AZSCI Earth and Space Science 2 — Questions and Answers
Question 1: A research vessel mapping a section of the Atlantic seafloor equidistant from the Mid-Atlantic Ridge discovers a series of magnetic stripes in the basaltic rock. Stripe A, located 10 km west of the ridge, shows normal polarity. Stripe B, located 10 km east of the ridge, also shows normal polarity. Stripe C, at 15 km west, shows reversed polarity. Which of the following is the most advanced conclusion that can be drawn from this specific data pattern?
- The age of the seafloor at Stripe A and Stripe B is virtually identical, and both are younger than the seafloor at Stripe C. (Correct answer)
- The Earth's magnetic field has reversed multiple times in the past.
- New oceanic crust is continuously formed at the Mid-Atlantic Ridge.
- The rate of seafloor spreading is faster on the west side of the ridge than on the east side.
Correct answer: The age of the seafloor at Stripe A and Stripe B is virtually identical, and both are younger than the seafloor at Stripe C.
The symmetric pattern of magnetic anomalies (stripes) on either side of a mid-ocean ridge is key evidence for seafloor spreading. Since Stripes A and B are equidistant from the ridge and have the same polarity, they must have formed at the same time. Stripe C is farther away, meaning it formed earlier and has been pushed outward. Therefore, A and B are the same age, and both are younger than C.
Question 2: While all Milankovitch cycles contribute to long-term climate change, scientists believe the ~41,000-year cycle of obliquity (axial tilt) was the dominant driver of ice ages between one and three million years ago. What is the primary reason that changes in obliquity are considered so critical for initiating glaciation?
- It alters the total amount of solar energy the Earth receives annually.
- It changes the length of the seasons, making winters significantly longer.
- It primarily affects the intensity of solar radiation received at high latitudes during the summer. (Correct answer)
- It causes the timing of the seasons (e.g., summer solstice) to shift over a 23,000-year period.
Correct answer: It primarily affects the intensity of solar radiation received at high latitudes during the summer.
The initiation of an ice age is highly dependent on whether snow and ice from the winter can survive the summer melt. Obliquity, or the tilt of the Earth's axis, directly impacts the intensity of the seasons. A lower axial tilt results in less direct solar radiation at the poles during the summer, leading to cooler summers where ice sheets can persist and grow. This effect on high-latitude summer insolation is considered a critical trigger.
Question 3: A paleontologist discovers a fossil of a snail. The original shell material has completely dissolved, but the sediment that filled the inside of the shell has hardened, creating a detailed replica of the snail's internal chambers. This type of fossil is best classified as what?
- An external mold
- A permineralized fossil
- A cast
- A steinkern (internal mold) (Correct answer)
Correct answer: A steinkern (internal mold)
A steinkern, or internal mold, is formed when sediment or minerals fill the internal cavity of an organism, such as a shell, and then harden. If the original shell later dissolves, the steinkern remains, preserving the shape of the organism's interior. A standard cast would fill an external mold, replicating the outer surface, not the internal chambers.
Question 4: A geoscientist is using dendrochronology to date ancient wooden beams from a ruin in a region known for frequent droughts and insect infestations. Which of the following represents the most significant potential challenge to establishing an accurate, absolute timeline for the ruin?
- The presence of sapwood on some of the beam samples.
- The possibility of missing or 'false' rings caused by environmental stress. (Correct answer)
- The need to calibrate the tree-ring data with radiocarbon dating.
- The wood being from a species, like oak, that is commonly used for this technique.
Correct answer: The possibility of missing or 'false' rings caused by environmental stress.
While all are aspects of dendrochronology, the most significant challenge to accuracy in this stressful environment is the potential for anomalous ring growth. Severe drought or insect defoliation can cause a tree to fail to produce a ring in a given year (a missing ring) or produce multiple, less-distinct rings (false rings). These anomalies can lead to incorrect cross-matching and an inaccurate timeline if not carefully accounted for.
Question 5: Seismograph stations around the globe record data from a major earthquake. Stations located more than 104° away from the epicenter detect P-waves, but not S-waves, that traveled through the Earth's interior. What does this 'S-wave shadow zone' fundamentally imply about Earth's structure?
- The Earth's inner core is solid.
- The mantle is rigid and transmits both wave types.
- The Earth's outer core is a liquid. (Correct answer)
- Seismic waves are refracted at the Moho discontinuity.
Correct answer: The Earth's outer core is a liquid.
S-waves (shear waves) are a type of seismic wave that can only propagate through solid materials; they cannot travel through liquids. The fact that S-waves are blocked and do not appear at seismographs on the opposite side of the Earth from an earthquake's focus demonstrates that there is a liquid layer deep within the Earth. This layer is the outer core.
Question 6: In the arid climate of the Sonoran Desert in Arizona, daytime temperatures can be extremely high while nighttime temperatures drop dramatically. Which of the following best explains this large diurnal temperature range as it relates to atmospheric composition?
- The high concentration of atmospheric dust radiates heat effectively at night.
- The low atmospheric pressure at desert altitudes cannot hold heat.
- The lack of significant water vapor in the atmosphere allows for rapid radiative heating and cooling. (Correct answer)
- The high albedo of the light-colored desert sand reflects most solar energy back into space.
Correct answer: The lack of significant water vapor in the atmosphere allows for rapid radiative heating and cooling.
Water vapor is a powerful greenhouse gas that absorbs and re-radiates thermal energy. In humid regions, water vapor in the air traps outgoing longwave radiation, keeping nighttime temperatures warmer. In arid regions like Arizona, the low humidity means there is very little water vapor to trap this heat. As a result, the ground heats up very quickly during the day (rapid heating) and radiates that heat away just as quickly into space after sunset (rapid cooling), leading to a large diurnal temperature range.
AZSCI Earth and Space Science 2
A research vessel mapping a section of the Atlantic seafloor equidistant from the Mid-Atlantic Ridge discovers a series of magnetic stripes in the basaltic rock.
Stripe A, located 10 km west of the ridge, shows normal polarity.
Stripe B, located 10 km east of the ridge, also shows normal polarity.
Stripe C, at 15 km west, shows reversed polarity.
Which of the following is the most advanced conclusion that can be drawn from this specific data pattern?