Smithsonian Science » geology

Book Review: Planetary Tectonics examines otherworldly landforms

John Barrat — Mon, 05 Apr 2010 15:06:19 +0000

In recent decades, manned and unmanned spacecraft have taken hundreds of thousands of detailed photographs of the terrestrial planets in our solar system, the distant outer planets and various asteroids, comets and planetary satellites. Much of the geology that has emerged from the study of these photographs is spelled out in the new book Planetary Tectonics, edited by Thomas Watters, senior scientist at the Center for Earth and Planetary Studies at the Smithsonian’s National Air and Space Museum, and Richard Schultz, Professor of Geological Engineering and Geomechanics at the University of Nevada.

Image right: A moasic photo of part of the Moon’s southern Mare Serenitatis showing wrinkle ridges.

This new book is a primer on the many different surface features that exist on the planets in our solar system, the internal and external forces that created these features and what they reveal about the conditions on the planets where they are found. From the wrinkle ridges of the moon, to the surface grooves of an asteroid or the fracture belts of Venus, Planetary Tectonics is a studious look at the complex interplay of powerful forces that act upon planetary crusts and the mechanical properties of the crusts themselves.

The number and diversity of tectonic landforms in our solar system “is truly remarkable,” Watters and Schultz write in the preface of their book. Photographs of these structures have stimulated a range of scholarly investigations, “from the characterization and modeling of individual classes of tectonic landforms to the assessment of regional and global tectonic systems,” the scientists write. Planetary Tectonics is an overview of the major themes of this research as they relate to each planet and small body. The book contains methods for mapping and analyzing planetary tectonic features and is illustrated with many diagrams and spectacular images. Planetary Tectonics, which is extensively referenced, provides a springboard to other sources of information, and is an essential reference for researchers and students alike. Published by Cambridge University Press, additional information about this new volume can be accessed at the Web address: www.cambridge.org/catalogue/catalogue.asp?isbn=9780521765732

Smithsonian’s National Gem Collection acquires a yellow fluorite from Tanzania

John Barrat — Wed, 21 Oct 2009 17:52:20 +0000

The Smithsonian’s National Gem and Mineral Collection at the National Museum of Natural History has recently acquired a rare, intense yellow fluorite gem from Tanzania. “This is our first fluorite specimen from Tanzania,” Curator Jeff Post explains. “We acquired this specimen because it is a very nice quality fluorite with an attractive color and it is large enough to be exhibited. It’s a beautiful addition to our collection.”

Fluorite is well known and prized for its rich variety of colors, most commonly pale green, purple, yellow, orange, blue, pink and colorless. Most fluorite specimens have a single color but a significant percentage occur as a glassy, many-hued vein mineral. When a specimen is multi-colored, the colors are arranged in bands or zones. A specimen might have a clear outer zone allowing a cube of purple fluorite to be seen inside, or a single fluorite could have several different color zones.

Traditionally, fluorite is used as a flux in the manufacture of steel. It has also been used instead of glass in some high performance telescopes and camera lenses. Due to its relative softness it is not widely used by jewelers, but fluorite remains one of the most popular minerals for mineral collectors.

Widely occurring, gem quality specimens are found in Germany, Austria, Switzerland, Norway, Mexico, England, Canada, Kenya, Korea, Pakistan, China, Tanzania, and the United States. The intense yellow color and 40.01 carat size of the Smithsonian’s recently acquired fluorite specimen make it a rare and important addition to the Smithsonian’s National Gem and Mineral Collection. The stone is a gift of Dudley Blauwet, Blauwet Gems. —Jessica Porter

New Acquisition: With 1844 first edition, Smithsonian Libraries completes its collection of Charles Darwin’s three-volume geology series

John Barrat — Wed, 07 Oct 2009 11:22:10 +0000

Soon after Charles Darwin’s groundbreaking book On the Origin of Specieswas published in 1859, it found supporters among the staff of the Smithsonian Institution in Washington, D.C. Smithsonian Secretary Joseph Henry held the book in high regard. So did naturalist Spencer Baird, Henry’s right hand man and the second secretary of the Smithsonian, and Smithsonian naturalist George Brown Goode.

Image: 1840 portrait of Charles Darwin by George Richmond

As Darwin’s theories on evolution continue to guide scientific research at the Smithsonian today, it is fitting that Smithsonian Institution Libraries has recently acquired a rare first edition of Darwin’s Geological Observations on the Volcanic Islands, Visited During the Voyage of H.M.S. Beagle, published in London in 1844.

The volume completes the Smithsonian’s collection of Darwin’s three-volume series, Geology of the Voyage of the Beagle, which also includes the volumes: The structure and distribution of coral reefs (London, 1842) and Geological observation on South America (London, 1846). All three books are now on display in the National Museum of Natural History exhibit Darwin’s Legacy, which celebrates the 150th anniversary of the publication of On the Origin of Species (published Nov. 24, 1859).

In 1831, Darwin, a recent graduate of Cambridge University, embarked upon an adventure as an unpaid naturalist aboard the H.M.S. Beagle. The Beagle left Plymouth, England on Dec. 27, 1831, and after sailing around the world, returned to Falmouth, England on Oct. 2, 1836. The Beagle’s journey took Darwin to many places, including Tahiti, the Galapagos Islands, New Zealand and Australia. Darwin’s geological work aboard the Beagle brought him his first fame as a scientist. In Tahiti, he developed his theory of the formation of atolls. He proposed that these ring-shaped coral reefs form when the ocean floor gradually subsides beneath an island. The atoll remains after the island has disappeared below the surface of the water. Later investigations confirmed Darwin’s insights.

Photo: Darwin’s Geological Observations on the Volcanic Islands, Visited During the Voyage of H.M.S. Beagle, on exhibit in Darwin’s Legacy at the National Museum of Natural History.

Published nearly 15 years before On the Origin of Species, the book Geological Observations on the Volcanic Islands, Visited During the Voyage of H.M.S. Beagle, “is an important text in the development of modern geology and in the evolution of Darwin’s thinking on the formation of the earth and the distribution of species,” explains Leslie Overstreet, curator of natural-history rare books at the Smithsonian Institution Libraries. “SIL’s primary mission is to support the Institution’s scientists and historians,” Overstreet explains. “Global volcanism is a major focus of study at the National Museum of Natural History, and our holdings of published works form a deep, rich resource for researchers.” —Jessica Porter

Bombarded with ultraviolet light, the blue Hope diamond glows red

John Barrat — Wed, 19 Aug 2009 12:17:53 +0000

Some research is best done behind heavy, locked doors.

When geologist Jeffrey Post recently embarked on an experiment involving the Hope Diamond, at 45.52 carats, the world’s largest deep-blue diamond and one of the most famous and valuable museum objects on earth, he and his colleagues locked themselves and the diamond inside a large vault in the depths of the Smithsonian’s National Museum of Natural History.

Photo: The 45.52 carat, deep-blue Hope Diamond is shown here inside its surrounding pendant of 16 pear- and cushion-cut white diamonds. (Photo by Chip Clark)

Post was investigating a phenomenon that the millions of museum visitors who gaze at the diamond on its rotating pedestal behind bulletproof glass will never see—the mysterious red phosphorescent glow the stone emits when exposed to ultraviolet light.

The Hope Diamond’s red glow has long been considered a unique property of that stone. Most blue diamonds produce a bluish-white phosphorescence if exposed to ultraviolet light. The few other diamonds known to emit red phosphorescence were commonly assumed to have been from the even larger original stone from which the Hope was cut.

“It is something that always intrigued people,” says Post, curator of the Smithsonian’s National Gem and Mineral Collection. “For people who like the whole idea of a curse and that kind of story, the fact that this thing phosphoresces a bloody red color is just too good to be true.”

Photo: The Hope Diamond, right, without its white-diamond pendant, and the 30.62 carat Blue Hart Diamond.

Post timed his research to occur in the hours after the museum closed for the evening and before it reopened the next day. With guards standing by, the diamond was removed from its pedestal in the Harry Winston Gallery.

“We had a local jeweler come in and take it out of its setting for us,” Post says. (The jeweler returned early the following morning to reset the stone.) Next, Post and fellow diamond investigators from the U.S. Naval Research Laboratory, Ocean Optics Co. and Pennsylvania State University locked themselves in the vault with the diamond and a portable spectrometer.

“The clock was running,” Post says, and the scientists got to work. The diamond was positioned on a piece of clay inside a box that could be sealed to keep out ambient light. A fiber-optic cable connected to an ultraviolet light source was extended into the box and “pushed up against the top face of the Hope Diamond,” Post says. Then the diamond was exposed to ultraviolet light for several seconds.

When the light source was turned off, the diamond began to emit its characteristic red glow, a phenomenon that lasts several minutes. A second fiber-optic cable in the box channeled phosphorescent light from the diamond to the spectrometer.

Photo: The Hope Diamond emits a red phosphorescence after being bombarded with ultraviolet light. (Photo by John Nels Hatleberg)

Spectrometers measure wavelengths of light, and the display on a laptop computer hooked to the spectrometer revealed the Hope Diamond’s red light was more than just red. “That was the first time we had been able to see a display of what the phosphorescence spectrum looked like for the Hope Diamond,” Post says.

“We saw two strong peaks in the spectrum,” Post explains. One was in the red portion of the spectrum, “but the second peak, interestingly, was in the green portion of the spectrum.”

In the vault that night, the scientists also collected spectrum readings from other diamonds, including the second largest known deep-blue diamond, the 30.62 carat Blue Heart, also in the Smithsonian’s gem collection.

Later, Post and his colleagues hauled their portable spectrometer to New York City’s Diamond District, an area of Manhattan that is a center of the world diamond industry. A dealer known to Post granted the researchers access to dozens of valuable blue diamonds in his safe for further spectrum measurements.

The scientists learned that all blue diamonds show red and green peaks in their phosphorescence spectrum. But the relative intensity of those peaks and the rate at which they decay varies from diamond to diamond, leading to differences in the phosphorescent glow seen by the naked eye.

Diamonds are composed of carbon, and impurities in the carbon give rise to an individual stone’s color. Blue diamonds have relatively high levels of boron impurities but low levels of nitrogen. Post believes that the red phosphorescence emitted to some degree by all blue diamonds is likely due to interaction between those two elements. To test that possibility, he is continuing his study of blue diamonds, using a different kind of instrument that lets him measure the amount of boron and nitrogen in individual stones “and then correlate that with the particular spectra that we’re getting off those diamonds.”

Photo: Photographed through the thick protective glass of the Hope Diamond’s exhibition case, Jeffrey Post returns the diamond to its pedestal in the Harry Winston Gallery of The Janet Annenberg Hooker Hall of Geology, Gems, and Minerals in the Smithsonian’s National Museum of Natural History. (Photos by Chip Clark)

Post’s work has already yielded knowledge of interest not just to scientists but to diamond sellers and their customers. Because the relative intensity of the blue and red components of each blue diamond’s phosphorescence is unique, the same sort of analysis that the researchers did in the museum vault might be used to fingerprint individual blue diamonds and to distinguish natural stones from man-made ones.

No stranger to spectacular gems, Post still gets a thrill from working with the Hope Diamond. “Every time I look at it I kind of go, ‘My gosh!,’” he says, noting that it is impossible to overlook the stone’s “human history, the curse and the kings, the queens, the thefts.”

However, the scientist believes that his recent research underscores the famous diamond’s importance as “a unique natural history object.”

SCIENCE BRIEF:Andes Mountains Are Older Than Previously Believed

John Barrat — Thu, 04 Jun 2009 19:59:23 +0000

The geologic faults responsible for the rise of the eastern Andes mountains in Colombia became active 25 million years ago—18 million years before the previously accepted start date for the Andes’ rise, according to researchers at the Smithsonian Tropical Research Institute in Panama, the University of Potsdam in Germany and Ecopetrol in Colombia.

“No one had ever dated mountain-building events in the eastern range of the Colombian Andes,” said Mauricio Parra, a former doctoral candidate at the University of Potsdam (now a postdoctoral fellow with the University of Texas) and lead author. “This eastern sector of America’s backbone turned out to be far more ancient here than in the central Andes, where the eastern ranges probably began to form only about 10 million years ago.”

The team integrated new geologic maps that illustrate tectonic thrusting and faulting, information about the origins and movements of sediments and the location and age of plant pollen in the sediments, as well as zircon-fission track analysis to provide an unusually thorough description of basin and range formation.

As mountain ranges rise, rainfall and erosion wash minerals like zircon into adjacent basins, where they accumulate to form sedimentary rocks. Zircon contains traces of uranium. As the uranium decays, trails of radiation damage accumulate in the zircon crystals. At high temperatures, fission tracks disappear like the mark of a knife disappears from a soft block of butter. By counting the microscopic fission tracks in zircon minerals, researchers can tell how long ago how long ago rocks began to be uplifted, or exhumed toward the earth surface.

Classification of nearly 17,000 pollen grains made it possible to clearly delimit the age of sedimentary layers.

The use of these complementary techniques led the team to postulate that the rapid advance of a sinking wedge of material as part of tectonic events 31 million years ago may have set the stage for the subsequent rise of the range.

“The date that mountain building began is critical to those of us who want to understand the movement of ancient animals and plants across the landscape and to engineers looking for oil and gas,” said Carlos Jaramillo, staff scientist from STRI. “We are still trying to put together a big tectonic jigsaw puzzle to figure out how this part of the world formed.”

This work was published in the Geological Society of America Bulletin in April 2009.

STRI, headquartered in Panama City, Panama, is a unit of the Smithsonian Institution. The institute furthers the understanding of tropical nature and its importance to human welfare, trains students to conduct research in the tropics and promotes conservation by increasing public awareness of the beauty and importance of tropical ecosystems. Web site: www.stri.org.