|
||
History's WarningAn ancient global warming episode drastically changed the planet. Life on Earth needed 200,000 years to recover. What we're headed for in the next century could be even bigger. By Robert MonroeWith frequently slick volcanic mud at its topmost layer and 2,000 feet of crumbly red limestone between the rim and the valley below, the centerpiece amphitheater at Cedar Breaks National Monument can seem like a confection made in hell to hikers. But despite the quality of palpable erosion and instability that has rendered Cedar Breaks a repository of wind- and rain-sculpted rock, the formation is robust in one aspect. It contains what may be the clearest record anywhere on Earth of a rapid climate change event 55 million years ago that could give us the best hint at what climate has in store for us in the next century. Cedar Breaks is the smaller neighbor to Utah's Bryce Canyon National Park, both made famous by their brilliant red sedimentary cliffs and fanciful stone pillars known as hoodoos. More importantly to the Scripps researchers who visited here in September, Cedar Breaks is older, enough so to bear sedimentary rocks formed during the Paleocene-Eocene Thermal Maximum, known as the PETM to geologists.  Sampling vertically up steep ridge faces, the team sought rocks of just the right age to find evidence of the PETM. The PETM was but one of many rapid-warming episodes to have taken place throughout history, but one of the biggest. Existing knowledge suggests that some event, possibly a large-scale melting of seafloor methane deposits, released between 1,200 and 2,500 gigatons of carbon dioxide into the atmosphere. The incident took place in less than 1,000 years. Whether it happened in one year or 50 or 500 is unknown but by the end of the millennium, global temperatures had risen between 4° and 7 ° C (7.2° and 12.6° F). Many climate scientists have speculated about what such a circumstance would look like today but PETM already gives a rough account - little of it encouraging for a planet that now has 6.5 billion human inhabitants. The warming extended to the deep oceans and was enough to reverse global circulation patterns. Chemical evidence shows that the heat created oxygen-starved acidic waters intolerable to many life forms. The presence of acidic water suggests that the outgassing event and subsequent dissolution of CO2 in the water must have happened quickly, too fast for natural processes to absorb the excess carbon Mass die-offs ensued. The acid may have prevented many marine invertebrates from being able to form shells. Fossils of some of the ocean's most plentiful shelled organisms, tiny creatures called foraminifera, reveal that some combination of the low pH and greatly reduced oxygen levels led to the extinction of more than 50 percent of all deep-sea foraminifera species. On land, the warming trend made palm trees grow in present-day Wyoming and Montana and the ancestors of today's crocodiles migrate as far north as Canada. There is evidence that the Arctic Ocean had no ice during this time and that the first primates and horses took advantage of the warmth to expand from their place of origin in central Asia to other continents on their way to replacing the position of dominance ceded by dinosaurs 10 million years earlier. All this from one 1,000-year burp. (VIDEO: Richard Norris describes the changed world of the Paleocene-Eocene Thermal Maximum)  Geologist Lisa Tauxe demonstrates the use of a Brunton to students J.J. Becker and Ritayan Mitra Scripps geologist Richard Norris, the principal investigator on the Cedar Breaks trip, considers two other components of the PETM climate. One is that, cataclysmic as it was, the PETM might not have unfolded rapidly enough to serve as an adequate analogy to what's happening today. The second is that once the atmosphere was loaded with CO2, it may have taken as much as 200,000 years for the skies and oceans and all the organisms within them to return to their pre-PETM states. "If we can figure out how rapid the input was, then we can make a much better assessment of the extent to which this is comparable to modern times," he said. The hiking area around to the northwest of the Cedar Breaks ranger station and visitors center is called Twisted Forest for its wind-sculpted trees. Somebody in the research group called it "Twisted Sister" as a joke and the name stuck. After a day of scouting, Norris and Lisa Tauxe, a Scripps researcher and expert in paleomagnetism, decided that Twisted Sister bears what Norris calls the best "low-hanging fruit," accessible samples of 55-million-year-old rock. |
Multimedia
Related LinksShare This Story
"If we can figure out how rapid the input was, then we can make a much better
assessment of the extent to which this is comparable to modern times"
|
|
