The half-life of C-14 is 5470 years. If a particular archaeological sample has one-quarter of its original radioactivity remaining, what is the best estimate for its age?

Question

The law of superposition states that, in horizontal layers of sedimentary rock, each layer is:
Younger than the layer above it and older than the layer below it.
Neither older nor younger than the other layers.
Older than the layer above it and younger than the layer below it.
Always older than any vertical layers.
3. On March 20, 1980, Mount St. Helens experienced a magnitude 4.2 earthquake; and on March 27, steam venting started. By the end of April, the north side of the mountain had started to bulge. On May 18, a second earthquake, of magnitude 5.1, triggered a massive collapse of the north face of the mountain. The magma in St. Helens burst forth into a large-scale flow that flattened vegetation and buildings over 230 square miles around.
What geological impact did the 1980 eruption of Mt. St. Helen's (pictured below) have on the mountain and its surrounding environment. Select all that apply.
Vegetation populations thrived.
The summit height was reduced.
Vegetation was flattened due to debris avalanche.
The summit height was increased.
The eruption has no geological impacts.

4. The diagram to the right represents a cross section of a portion of the Earth’s crust showing four different rock layers, A, B, C, D. Which rock layer shows the greatest evidence of erosion?

5. Which of the following is a renewable resource?
Wind
Coal
Natural gas
Oil

Answer 1

1. Estimation of Age of Archaeological Sample: The half-life of Carbon-14 (C-14) is 5,470 years. If a sample has one-quarter of its original radioactivity remaining, it means that two half-lives have passed (after one half-life, half remains; after two half-lives, one-quarter remains). Thus, 2 half-lives = 2 × 5,470 years = 10,940 years. Therefore, the best estimate for the age of the sample is 10,940 years.

2. Law of Superposition: According to the law of superposition, each layer of sedimentary rock is younger than the layer above it and older than the layer below it.

3. Geological Impact of the 1980 Eruption of Mt. St. Helens: The following geological impacts are applicable:

   • The summit height was reduced.
   • Vegetation was flattened due to debris avalanche. The other options do not accurately reflect the geological impacts of the eruption.

4. Greatest Evidence of Erosion: To determine which rock layer shows the greatest evidence of erosion, one would typically look for a layer that has been significantly worn down, appears uneven, or has a thinner profile compared to adjacent layers. Without a specific diagram to view, I cannot definitively answer based on numerical identifiers (A, B, C, D). Generally, erosion would be evidenced by areas where material appears to have been removed or weathered significantly.

5. Renewable Resource: The renewable resource from the options provided is Wind. The other options—Coal, Natural gas, and Oil—are non-renewable resources.