08. The Past 750 Myrs

High and Lows Over the Past 750 Million Years

2016-10-10. Simulating the Climate 145 Million Years Ago. By Shannon Hall, Earth and Space Science News (EoS, AGU).

2015-01-15. Tiny plant fossils offer window into Earth's landscape millions of years ago. NSF Press Release 15-003.

2014-02-20. Seeking a Break in a 252 Million-Year-Old Mass Killing. A Geologist Investigates a Mass Extinction at the End of the Permian Period.   Excerpt: Sam Bowring ... a geologist at M.I.T. ... wants to understand how an estimated 96 percent of all species on Earth became extinct at the end of the Permian Period 252 million years ago...the biggest of the five mass extinctions recorded in the fossil record. ...Dr. Bowring and his colleagues have ... made the most precise measurement yet of how long it took for all those species to become extinct...less than about 60,000 years. That’s a geological blink of an eye — a fact that will help scientists evaluate different hypotheses for what triggered the mass extinction. ...Studies on the rocks that formed around the time of the mass extinction ... revealed that ...Huge volcanoes in Siberia belched molten rock that covered millions of square miles. The oceans warmed dramatically, climbing 18 degrees Fahrenheit. ...the carbon in the rocks that formed around the time of the mass extinction...have a drastically higher ratio of light-to-heavy carbon. One way to create such a planet-wide shift would be to deliver a huge surge of carbon dioxide into the ocean. ...The volcanoes may well be the cause, but scientists have yet to establish all the links from eruptions to extinctions. ...the Siberian eruptions lasted for one to two million years. But the world’s biodiversity did not decline over a similar time scale. Instead, it swiftly collapsed with little advance warning.... http://www.nytimes.com/2014/02/21/science/earth/Mass-Extinction-Permian-Period.html. Carl Zimmer, The New York Times.

2013-10-08. When CO2 Levels Doubled 55 Million Years Ago, Earth May Have Warmed 9°F In 13 Years.  Excerpt: The Paleocene/Eocene thermal maximum (PETM) and associated carbon pulse “are often touted as the best geologic analog for the current” manmade rise in CO2 levels, as a new study notes. The Proceedings of the National Academy of Sciences paper, “Evidence for a rapid release of carbon at the Paleocene-Eocene thermal maximum,”  ...Rutgers geologists Morgan Schaller and James Wright argue that: … following a doubling in carbon dioxide levels, the surface of the ocean turned acidic over a period of weeks or months and global temperatures rose by 5 degrees centigrade – all in the space of about 13 years. Scientists previously thought this process happened over 10,000 years. ...Note that if we stay anywhere near our current emissions path, we are headed for a tripling or quadrupling of CO2 concentrations from preindustrial levels. ...the “dean of climate scientists,” Wallace Broecker who popularized the term “global warming” ...decades ago... said, “The climate system is an angry beast, and we are poking at it with sticks.” ...“My point [with the 'angry beast' metaphor] was that by adding large amounts of CO2 to the atmosphere, we were poking our climate system without being sure how it would respond,” he says. At the rate we are spewing carbon pollution into the atmosphere, one might even say we are punching the climate beast in the nose. Paleoclimate studies, including this new one, suggests that is a very, very bad move.... http://thinkprogress.org/climate/2013/10/08/2750191/petm-co2-levels-doubled-55-million-years-ago-global-temperatures-jumped/. Joe Romm, ThinkProgress.

2012-12-09. 5 million-year hangover | By  Spencer Hunt, The Columbus Dispatch. Excerpt:  Scientists say climate change slowed recovery after the world’s greatest extinction event 250 million years ago. …250 million years ago during a time that scientists call the Great Dying … world’s greatest extinction event wiped out 90 percent of life in the oceans and about 70 percent on land. Earth did recover, but it took about 5 million years, according to a team of earth scientists, including Ohio State University geologist Matthew Saltzman. “That’s a relatively long amount of time,” he said. “We see mass extinctions throughout Earth’s history and, in most cases, the recovery took place in about 1 million years or so.” …the mass extinction was triggered by a series of severe volcanic eruptions in a region called the Siberian Traps. After 1 million years of heavy volcanic activity, an area larger than Europe was covered in a layer of once-molten igneous rock 1 mile to 3 miles thick…. Researchers theorize that magma from the initial eruptions burned through an ancient coal bed. …Thomas Algeo, a University of Cincinnati geologist, said huge amounts of carbon dioxide and methane were released, killing off most remaining species.  …After the Great Dying, increases in global temperatures made life nearly impossible for plants and animals on land and heated the oceans to an average 100 degrees Fahrenheit. …Saltzman said the Great Dying offers a window on the effects of climate change. He and Algeo cautioned that the current predictions for climate change are far from the global catastrophe that occurred 250 million years ago. …the average temperature increase then was two to three times higher than the increase climatologists are forecasting. Still, Saltzman said reactions to climate change can be severe…. Read the full article: http://www.dispatch.com/content/stories/science/2012/12/09/5-million-year-hangover.html

2012-09-10. Earlier Mass Extinction for Most of Marine Life | by Sindya Bhanoo, New York Times.  Excerpt:  Most scientists agree that dinosaurs became extinct as a result of a catastrophic meteor strike 65 million years ago near the Yucatán Peninsula. …But now scientists are suggesting that another mass extinction event occurred about 200,000 years earlier: a volcanic eruption on the Deccan Plateau of India. The eruption filled the atmosphere with aerosols — fine particles suspended in greenhouse gases that led to warming and, eventually, the extinction of much of marine life, especially shelled invertebrates on the ocean floor….. Read the full article: http://www.nytimes.com/2012/09/11/science/volcanic-eruption-may-have-caused-marine-life-extinction.html?ref=science

2010 April 9.  Scientists Explore Origins of 'Supervolcanoes' on the Sea Floor. National Science Foundation Update. Excerpt: "Supervolcanoes" have been blamed for multiple mass extinctions in Earth's history, but the cause of their massive eruptions is unknown. ..."'Supervolcanoes' emitted large amounts of gases and particles into the atmosphere, and re-paved the ocean floor," says Rodey Batiza, marine geosciences section head in the National Science Foundation (NSF)'s Division of Ocean Sciences, which co-funded the research. The result? "Loss of species, increased greenhouse gases in the atmosphere, and changes in ocean circulation," says Batiza. In fall 2009, an international team of scientists participating in IODP Expedition 324 drilled five sites in the ocean floor. They studied the origin of the 145 million-year-old Shatsky Rise volcanic mountain chain... 1,500 kilometers (930 miles) east of Japan, ... roughly the size of California... one of the largest supervolcanoes in the world: the top of Shatsky Rise lies three and a half kilometers (about two miles) below the sea's surface, while its base plunges to nearly six kilometers (four miles) beneath the surface. ... composed of layers of hardened lava, with individual lava flows that are up to 23 meters (75 feet) thick.
...About a dozen supervolcanoes exist on Earth; some are on land, while others lie at the bottom of the ocean. Those found on the seafloor are often referred to as large oceanic plateaus. Current scientific thinking suggests that these supervolcanoes were caused by eruptions over a period of a few million years or less--a rapid pace in geologic time.
...Shatsky Rise ... is ... the only supervolcano to have formed during a time when Earth's magnetic field reversed frequently." This process creates "magnetic stripe" patterns in the seafloor. "We can use these magnetic stripes to decipher the timing of the eruption," says Sager"....

2010 March 4. NSF Release 10-037: Scientists Find Signs of "Snowball Earth" Amidst Early Animal Evolution. Excerpt: Geologists have found evidence that sea ice extended to the equator 716.5 million years ago, bringing new precision to a "snowball Earth" event long suspected to have taken place around that time.
...The new findings--based on an analysis of ancient tropical rocks that are now found in remote northwestern Canada--bolster the theory that our planet has, at times in the past, been ice-covered at all latitudes.
"This is the first time that the Sturtian glaciation has been shown to have occurred at tropical latitudes, providing direct evidence that this particular glaciation was a 'snowball Earth' event," says lead author Francis Macdonald, a geologist at Harvard University.
...According to Enriqueta Barrera, program director in NSF's Division of Earth Sciences, which supported the research, the Sturtian glaciation, along with the Marinoan glaciation right after it, are the greatest ice ages known to have taken place on Earth. "Ice may have covered the entire planet then," says Barrera, "turning it into a 'snowball Earth.'"
The survival of eukaryotes--life forms other than microbes such as bacteria--throughout this period suggests that sunlight and surface water remained available somewhere on Earth's surface. The earliest animals arose at roughly the same time.
..."The fossil record suggests that all of the major eukaryotic groups, with the possible exception of animals, existed before the Sturtian glaciation," Macdonald says. "The questions that arise from this are: If a snowball Earth existed, how did these eukaryotes survive? Did the Sturtian snowball Earth stimulate evolution and the origin of animals?"...

2009 June 21. Carbon Dioxide Higher Today Than Last 2.1 Million Years. ScienceDaily. Excerpt: Researchers have reconstructed atmospheric carbon dioxide levels over the past 2.1 million years in the sharpest detail yet, shedding new light on its role in the earth's cycles of cooling and warming.
The study...is the latest to rule out a drop in CO2 as the cause for earth's ice ages growing longer and more intense some 850,000 years ago. But it also confirms many researchers' suspicion that higher carbon dioxide levels coincided with warmer intervals during the study period.
The authors show that peak CO2 levels over the last 2.1 million years averaged only 280 parts per million; but today, CO2 is at 385 parts per million, or 38% higher. This finding means that researchers will need to look back further in time for an analog to modern day climate change.
In the study, Bärbel Hönisch, a geochemist at Lamont-Doherty Earth Observatory, and her colleagues reconstructed CO2 levels by analyzing the shells of single-celled plankton buried under the Atlantic Ocean, off the coast of Africa. By dating the shells and measuring their ratio of boron isotopes, they were able to estimate how much CO2 was in the air when the plankton were alive. This method allowed them to see further back than the precision records preserved in cores of polar ice, which go back only 800,000 years.
...The low carbon dioxide levels outlined by the study through the last 2.1 million years make modern day levels, caused by industrialization, seem even more anomalous, says Richard Alley, a glaciologist at Pennsylvania State University, who was not involved in the research.
"We know from looking at much older climate records that large and rapid increase in CO2 in the past, (about 55 million years ago) caused large extinction in bottom-dwelling ocean creatures, and dissolved a lot of shells as the ocean became acidic," he said. "We're heading in that direction now."...

14 November 2006. Paleoclimatology: Understanding the Past to Predict the Future. By Holli Riebeek. Scientists use complicated climate models to predict how Earth's climate might change in the future. One of the best ways to test the reliability of such models is to see how well they recreate climates of the past.

7 November 2006 In Ancient Fossils, Seeds of a New Debate on Warming. By WILLIAM J. BROAD. NY Times. Excerpt: In recent years, scientists have learned about the changing makeup of the vanished gases by teasing subtle clues from fossilized soils, plants and sea creatures. They have also gained information from computer models that predict how phenomena like eroding rocks and erupting volcanoes have altered the planet's evolving air. "It's getting a lot more attention," Michael C. MacCracken, chief scientist of the Climate Institute, a research group in Washington, said of the growing field. For the first time, the Intergovernmental Panel on Climate Change, a United Nations group that analyzes global warming, plans to include a chapter on the reconstructions in its latest report, due early next year.The discoveries have stirred a little-known dispute that, if resolved, could have major implications. One side foresees a looming crisis of planetary heating; the other, temperature increases that would be more nuisance than catastrophe. Some argue that CO2 fluctuations over the Phanerozoic follow climate trends fairly well, supporting a causal relationship between high gas levels and high temperatures. Other experts say that the fluctuations in the gas levels often fall out of step with the planet's hot and cold cycles, undermining the claimed supremacy of carbon dioxide. Highlighting the gap, the two sides clash on how much the Earth would warm today if carbon dioxide concentrations double from preindustrial levels, as scientists expect. Many climatologists see an increase of as much as 8 degrees Fahrenheit. Carbon dioxide skeptics and others see the reconstructions of the last 15 years as increasingly reliable, posing fundamental questions about the claimed powers of carbon dioxide. "Some of the work has been quite meticulous," Thure E. Cerling, an expert at the University of Utah on Phanerozoic climates, said. "We are likely to learn something."

27 December 2005. Past Hot Times Hold Few Reasons to Relax About New Warming. By ANDREW C. REVKIN. Excerpt: Earth scientists with the longest frames of reference...often seem to be the least agitated about human-caused global warming ... these backward-looking experts have seen it all before. ... 49 million years ago the balmy Arctic Ocean, instead of being covered in ice, was matted with a cousin of the duckweed that cloaks suburban frog ponds. The forests on the continent now called Antarctica and on shores fringing the Arctic were once thick and lush. And through hundreds of millions of years, concentrations of carbon dioxide and the other trace gases that trap solar energy and prevent the planet from being an ice ball have mostly been far higher than those typical during humankind's short existence. ... A hot, steamy earth would be fine for most forms of life. ...Studies of the past also show that pace matters. The rise in temperature and greenhouse gases during the great heat wave 55 million years ago, while instantaneous on a geological time scale, took thousands of years to unfold. But the pace of the recent rise in carbon dioxide is as much as 200 times as fast as what has been estimated in past rapid climate transitions.

May 2005. Weathering Climate Variability. ScienceMatters@Berkeley. When it comes to weather, most of us are only concerned with the forecast. UC Berkeley professor Lynn Ingram is more interested in old news. Very old. She studies how California's climate has changed over thousands of years. Her research could help prepare us for what tomorrow's weather may bring.

Historical Isotopic Temperature Record from the Vostok Ice Core

CLIMATE TIME LINE INFORMATION TOOL. The Climate Time Line Information Tool (CTL) is being developed and evaluated by science educators at the University of Colorado and NOAA as a tool for exploring the complex world of climate science and history. The developers ultimately see the prototype supporting science concepts such as systems, cycles, energy transfer, patterns and scale, and science as inquiry. The site's basic design is an interactive matrix that uses the "powers of ten" approach to frame 1) climatic processes and 2) specific climate events of the past at varying time scales. Each time scale has its own list of sources and links to more information. The web site is a work in progress and the developers would like feedback from science educators and students. Audience: college level instruction.


Archive of Past Articles for Chapter 8