09. Dinosaurs

What Happened to the Dinosaurs?

2015-10-01. Volcano-asteroid combo may have done in the dinosaurs. By Sid Perkins, Science.

2013-03-27.  New Evidence Ancient Asteroid Caused Global Firestorm On Earth.   Excerpt: A new look at conditions after a Manhattan-sized asteroid slammed into a region of Mexico in the dinosaur days indicates the event could have triggered a global firestorm that would have burned every twig, bush and tree on Earth and led to the extinction of 80 percent of all Earth's species, says a new University of Colorado Boulder study. ...the collision would have vaporized huge amounts of rock that were then blown high above Earth's atmosphere. The re-entering ejected material would have heated the upper atmosphere enough to glow red for several hours at roughly 2,700 degrees Fahrenheit -- about the temperature of an oven broiler element -- killing every living thing not sheltered underground or underwater. ...there was enough infrared radiation from the upper atmosphere that reached Earth's surface to create searing conditions that likely ignited tinder, including dead leaves and pine needles. If a person was on Earth back then, it would have been like sitting in a broiler oven for two or three hours.... ...The asteroid-Earth collision is thought to have generated about 100 million megatons of energy.... http://www.sciencedaily.com/releases/2013/03/130327144249.htm. Science News.

2013-02-07.  New evidence comet or asteroid impact was last straw for dinosaurs | Robert Sanders, UC Berkeley News Center. Excerpt: The demise of the dinosaurs is the world’s ultimate whodunit. Was it a comet or asteroid impact? Volcanic eruptions? Climate change? ...In an attempt to resolve the issue, scientists at the Berkeley Geochronology Center (BGC), the University of California, Berkeley, and universities in the Netherlands and the United Kingdom have now determined the most precise dates yet for the dinosaur extinction 66 million years ago and for the well-known impact that occurred around the same time. The dates are so close, the researchers say, that they now believe the comet or asteroid, if not wholly responsible for the global extinction, at least dealt the dinosaurs their death blow. “The impact was clearly the final straw that pushed Earth past the tipping point,” said Paul Renne, BGC director and UC Berkeley professor in residence of earth and planetary science. “We have shown that these events are synchronous to within a gnat’s eyebrow, and therefore the impact clearly played a major role in extinctions, but it probably wasn’t just the impact.” The revised dates clear up lingering confusion over whether the impact actually occurred before or after the extinction, which was characterized by the almost overnight disappearance from the fossil record of land-based dinosaurs and many ocean creatures. The new date for the impact – 66,038,000 years ago – is the same within error limits as the date of the extinction, said Renne, making the events simultaneous. He and his colleagues will report their findings in the Feb. 8 issue of the journal Science…. Read the full article: http://newscenter.berkeley.edu/2013/02/07/new-evidence-comet-or-asteroid-impact-was-last-straw-for-dinosaurs/

2012 May 27. It Took Earth Ten Million Years to Recover from Greatest Mass Extinction | ScienceDaily. Excerpt: Life was nearly wiped out 250 million years ago, with only 10 per cent of plants and animals surviving…recovery from the crisis lasted some 10 million years…There were apparently two reasons for the delay, the sheer intensity of the crisis, and continuing grim conditions on Earth after the first wave of extinction.The end-Permian crisis, by far the most dramatic biological crisis to affect life on Earth, was triggered by a number of physical environmental shocks -- global warming, acid rain, ocean acidification and ocean anoxia. These were enough to kill off 90 per cent of living things on land and in the sea…Current research shows that the grim conditions continued in bursts for some five to six million years after the initial crisis, with repeated carbon and oxygen crises, warming and other ill effects.Some groups of animals on the sea and land did recover quickly and began to rebuild their ecosystems, but they suffered further setbacks. Life had not really recovered in these early phases because permanent ecosystems were not established….

2012-06-25. ‘Nature’s Masons’ Do Double Duty as Storytellers.  By Sean B. Carroll, New York Times. An article relevant to GSS Climate Change chapter 8, Life and Climate chapter 9, and A Changing Cosmos chapter 1. Excerpt: GUBBIO, Italy — …Limestone is composed largely of crystallized calcium carbonate. Some of it comes from the skeletal remains of well-known creatures like corals, but much of the rest comes from less appreciated but truly remarkable organisms called foraminifera, or forams for short. Forams have been called “nature’s masons,” … these single-celled protists construct surprisingly complex, ornate and beautiful shells to protect their bodies. After forams die, their shells settle in ocean sediments…. While tiny relative to ourselves …, forams are extremely large for single-celled organisms, … largest forams can reach a few centimeters. … forams are particularly valuable to geologists and paleontologists in telling us about Earth’s history. The forams in the limestone just outside Gubbio provided the first clues to … an asteroid that struck earth at the end of the Cretaceous period, 65 million years ago…about the size of Mount Everest and traveling at about 50,000 miles an hour when it hit the earth, drilling a 120-mile-wide crater and ejecting so much material into (and even out of) the atmosphere that food chains on land and in the oceans were disrupted for thousands of years. The impact caused one of the greatest mass extinctions in history, from the largest animals to tiny forams. Read the full article: http://www.nytimes.com/2012/06/26/science/natures-masons-do-double-duty-as-earths-storytellers.html?_r=1&emc=eta1

2012-04-05. Bus-Size Dinosaurs, Fuzzy as Chicks | by John Noble Wilford, The New York Times. An article relevant to GSS Life and Climate chapter 9. Excerpt: Fossils discovered in northeastern China of a giant, previously unrecognized dinosaur show that it is the largest known feathered animal, living or extinct, scientists report. …The adult was at least 30 feet long and weighed a ton and a half, …. The two juveniles were a mere half ton each. The new species was a distant relative of Tyrannosaurus rex …. Xing Xu of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, who was the lead author of the paper, said …that it was “possible that feathers were much more widespread, at least among meat-eating dinosaurs, than most scientists would have guessed even a few years ago.” Dr. Xu said the feathers were simple filaments, more like the fuzzy down of a modern baby chick than the stiff plumes of an adult bird. Such insubstantial feathers, not to mention the animal’s huge size, would have made flight impossible. The feathers’ most important function was probably as insulation. The species has been named Yutyrannus huali, which means “beautiful feathered tyrant” in a combination of Latin and Mandarin. Mark A. Norell, a curator of paleontology at the American Museum of Natural History in Manhattan, who had no part in the research, said the findings were significant because they swept aside a longstanding argument that perhaps dinosaurs had feathers only when they were small and shed them as they grew…. Read the full article: http://www.nytimes.com/2012/04/05/science/dinosaur-dig-in-china-turns-up-largest-known-feathered-animal.html?_r=1&nl=todaysheadlines&emc=edit_th_20120405

2012 Feb 3. Global Extinction: Gradual Doom as Bad as Abrupt. NSF Press Release 12-019. Excerpt: The deadliest mass extinction of all took a long time to kill 90 percent of Earth's marine life--and it killed in stages--according to a newly published report. It shows that mass extinctions need not be sudden events. Thomas Algeo, a geologist at the University of Cincinnati, and 13 colleagues have produced a high-resolution look at the geology of a Permian-Triassic boundary section on Ellesmere Island in the Canadian Arctic.

2010 May 17. Ancient mass extinction of fish may have paved way for modern species. By Amina Khan, LA Times. Excerpt: ..."It's clearly one of the most important papers published in recent years" in paleontology, said John Long, a paleontologist at the Natural History Museum of Los Angeles County who was not involved in the study. "Forty-four percent of all vertebrate life went extinct at that point, and that was not recognized before."

...That event was one of the most devastating in Earth's history, on a par with the one that killed off the dinosaurs 65 million years ago, said Lauren Sallan, a paleontologist at the University of Chicago and lead author of the paper.

...And just as the fall of the dinosaurs made room for mammals to rise, she said, this extinction made way for modern marine life such as sharks and the ancestors of modern fish — as well as for tetrapods, ancestors of terrestrial vertebrate life.

2010 March 23. Dinosaurs' dominance 'helped by mass volcanism'. By Paul Rincon, BBC News. Excerpt: Immense volcanic activity helped the dinosaurs rise to prominence some 200 million years ago, a study suggests.
Dinosaurs were the dominant vertebrates on land for some 135 million years.
While it is widely accepted that an asteroid or comet wiped them out, there has been less agreement on the factors which led to their ascendancy.
Research in PNAS journal suggests volcanic eruptions changed the climate, causing a mass extinction that wiped out the dinosaurs' main competitors.
The scientific paper...looked at several lines of evidence such as the remains of plant wax and wood from sedimentary rocks interbedded with lava flows. From these, they were able to extract vital data about the climate at this time.
The lava flows are dated to the end-Triassic extinction, 201.4 million years ago, which wiped out 50% of tetrapods (four-limbed animals) on land, 50% of terrestrial plants and 20% of marine families....

2010 March 9. Alvarez Theory on Dinosaur Die-Out Upheld: Experts Find Asteroid Guilty of Killing the Dinosaurs. By Lynn Yarris, Lawrence Berkeley National Laboratory. Excerpt: In the March 5, 2010 edition of the journal Science, an international panel of 41 experts in geology, paleontology and other related fields, after an exhaustive review of the data, declared an end to a 30 year controversy over what triggered the extinction of the dinosaurs – an asteroid or volcanoes. The panel ruled in favor of the asteroid, a theory first put forth in 1980 by one of Berkeley Lab’s greatest scientists, the late Nobel laureate Luis Alvarez, and his son Walter, a geologist with UC Berkeley....

2009 April 28. New Blow Against Dinosaur-killing Asteroid Theory, Geologists Find. ScienceDaily. Excerpt: The enduringly popular theory that the Chicxulub crater holds the clue to the demise of the dinosaurs, along with some 65 percent of all species 65 million years ago, is challenged in a paper to be published in the Journal of the Geological Society on April 27, 2009.
The crater, discovered in 1978 in northern Yucutan and measuring about 180 kilometers (112 miles) in diameter, records a massive extra-terrestrial impact.
When spherules from the impact were found just below the Cretaceous-Tertiary (K-T) boundary, it was quickly identified as the "smoking gun" responsible for the mass extinction event that took place 65 million years ago.
It was this event which saw the demise of dinosaurs, along with countless other plant and animal species.
However, a number of scientists have since disagreed with this interpretation.
The newest research, led by Gerta Keller of Princeton University in New Jersey, and Thierry Adatte of the University of Lausanne, Switzerland, uses evidence from Mexico to suggest that the Chicxulub impact predates the K-T boundary by as much as 300,000 years.
...From El Penon and other localities in Mexico, says Keller, "we know that between four and nine meters of sediments were deposited at about two to three centimeters per thousand years after the impact. The mass extinction level can be seen in the sediments above this interval."
...The scientists also found evidence that the Chicxulub impact didn't have the dramatic impact on species diversity that has been suggested.
..."We found that not a single species went extinct as a result of the Chicxulub impact," says Keller.
...Keller suggests that the massive volcanic eruptions at the Deccan Traps in India may be responsible for the extinction, releasing huge amounts of dust and gases that could have blocked out sunlight and brought about a significant greenhouse effect....

2008 December 15. Fight over dinosaur death flares anew in S.F. By David Perlman, San Francisco Chronicle. Excerpt: SAN FRANCISCO -- The age of the dinosaurs ended abruptly about 65 million years ago when some catastrophic event drove them to extinction, and now a vehement controversy over their disappearance is emerging anew.
...An international group of scientists is arguing that poisonous fumes from violent waves of volcanic eruptions in India millions of years ago killed off the beasts, not - as UC Berkeley scientists first proposed nearly 30 years ago - the impact of a giant meteorite that blasted a huge undersea crater in Mexico and touched off a kind of "nuclear winter" that darkened the skies with a pall of dust and debris that the creatures could not possibly have survived.
The origins of the big debate began nearly 30 years ago when the geologist Walter Alvarez at UC Berkeley and his father, Luis, a Nobel physics laureate, proposed that a cosmic collision by an object from space at least six miles wide crashed just off Mexico's Yucatan peninsula about 65 million years ago and created what is known as the Chicxulub crater.
...Gerta Keller of Princeton University..., joined by Vincent Courtillot of the University of Paris and Sunil Bajpai, of the Indian Institute of Technology, ...insisted that the impact crater was formed at least 300,000 years before the great extinction and "caused no species extinctions" - certainly not to the dinosaurs. She came to her conclusion, in part, by age-dating clusters of mineral spherules that presumably spewed out of the Chicxulub crater and landed in Texas, where Keller said she gathered and tested them.
Instead, she argued, the extinction coincided with three or four waves of volcanism in a region of northwest India known as the Deccan traps....
...Walter Alvarez...rejected the idea that volcanism in India was the sole cause of the mass extinction.
..."Few experts on the mass extinction would agree with Keller that the Chicxulub impact is older than the mass extinction," he said....

2008 Mar 25. Theory on Dinosaurs and Volcanic Activity 65 Million Years Ago. By HENRY FOUNTAIN, NY Times. Excerpt: An asteroid or comet impact gets most of the credit for the event that wiped out the dinosaurs 65 million years ago. But massive volcanic activity around the same time might have played a role, too, by pumping enormous amounts of gases containing sulfur and chlorine into the atmosphere. An analysis by Stephen Self of the Open University in Milton Keynes, England, and colleagues lends new support to that idea. By looking at tiny bits of glass that formed inside the lava flows, they've been able to reconstruct how much sulfur and chlorine were released. The volcanic activity over thousands of years produced a flood of lava, now known as the Deccan Trapps, that is thousands of feet thick over thousands of square miles of central India. The researchers' analysis, reported in Science, suggests the eruption could have produced ...on an annual basis, ...the amount of SO2 ... at least 10 times greater than the current amount released by worldwide volcanic activity. The environmental impact of that much gas, they add, was probably severe.

2007 November 6. Rethinking What Caused the Last Mass Extinction. By JOHN NOBLE WILFORD. NY Times. Excerpt: FREEHOLD, N.J. - Splashing through a shallow creek in suburban New Jersey, the paleontologists stepped back 65 million years to the time of the last mass extinction, the one notable for the demise of the dinosaurs. ...At the time, sea levels were higher and New Jersey was warmer. The proto-Atlantic waters reached the center of the current boundaries of New Jersey, standing more than 60 feet deep here, where on a recent day the paleontologists were up to their ankles in a creek. They had their eyes on the sediments in the bank just above the iridium clay. They call this the Pinna layer.
On previous visits, they had found in the Pinna rock and soil a surprising number of marine fossils, including small clams, crabs and sea urchins. There was an abundance of ammonites, considered index organisms of the uppermost Cretaceous environment. Somehow, here at least, life appeared to have not only persisted but also flourished for tens, perhaps hundreds, of years after the putative asteroid impact.
..."It is undeniable that the iridium spike at the base of the Pinna layer was produced by the impact," Dr. Landman said. "That's amazing and makes it hard to explain the ammonite abundances we find above the iridium anomaly."
Gerta Keller, a paleontologist and professor of geosciences at Princeton University, said the research by Dr. Landman's group "shows the complexity of this extinction event and the difficulty explaining it by the currently popular impact theory."....

28 November 2006. New York Times. Marine Life Leaped From Simple to Complex After Greatest Mass Extinction. By Andrew C. Revkin. Excerpt: At least five mass extinctions, most presumably caused by asteroids that struck the earth, have transformed global ecology in the half-billion years since the emergence of multicelled life, lopping entire branches from the evolutionary tree and causing others to flourish. The greatest "great dying," 251 million years ago, erased 95 percent of species in the oceans (and most vertebrates on land). But new research suggests that it was followed by an explosion of complexity in marine life, one that has persisted ever since. Moreover, it happened quite suddenly... The shift to complicated, interrelated ecosystems was more like a flip of a switch than a slow trend. The researchers detected the change by analyzing records of marine fossils from 1,176 sites around the world, which are part of a new international archive, the Paleobiology Database (pbdb.org).

23 September 2006. DINOSAURS' CLIMATE SHIFTED TOO, REPORT SHOWS. Ancient rocks suggest dramatic climate changes during the dinosaur-dominated Mesozoic Era, a time once thought to have been hot and humid. NASA Earth Observatory.

20 September 2005. Fossils Offer Support for Meteor's Role in Dinosaur Extinction. By WILLIAM J. BROAD. For more than a decade, the standard view has envisioned a speeding object from space that crashed into the earth and kicked up enough dust and rock around the globe to blot out the sun. The smoking gun seemed to be the discovery beneath the Yucatán peninsula of Mexico of a 110-mile-wide crater called Chicxulub, after a nearby town. But lately, doubters have argued that Chicxulub formed 300s,000 years before the mass extinction - too early to have played a role in the demise of the dinosaurs and hundreds of other plant and animal species that vanished at the end of the Cretaceous. ...Now, in the September issue of Geology, the scientists, from Spain, Cuba and Mexico, report that they have discovered a highly disturbed bed of fossils that bears numerous signatures of Chicxulub's mayhem. The date of the disturbance, 65 million years ago, is exactly at the end of the Cretaceous. ...Starting around 2000, Dr. Alegret and her European colleagues repeatedly sought work permits for a nearby hill but always met with stultifying delays, if not outright rejections. Finally, they slipped into the site with their Cuban colleagues, going in late 2000, 2002 and 2003. ...A rocky outcrop on the hill showed an exposed bed of sedimentary rock made up of broken bits of minerals and fossils. It was more than 30 feet thick. The team took 66 samples. Examination with microscopes showed numerous signs of cosmic violence, including quartz deformed by high temperatures and pressures, as well as tiny spheres of glass, both clearly debris from a spectacular fireball. Microscopic study also revealed the presence of thousands of tiny fossil creatures, most especially foraminifera. ... Forams, as they are known, evolve so fast that geologists, paleontologists and oil companies use their shifting appearance as reliable guides to geologic dating. "They told the age of the sediments," Dr. Alegret said. "So we've definitely confirmed the age of these deposits." At the end of the Cretaceous, the rocky bed now in Cuba formed on the ocean bottom at a depth of perhaps 3,300 feet, over a few days or weeks as tons of debris rained down from the sky and huge waves generated by the Chicxulub event washed land out to sea. "It was geologically instantaneous," Dr. Alegret said of the deposit's formation.

10 March 2005. Mass extinction comes every 62 million years, UC physicists discover. David Perlman, SF Chronicle Science Editor. Excerpt: With surprising and mysterious regularity, life on Earth has flourished and vanished in cycles of mass extinction every 62 million years, say two UC Berkeley scientists who discovered the pattern after a painstaking computer study of fossil records going back for more than 500 million years. Their findings are certain to generate a renewed burst of speculation among scientists who study the history and evolution of life. Each period of abundant life and each mass extinction has itself covered at least a few million years -- and the trend of biodiversity has been rising steadily ever since the last mass extinction, when dinosaurs and millions of other life forms went extinct about 65 million years ago....Richard Muller and his graduate student, Robert Rohde, are publishing a report on their exhaustive study in the journal Nature today, and in interviews this week, the two men said they have been working on the surprising evidence for about four years. "We've tried everything we can think of to find an explanation for these weird cycles of biodiversity and extinction," Muller said, "and so far, we've failed." But the cycles are so clear that the evidence "simply jumps out of the data," said James Kirchner, a professor of earth and planetary sciences on the Berkeley campus who was not involved in the research but who has written a commentary on the report that is also appearing in Nature today..

26 December 2004. About tsunami from asteroidal impacts: Deep-sea waves generated at contact by asteroids varying in diameter from 1-100km (unaffected by interaction with sea floor) could reach heights of about 1 km, according asteroidal impact modeling studies (e.g. Gisler, Weaver, et al. 2002). This would translate into multi-km wave heights upon arrival in shallow/shore waters. Thankfully, these are rather rare events, even by geological standards.

26 August 2004. Ground Zero for the "Great Dying"? - J. KELLY BEATTY, Sky & Telescope magazine. Excerpt: IT'S BEEN NEARLY a quarter century since geologists realized that a colossal impact contributed to (and probably caused) the demise of the dinosaurs and most of Earth's other species 65 million years ago. ...In the years since, researchers have sought evidence linking impacts with other mass extinctions throughout geologic history. The worst of these die-offs brought an abrupt end to the vibrant Permian period 251 million years ago, nearly sterilizing Earth by wiping out 90 percent of all marine species and 70 percent of those on land in less than 160,000 years. No compelling explanation for the Permian-Triassic extinction - widely called the "Great Dying" - has yet gained favor. But recent research suggests that, coincidence or not, the Great Dying was accompanied by a Great Wallop. Fallout from a major blast has been found at the Permian-Triassic boundary in Antarctica, Australia, China, and Japan (S&T: June 2001, page 26). Now seven geoscientists, led by Luaim Becker (University of California, Santa Barbara), think they've found "ground zero" on the northwest margin of Australia. In the online journal ScienceExpress for May 13th, they argue that the Bedout High, a broad, lava-covered dome that today lies deeply buried beneath sea-floor sediment, is actually the uplifted center of a crater comparable in size to the huge Yucatan scar....But some impact specialists are skeptical For example, Andrew Glikson (Australian National University) found no evidence for impact-induced shock when he examined one of the Bedout drill cores. And none of the Permian-Triassic boundary layers show a pronounced excess of iridium, a telltale trace element that's rare in Earth's crust but common in meteorites. Meanwhile, debate continues over whether the Permian-Triassic extinction was instead caused by a massive outflow of lava in what is now Siberia. All told, volcanoes disgorged some 2 million cubic kilometers of molten rock and inundated an area the size of Europe. That eruption, proponents argue, set off an abrupt green house effect or other climatic upheaval.

14 May 2004. Did an Impact Trigger the "Great Dying"? By J. Kelly Beatty, Sky & Telescope magazine. It's been nearly a quarter century since geologists realized that a colossal impact contributed to (and probably caused) the decimation of the dinosaurs and vast numbers of Earth's other species 65 million years ago. Eventually this event's smoking gun, a crater some 180 kilometers across, was discovered beneath what is now Mexico's Yucatán Peninsula. In the years since researchers have sought evidence linking impacts with other mass extinctions of life throughout geologic history. The biggest of these, 251 million years ago, ended the vibrant Permian period and nearly left Earth sterile: 90 to 95 percent of all species died within a geologic blink of an eye. No compelling explanation for the Permian-Triassic extinction - widely called the "Great Dying" - has yet gained favor. Now seven geoscientists, led by Luann Becker (University of California, Santa Barbara), believe they've identified evidence of a huge impact on the northwest margin of Australia. In the May 13th ScienceExpress, they claim that the Bedout High, a broad plateau now deeply buried beneath seafloor sediment, is actually the uplifted center of an impact crater comparable in size to the Yucatán's huge scar.

13 May 2004 NASA RELEASE: 04-159 -- Evidence Of Meteor Impact Found Off Australian Coast. An impact crater believed to be associated with the " Great Dying," the largest extinction event in the history of life on Earth, appears to be buried off the coast of Australia.

24 February 2004. Scientists want to be ready to block asteroid from hitting Earth. GARDEN GROVE, California (AP) -- The asteroid believed to have wiped out dinosaurs 65 million years ago was rare but hardly unique, say scientists gathered to discuss ways of aggressively defending our planet from another such space rock, including by detonating nukes in space. Asteroids capable of inflicting damage on a global scale hit the Earth roughly every million years, and we shouldn't dawdle in developing a method of deflecting them, say the scientists attending a four-day planetary defense conference in suburban Orange County.


17 January 2003. Columbia University Research Finds Correlation Between Meteorite and Comet Impacts and an Increase in Volcanic Activity Development. 10 Major Episodes of Extraterrestrial Impacts Found to Correlate with 9 Major Episodes of Volcanism. Earth Institute at Columbia University; Mary Tobin; 845-365-8607

11 December 2002. New Scientist -- Earth's volcanism linked to meteorite impacts. Large meteorite impacts may not just throw up huge dust clouds but also punch right through the Earth's crust, triggering gigantic volcanic eruptions. The idea is controversial, but evidence is mounting that the Earth's geology has largely been driven by such events. This would also explain why our planet has so few impact crater remnants.

December 2002. Did a Comet Swarm Kill the Dinosaurs? by DAVID TYTELL, Sky & Telescope magazine, p. 24. IN 1991 A MODERN SCIENTIFIC "WHODUNIT" WAS SOLVED WHEN geologists identified a deeply buried, 180-kilometer-Wide crater in the Yucatan peninsula. Now known as Chicxulub, the scar resulted from the impact of a 10-km asteroid or comet nucleus 65 million years ago. Geologic evidence indicates that the impact triggered global tidal waves, worldwide firestorms, and massive earthquakes. It also left a worldwide layer of extraterrestrial dust. When Earth finally returned to normal, the dinosaurs and the majority of all then-living species had gone extinct, opening the way for mammals to diversify and dominate Earth. ...Now a new study suggests that Chicxulub may not have been an isolated event. Rather, the dinosaurs may have been the victims of a one-two punch.

  Archive of Past Articles for Chapter 9