks of planets).
Why do planets tend to be round rather than irregular in shape?
As planetesimals grow larger, their interior heats up and becomes soft from collisions and radioactive decay. Gravity then pulls the mass into a roughly spherical shape, which lowers the planet’s overall energy state
How did Earth’s interior become layered (differentiated)?
In Earth’s early history, sufficient heat caused iron and other heavy metals to melt and sink toward the center, forming a metallic core, while lighter materials remained closer to the surface as the mantle and crust. This separation process is called differentiation.
What heat sources contributed to Earth’s early heating and melting?
Major heat sources included (1) collisions from incoming objects, (2) radioactive decay of unstable isotopes, and (3) the compression of matter into a smaller volume, all of which raised Earth’s temperature enough to melt interior materials.
How did our Moon form according to the Giant Impact Hypothesis?
Soon after Earth formed, a Mars-sized body collided with it, ejecting debris that went into orbit around Earth. Over time, this debris coalesced to form the Moon
What are the main layers of Earth’s interior by composition and state?
- Crust (solid): ~7–70 km thick
- Mantle (solid): 2885 km thick
- Outer Core (liquid): 2255 km thick
- Inner Core (solid): 1216 km radius
Why is Earth’s outer core liquid while the inner core is solid?
Even though both core layers are iron-rich and extremely hot, the pressure in the inner core is so high that the iron remains solid. In the outer core, the pressure is lower (though still huge) and the temperatures are sufficient to keep iron in a liquid state.
What is the approximate age of the Earth, and how do we know?
Earth is about 4.57 billion years old. Scientists date meteorites (which formed at the same time as the rest of the Solar System) to determine Earth’s age, since Earth’s oldest rocks have largely been recycled by geologic processes.
What types of seismic waves are used to study Earth’s interior?
- P waves (Primary): Compressional waves that travel through solids, liquids, and gases.
- S waves (Secondary): Shear waves that can only travel through solids.
Why do S waves not travel through the outer core?
Because S waves need a solid medium to propagate. The outer core is liquid, so S waves stop when they reach it, creating an S-wave “shadow zone.”
How does seismic tomography resemble a medical CT scan?
Just like a CT scan uses multiple X-rays from different angles to build a 3D image of the body, seismic tomography uses seismic waves traveling at various angles through Earth to create a 3D model of the interior (e.g., density variations, velocity differences)
Besides seismic waves, what other evidence helps us understand Earth’s interior?
- High-pressure experiments using devices like diamond-anvil cells to mimic the extreme conditions of Earth’s core.
- Meteorites, which provide samples analogous to Earth’s mantle (stony) or core (iron).
- Volcanic rocks such as kimberlites that bring fragments of mantle material (xenoliths) to the surface.
What are kimberlites, and why are they important to geologists?
Kimberlites are volcanic rocks that erupt very quickly from deep in the mantle, often carrying up pieces of mantle rock (xenoliths) and diamonds. They give us direct samples of Earth’s upper mantle
What are the three main compositional layers of Earth if we group crust and mantle together?
- Crust + Mantle (rocky silicates)
- Outer Core (liquid iron and nickel)
- Inner Core (solid iron and nickel)
What is the difference between a planetesimal and a proto-Earth?
A planetesimal is an early, smaller, irregular precursor (< ~500 km) that formed from dust and rock in the protoplanetary disc. A proto-Earth is a much larger body that formed when planetesimals merged and gained enough mass for internal heat and differentiation to occur.
In the early Solar System, why did heavier elements like iron concentrate in Earth’s center?
As Earth’s interior heated and melted, denser metals (e.g., iron) sank toward the center under the force of gravity, forming the metallic core. Lighter elements remained nearer the surface.
What is radioactive decay, and how does it contribute to Earth’s heat budget?
Radioactive decay is the breakdown of unstable isotopes, releasing heat. This continuous process contributes significantly to Earth’s internal heat, sustaining processes such as mantle convection
Why do geologists use meteorites to estimate Earth’s age rather than Earth rocks?
Earth’s surface rocks have been reworked by plate tectonics, erosion, and metamorphism, so they rarely preserve truly ancient material. Meteorites formed at the same time as Earth, but remained largely unchanged, giving a more reliable record of Solar System history
What is the approximate radius of Earth from its surface to the center?
Earth’s total radius is about 6,371 km, from the surface down to the center of the core.
