History's Warning

By Robert Monroe

1 | 2

Continued...

The rocks from Twisted Sister promise to contribute to reconstructing the events of the PETM. The case for the PETM being the trigger that transitioned the Earth from one geologic epoch to another has only developed in the last decade. Most of what is inferred about it comes from ocean floor and terrestrial sediments, two sources that come with limitations. Sediment accumulates steadily on the seafloor at a rate of roughly one centimeter per millennium, leaving researchers interested in time scales smaller than 1,000 years with little detail with which to work.

Norris and graduate student Johnnie Lyman, a co-leader of this trip, have been part of efforts in recent years to recover records of PETM both from the seafloor and from terrestrial sources in Wyoming. In these locations, 1,000 years might be represented by a band of rock one meter (3.28 feet) thick, but because of the sporadic way sediment accumulates on land, those results need confirmation from another source.

Cedar Breaks is an ancient lakebed, where deposits collected in steady fashion year after year. Its sediments could help validate land records and provide more detailed samples than the ocean can yield. Lyman is hoping for millennial slices as much as 10 centimeters (3.93 inches) thick but that is only one obstacle to useful data. Somewhere within the sedimentary record of Cedar Breaks is the record of what happened during the PETM. But how does one find it?

Tauxe came with the group to help them read what she calls the "bar code" of the rocks by dating a cross-section of a cliff face below Twisted Sister and from another promising dig site. Throughout Earth's history, the planet's magnetic field has shifted from pole to pole with the compass last pointing south 840,000 years ago. The PETM happens to have taken place during a relatively stable period between two reversals.

The team took rock samples at two-meter (6.56-foot) intervals from a 200-meter (656-foot) section of cliff. Norris collected another batch of rocks at even narrower intervals within that same section. Lyman's first analytical task was to look for relative quantities of carbon and oxygen isotopes, the echo left behind by the ancient lake's algae and other rudimentary life forms. (VIDEO: Johnnie Lyman describes how lab researchers extract information from ancient rocks) An "excursion," or sudden deviation in carbon isotopes, could be the calling card of the PETM. If she finds the excursion, Lyman will conduct a second round of analysis in which she examines the magnetic properties of the rocks to look for reversals of the Earth's magnetic field. The patterns they form will be plotted against the timeline of known magnetic reversals to confirm whether the team's rocks are in the right historical ballpark.

Norris and Lyman note that there are known key differences between the PETM and today, the most significant being that the world 55 million years ago was hotter to begin with before the event started. But if the rate and amount of the PETM's infusion of carbon into the atmosphere turns out to be comparable to today's, then history's lesson is sobering regardless. Researchers have estimated that 368 gigatons of carbon dioxide were emitted into the atmosphere between 1850 and 1995, with slightly more than half of that being reabsorbed naturally through processes like plant photosynthesis. A United Nations science advisory panel projected that we will be adding another 20 gigatons per year by the year 2100 if trends continue for a total input of 2,368 gigatons since the start of the industrial revolution.

With such comparable numbers, Norris believes the ancient event could well serve as an instructive precedent of climatic upheaval. But even in its aftermath, there could be another parallel, he said. There is evidence that foraminifera were able to come back from even such a destabilizing event in as few as 10,000 years because of a variety of factors that made them adaptable, an apparent affirmation of one of Darwin's most basic observations about survival. (VIDEO: Richard Norris talks about the potential lessons we can derive from the story of the Paleocene-Eocene Thermal Maximum)

Indeed, a possibly encouraging aspect of the PETM is that, with the exception of the deep sea, there were few extinctions on land or in the surface ocean despite the intense global warming. Evidently, the combination of ocean acidification and warming was not enough to tip most species over the brink of extinction. On the other hand, Norris notes, it is possible that humans will end up burning the roughly 5,000 gigatons of carbon locked in all the coal and oil reserves known and create a dire set of conditions.

"If we don't get our fossil fuel diet under control, the PETM will not be much comfort as a predictor of the effects on the Earth's climate," Norris said. "We will have stepped well into the unknown with a rapid carbon release more the twice the size of any event currently known from Earth's history."

1 | 2

Podcast
Audio | Video | Subscribe
Video
High | Low
Slideshow
Download PDF

Cedar Breaks National Monument
The Paleogene Period
Paleocene mammals of the world

•