Geologists studying ice cores from Antarctica have identified layers containing volcanic ash from eruptions occurring up to 800,000 years ago. Each layer's chemical composition can be matched to specific eruptions, providing a precise timeline. By correlating ash layers found in widely separated cores, researchers can synchronize climate records from multiple sites to within a few years.
Which choice most logically completes the text? The passage suggests that volcanic ash layers serve as _______
- A
obstacles that complicate the dating of polar ice
- Bcheck_circle
temporal markers that allow comparison across geographically distant climate records
- C
the primary cause of climate change recorded in ice cores
- D
evidence that climate has remained constant over 800,000 years
Explanation
Synchronization across sites makes ash layers temporal markers. A is unsupported; C confuses correlation with cause; D contradicts the helpful role described.