C925 Earth: Inside and Out
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Free C925 Earth: Inside and Out Questions
1. Which type of weathering breaks rocks into smaller pieces without changing their chemical composition?
- Chemical weathering
- Biological weathering
- Mechanical weathering
- Oxidation
Explanation
Mechanical weathering, also known as physical weathering, disintegrates rocks into smaller fragments through processes like frost wedging, thermal expansion, root wedging, and abrasion, all without altering the mineral makeup of the rock. For example, water freezing in cracks expands by 9%, prying the rock apart, or daily heating and cooling in deserts causes outer layers to peel off in a process called exfoliation. These actions increase surface area for future chemical attack but leave the original minerals chemically unchanged.
2. What should you do immediately when the ground begins shaking during an earthquake indoors?
- Run outside
- Stand in a doorway
- Drop, cover, and hold on
- Lie flat on the floor
Explanation
The universally recommended safety action during earthquake shaking is “Drop, Cover, and Hold On.” You drop to the ground to avoid falling, take cover under a sturdy desk or table to protect your head and neck from falling objects, and hold on until the shaking stops. This technique, promoted by FEMA, USGS, and the Earthquake Country Alliance, has saved countless lives by minimizing injury from collapsing furniture, ceiling fixtures, and flying debris in modern buildings.
3. Which silicate mineral group makes up over 90% of Earth’s crust?
- Olivine
- Pyroxene
- Feldspar
- Quartz
Explanation
Feldspar is the most abundant group of minerals in Earth’s crust, comprising approximately 60% of its volume, which pushes the total silicate mineral content above 90% when combined with quartz, mica, and amphibole. Feldspars are framework silicates with a three-dimensional network of silica tetrahedra linked by aluminum, potassium, sodium, or calcium ions. They weather to form clay minerals and are essential components of igneous, metamorphic, and sedimentary rocks worldwide.
4. During deep-sea drilling in the central Pacific, scientists recover a sequence of oceanic crust that shows normal magnetic polarity for the first 2 million years, then reversed polarity for the next 1.5 million years, followed by normal again; what phenomenon recorded in the cooling basalt explains this striped pattern visible on magnetic anomaly maps of the seafloor?
- Magnetic declination
- Polar wander
- Geomagnetic reversal
- Secular variation
Explanation
Geomagnetic reversal occurs when Earth’s magnetic field completely flips polarity every few hundred thousand years on average. As new oceanic crust forms at mid-ocean ridges, iron minerals align with the current field before locking in as the rock cools, creating symmetrical bands of normal and reversed magnetization that serve as a magnetic tape recorder of seafloor spreading since the Jurassic.
5. Which metamorphic rock displays strong foliation with visible mineral banding?
- Marble
- Quartzite
- Gneiss
- Slate
Explanation
Gneiss forms under high-grade regional metamorphism where intense heat and directed pressure cause minerals to segregate into alternating light and dark bands, creating a distinctive banded appearance. Original rocks such as granite or shale recrystallize, with light bands typically rich in quartz and feldspar and dark bands containing biotite or hornblende. This pronounced foliation and banding make gneiss easily recognizable among metamorphic rocks.
6. Which sedimentary rock forms from compacted clay particles smaller than 1/256 mm?
- Sandstone
- Limestone
- Conglomerate
- Shale
Explanation
Shale is a fissile sedimentary rock formed when clay and silt particles settle in quiet water environments like lakes or deep ocean floors, then compact under overlying sediment. The extremely small grain size gives shale its smooth feel and ability to split into thin layers along bedding planes, making it the most abundant sedimentary rock on Earth’s continents.
7. Which groundwater contamination source comes from agricultural runoff containing nitrates and pesticides?
- Septic tanks
- Landfills
- Non-point source
- Industrial spills
Explanation
Non-point source pollution originates from diffuse areas like fertilized fields and livestock operations, where rainfall washes excess nutrients and chemicals into streams and aquifers. Unlike single-point sources, it is difficult to trace and control, causing widespread algal blooms and drinking-water issues.
8. Which mineral is used as the standard for hardness 7 on the Mohs scale?
- Quartz
- Topaz
- Corundum
- Diamond
Explanation
Quartz, composed of silicon dioxide (SiO₂), defines hardness 7 because it scratches all minerals below it and is scratched by all above it. Its conchoidal fracture, lack of cleavage, and presence in nearly every rock type make it one of the most common and useful reference minerals for field identification.
9. Which type of weathering involves the breakdown of minerals through chemical reactions with water or gases?
- Mechanical weathering
- Physical weathering
- Chemical weathering
- Abrasion
Explanation
Chemical weathering transforms rock minerals into new compounds through reactions such as hydrolysis, oxidation, carbonation, and dissolution. A classic example is feldspar reacting with acidic rainwater to form clay minerals and dissolved ions, or iron oxidizing to rust-colored hematite. In tropical regions, intense chemical weathering can completely dissolve limestone, creating karst landscapes with caves and sinkholes over thousands of years.
10. Which boundary marks the division between the mantle and outer core?
- Moho
- Conrad
- Gutenberg discontinuity
- Lehmann discontinuity
Explanation
The Gutenberg discontinuity is the seismic boundary approximately 2,900 km deep where the solid mantle ends and the liquid outer core begins. Here, P-wave velocity drops sharply and S-waves disappear entirely, proving the outer core is molten. Named after seismologist Beno Gutenberg, this boundary plays a crucial role in understanding Earth’s internal heat engine and magnetic field generation.
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