Posted: 22 Mar 2010 01:23 PM PDT
Geologists have turned a series of 200 million-year-old lake-bed sediments into an epic narrative of the dinosaurs' journey from ecological obscurity to Earthly supremacy, a mystery that has lingered even as their disappearance is explained.
The dino path to dominance appears to have been cleared when the supercontinent Pangea cracked, setting off 600,000 years of volcanic activity that wiped out the dinosaurs' crocodilian competitors.
"This is the strongest case for a volcanic cause of a mass extinction event to date," wrote geoscientists in a paper published March 22 in the Proceedings of the National Academy of Sciences.
From 250 million to 200 million years ago, dinosaurs were just upstart lizards. The planet was dominated by a family of vaguely crocodile-like animals called crurotarsans that filled every major ecological niche, from slow-munching herbivores to fleet predators.
About halfway through that period, known as the Triassic, an asteroid struck Earth. Many of the planet's species went extinct, but the crurotarsans weathered the storm. Then, 25 million years after that, in what's known as the Triassic-Jurassic extinction event, the crurotarsans and at least half of all other animal species vanished. Exactly why isn't known, but scientists now have a pretty good idea.
Geological records show that Pangea, the giant land mass that once contained the seven modern continents, broke up about 200 million years ago. The North American plate and the African plate drifted apart, leaving a fissured basin that eventually became the Atlantic Ocean. Magma spurted through the cracks, forming a 3.5 million-square-mile lake of lava called the Central Atlantic magmatic province (marked in pink on the map below).
In a paper published in 2007, Brown University geologist Jessica Whitesides, co-author of the new study, showed that the Atlantic basin stayed volcanic for 610,000 years, plenty long enough to shroud the planet in greenhouse gases. The new study backs up that explanation.
The researchers analyzed sediment layers at sites in New Jersey, Connecticut and England, where lakes had been swallowed by lava at different times after the break up of Pangea. The sediments contained fossil pollen. Each grain had a telltale carbon atom signature, allowing them to put the samples in chronological order. Pollen records were then cross-referenced with footprints left in the lake beds by dinosaurs and crurotarsans.
A clear picture emerged. As the volcanism continued, floral species vanished. By the end of the volcanic period, half were gone. So were almost all crurotarsans. As their footprints vanished, those of the dinosaurs grew larger and more frequent. They were taking over.
For the next 135 million years, the great lizards ruled Earth. Then an asteroid struck the Yucatan Peninsula. Just as the crurotarsans had given way to the dinosaurs, the dinosaurs gave way to the latest upstart animal: a class of hairy, warm-blooded creatures called mammals.
Images: 1) Clockwise from left, three crurotarsans: Saurosuchus galilei, Pedeticosaurus leviseuri and Dakosaurus maximus/Wikipedia. 2) Map of Pangea as it appeared 201 million years ago; the red field is the Central Atlantic magmatic province, and red dots indicate sites discussed in the paper/PNAS.
Citation: "Compound-specific carbon isotopes from Earth's largest flood basalt province directly link eruptions to the end-Triassic mass extinction," by Jessica Whiteside, Paul Olsen, Timothy I. Eglinton, Michael Brookfield, and Raymond Sambrotto. Proceedings of the National Academy of Sciences, Online Early Edition, March 22, 2010.
Posted: 22 Mar 2010 09:50 AM PDT
SAN FRANCISCO — Roasting coffee beans doesn't just impart bold, rich flavor. It also creates a compound that helps dial down production of stomach acid, according to research presented on March 21 at the spring meeting of the American Chemical Society. The discovery may explain why dark-roasted brews are gentler on the stomach than their lighter peers, and could lead to a new generation of tummy-friendly coffees.
Even though several studies have found a cup-a-day habit imparts health benefits such as decreased risk of obesity, Alzheimer's and colon cancer, many coffee lovers drink decaf or forgo the beverage altogether because it irritates the stomach or spurs heartburn. Previous work suggested that coffee made from steam-treated beans tamps down this gastric distress, a finding attributed to lower levels of caffeine and other compounds in these brews.
"But there is no experimental or human data that says these compounds increase gastric acid," said Veronika Somoza of the University of Vienna, who presented the research.
To explore the science behind these gentler brews, Somoza and her colleagues used water and three other solvents to extract compounds from regular commercial coffee blends. Each solvent extracted a different profile of compounds, including caffeine and N-methylpyridinium, a ringed compound that doesn't appear in green coffee beans but is created in the roasting process. Stomach cells exposed to each suite of compounds upped their acid secretion, except for the cells exposed to the extract containing NMP.
The team then compared the chemical profiles of a dark-roasted and light-roasted brew made with regular roasted and steam-treated beans. Both versions of the dark-roasted coffee had more than 30 milligrams per liter of NMP, as compared with the lighter roast, which had 22 mg/l. The light roast that was subjected to steam treatment, a technique thought to weaken coffee's stomach-provoking powers, had a mere 5 mg/l of NMP.
Follow-up work confirmed the molecule's mild-mannered nature. Human stomach cells treated with coffee that had medium or high concentrations of NMP secreted far less acid than cells treated with coffee containing the least amount of NMP, Somoza reported. And the activity of many of the genes and proteins involved in this gastric secretion were quashed in cells exposed to NMP-rich coffee.
The research team is now conducting a pilot study in which subjects swallow a sensor embedded in a capsule that measures the stomach's pH and transmits the readings to a computer. Preliminary results suggest that stomach acid surges for a longer time when subjects drink light-roast coffee compared to dark-roast.
"Most people think that non-processed food is beneficial, that possibly raw foods are best, but we do not believe that," Somoza said. "There are healthy, beneficial compounds in processed food. Our idea is to identify these beneficial compounds and enhance them."
How NMP acts on the gastric system isn't well understood. Acid secretion didn't change noticeably in stomach cells treated with NMP alone. And caffeine's name hasn't been cleared — the friendlier darker brews also had less caffeine than their lighter-brewed counterparts.
This lower caffeine may also contribute to the darker roasts' antacid powers. While chemists are fond of breaking bigger things into their smaller parts, these parts often work in concert, said Bhimu Patil of Texas A&M University in College Station. "It's important to break things down to understand them, but most of the time, there is a synergistic effect."
Image: eclectic echoes/flickr
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