Science: Conflicting Viewpoints Flashcards

What is the central claim of Scientist 1? (Passage: Scientist 1: The extinction was caused by the impact of a large asteroid... The discovery of a worldwide layer of iridium... is the key evidence. Scientist 2: While an asteroid impact did occur, it was not the primary cause. The extinction was a more gradual process driven by massive volcanic activity...)

Answer: A single, catastrophic asteroid impact was the primary cause of the mass extinction.

Scientist 1's entire argument is built around the idea of a singular, catastrophic event. The key evidence cited—the iridium layer and the Chicxulub crater—both point to a massive asteroid impact as the direct and primary cause of the mass extinction.

Which of the following assertions would both Scientist 1 and Scientist 2 agree with?

Answer: A layer of iridium exists at the Cretaceous-Paleogene boundary.

Scientist 1 states that the 'discovery of a worldwide layer of iridium... is the key evidence.' Scientist 2 acknowledges this evidence but offers an alternative explanation for it, stating 'The iridium layer could have been sourced from the Earth's mantle.' Therefore, both agree that the layer exists.

What is the fundamental point of disagreement between the two scientists?

Answer: Whether the primary cause of extinction was a sudden event or a gradual process.

The core of the conflict is the primary mechanism of extinction. Scientist 1 argues for a sudden, external event (impact), while Scientist 2 argues for a long-term, internal process (volcanism). All other disagreements, such as the source of the iridium, stem from this central conflict.

Which of the following discoveries, if true, would most strongly support the hypothesis of Scientist 2?

Answer: Fossil records show a significant, steady decline in species diversity for a million years leading up to the iridium layer.

Scientist 2's hypothesis is based on a 'gradual process' that 'stressed ecosystems to a breaking point long before the asteroid impact.' Finding evidence of a slow decline in biodiversity before the impact event would directly support this claim of a gradual, long-term cause rather than a single, sudden catastrophe.

According to Scientist 1, the iridium layer is significant because:

Answer: Iridium is rare on Earth's surface but is abundant in asteroids.

Scientist 1 explicitly states that iridium is 'an element rare on Earth but common in asteroids.' This is the crucial link in the argument: the presence of an element common in asteroids, found in a worldwide layer at the exact time of the extinction, serves as the primary evidence for an asteroid impact.

Scientist 2's explanation for the iridium layer is that it:

Answer: Was brought to the surface from the Earth's mantle by volcanoes.

Scientist 2 directly challenges Scientist 1's interpretation of the iridium layer. The last sentence of Scientist 2's viewpoint offers an alternative source: 'The iridium layer could have been sourced from the Earth's mantle via these volcanic plumes.'

The discovery that the specific isotopic ratio of iridium in the boundary layer perfectly matches that of known asteroids and is distinctly different from mantle-derived iridium would most damage the viewpoint of:

Answer: Scientist 2, because it would invalidate the proposed volcanic source for the iridium.

This discovery would directly refute Scientist 2's alternative explanation for the iridium layer. If the iridium's 'fingerprint' matches asteroids and not the mantle, it invalidates the claim that volcanoes were the source, thereby significantly weakening the overall argument of Scientist 2.