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Related Experiment Video

Updated: Jul 12, 2026

Laboratory Simulation of an Iron(II)-rich Precambrian Marine Upwelling System to Explore the Growth of Photosynthetic Bacteria

Laboratory Simulation of an Iron(II)-rich Precambrian Marine Upwelling System to Explore the Growth of Photosynthetic Bacteria

Published on: July 24, 2016

Iridium anomaly approximately synchronous with terminal eocene extinctions.

W Alvarez, F Asaro, H V Michel

Science (New York, N.Y.)

|May 21, 1982

Summary

An iridium anomaly and microtektites suggest a major bolide impact occurred 34 million years ago. This event likely caused simultaneous iridium deposition and mass extinctions in radiolarians and mammals.

Area of Science:

Geochemistry
Paleontology
Impact Cratering Studies

Background:

Iridium anomalies are linked to extraterrestrial impacts.
Microtektites found in Caribbean Sea cores (DSDP site 149) are associated with the North American tektite field, dated to ~34 million years ago.
This microtektite horizon coincides with the extinction of five radiolarian species.

Purpose of the Study:

To investigate the cause of an iridium anomaly found at a microtektite layer.
To explore the link between the iridium anomaly, microtektites, and potential mass extinction events.

Main Methods:

Analysis of deep-sea core samples from Deep Sea Drilling Project site 149.
Geochemical analysis for iridium concentration.
Correlation of microtektite layers with known geological and paleontological data.

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Main Results:

An iridium anomaly was detected in coincidence with the microtektite level.
Iridium is likely from a dust cloud deposited simultaneously with microtektites, suggesting a bolide impact.
The impact event is dated to approximately 34 million years ago.

Conclusions:

The iridium anomaly, tektites, and microtektites provide strong evidence for a major bolide impact event 34 million years ago.
This impact may have triggered the extinction of radiolarian species and contributed to mass extinctions in terrestrial mammals.