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Extraterrestrial cause for the cretaceous-tertiary extinction.
Science (New York, N.Y.)
|June 6, 1980
Summary
An asteroid impact 65 million years ago likely caused the Cretaceous-Tertiary extinctions. This impact explains high iridium levels found in sediments worldwide, supporting the extraterrestrial impact hypothesis.
Area of Science:
- Geochemistry
- Paleontology
- Planetary Science
Background:
- Platinum group elements, like iridium, are rare in Earth's crust.
- Elevated iridium concentrations in deep-sea sediments suggest extraterrestrial material influx.
- The Cretaceous-Tertiary (K-T) boundary, 65 million years ago, marks a mass extinction event.
Purpose of the Study:
- To investigate the origin of iridium anomalies at the K-T boundary.
- To test the hypothesis that an asteroid impact caused the K-T extinctions.
- To correlate extraterrestrial material influx with mass extinction events.
Main Methods:
- Analysis of iridium concentrations in deep-sea limestone sediments from Italy, Denmark, and New Zealand.
- Comparison of iridium levels at the K-T boundary with background levels.
- Chemical analysis of boundary clay and surrounding limestone layers.
Main Results:
- Significant iridium increases (30-160x background) were found at the K-T boundary in multiple locations.
- The iridium is confirmed as extraterrestrial in origin, not from a supernova.
- Boundary clay composition differs markedly from Cretaceous and Tertiary limestones, supporting a dust-derived origin.
Conclusions:
- A large asteroid impact (estimated diameter 10 +/- 4 km) is the most plausible cause for the K-T extinctions.
- The impact injected vast amounts of dust into the stratosphere, causing global darkness and suppressing photosynthesis.
- This mechanism aligns with paleontological evidence of mass extinctions and geochemical findings.
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