The Timing and Causes of Mass Extinctions

Could there be a human signal in the geological record?

Nuclear power plants could leave evidence of our existence for future civilizations. (Stefan Kühn / Wikimedia)
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Two recent papers, one led by Blair Schoene of Princeton University, the other by Courtney Sprain from the University of California, Berkeley, investigate the causes and timing of the infamous K-T extinction, the one that resulted in the demise of the dinosaurs. The authors conclude that the die-off was due not just to an asteroid impact, but also to the large volcanic eruptions that occurred shortly before and after it. The studies show how important it is to know the exact timing of events during a mass extinction. Such knowledge might even come in handy in understanding the anthropogenic mass extinction happening right now due to the human impact on Earth’s environment.

The anthropogenic signals of a mass extinction is also the subject of a paper by Gavin Schmidt and Adam Frank that just appeared in print in the International Journal of Astrobiology. The intriguing part of this study is that the authors go beyond identifying markers that are expected to be preserved in the geological record, including disruption of carbon and nitrogen cycles, changes in biota, sedimentation and mineralogy, even remnants of technology such as the preservation of certain plastics and radioactive artifacts. Schmidt and Frank go through the last 300-plus million years of the geological record to discern which of the past mass extinctions might have these tell-tale signals.

Of course, the question of whether there might have been an ancient technological civilization on Earth before our own is highly speculative. But the idea has been raised before, including in my Cosmic Zoo book. It’s sometimes called the Silurian hypothesis—perhaps a Doctor Who reference (which may not necessarily help its credibility).

Schmidt’s and Frank’s surprising find is that many similarities can be seen in the geological record between previous extinctions and the current human-caused mass extinction. The disruption in natural cycles and changes in biota, sedimentation and mineralogy are even of comparable magnitude. No plastic has been found, but one might wonder if anyone has really looked. Nor have radioactive enrichments suggestive of nuclear power plants been found in the geological record. The authors do, however, identify one crucial indicator as to whether a mass extinction might be of anthropogenic origin—that is, if it occurs within a short time period.

The development of better technologies to reveal signatures of mass extinctions should help us nail down the timing, and therefore the causes, of these events. Will we find any that happened especially rapidly? If so, we may want to look for evidence of ancient plastic compounds and radioactivity.

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