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A team of researchers analyzing high-resolution images obtained by the Lunar Reconnaissance Orbiter Camera (LROC) show small, narrow trenches typically much longer than they are wide. This indicates the lunar crust is being pulled apart at these locations. These linear valleys, known as graben, form when the moon’s crust stretches, breaks and drops down along two bounding faults. A handful of these graben systems have been found across the lunar surface.

Thomas Watters of the Smithsonian’s National Air and Space Museum discusses the lunar graben and what they reveal about how the moon evolved. (Credit: NASA’s Goddard Space Flight Center, Dan Gallagher)

“We think the moon is in a general state of global contraction because of cooling of a still hot interior,” said Thomas Watters of the Center for Earth and Planetary Studies at the Smithsonian’s National Air and Space Museum in Washington, and lead author of a paper on this research appearing in the March issue of the journal Nature Geoscience. “The graben tell us forces acting to shrink the moon were overcome in places by forces acting to pull it apart. This means the contractional forces shrinking the moon cannot be large, or the small graben might never form.”

The weak contraction suggests that the moon, unlike the terrestrial planets, did not completely melt in the very early stages of its evolution. Rather, observations support an alternative view that only the moon’s exterior initially melted forming an ocean of molten rock.

Right: This image shows the largest of the newly detected graben found in highlands of the lunar farside. The broadest graben is about 1,640 feet wide and topography derived from Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) stereo images indicates they are almost 20 meters (almost 66 feet) deep. (Credit: NASA/Goddard/Arizona State University/Smithsonian Institution)

In August 2010, the team used LROC images to identify physical signs of contraction on the lunar surface, in the form of lobe-shaped cliffs known as lobate scarps. The scarps are evidence the moon shrank globally in the geologically recent past and might still be shrinking today. The team saw these scarps widely distributed across the moon and concluded it was shrinking as the interior slowly cooled.

Based on the size of the scarps, it is estimated that the distance between the moon’s center and its surface shank by approximately 300 feet. The graben were an unexpected discovery and the images provide contradictory evidence that the regions of the lunar crust are also being pulled apart.

“This pulling apart tells us the moon is still active,” said Richard Vondrak, LRO Project Scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md. “LRO gives us a detailed look at that process.”

Left: This image shows the largest of the newly detected graben found in highlands of the lunar farside. The broadest graben is about 500 meters (1,640 feet) wide and topography derived from Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) stereo images indicates they are almost 20 meters (almost 66 feet) deep. (Credit: NASA/Goddard/Arizona State University/Smithsonian Institution)

As the LRO mission progresses and coverage increases, scientists will have a better picture of how common these young graben are and what other types of tectonic features are nearby. The graben systems the team finds may help scientists refine the state of stress in the lunar crust.

“It was a big surprise when I spotted graben in the far side highlands,” said co-author Mark Robinson of the School of Earth and Space Exploration at Arizona State University, principal investigator of LROC. “I immediately targeted the area for high-resolution stereo images so we could create a three-dimensional view of the graben. It’s exciting when you discover something totally unexpected and only about half the lunar surface has been imaged in high resolution. There is much more of the moon to be explored.”

The research was funded by the LRO mission, currently under NASA’s Science Mission Directorate at NASA Headquarters in Washington. LRO is managed by NASA’s Goddard Space Flight Center in Greenbelt, Md. –Source: NASA

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The researchers discovered periodic increases in the amount of the isotope strontium-87 found in marine fossils. The timing of these increases corresponds to previously discovered low points in marine biodiversity that occur in the fossil record roughly every 60 million years. Authors of the study are Adrian Melott, professor of physics and astronomy at the University of Kansas, paleobiologist Richard Bambach of the Smithsonian’s National Museum of Natural History, Kenni Petersen of Aarhus University, Denmark, and John McArthur of University College London.

Image right: Yosemite Valley and Half Dome from Glacier Point. (Photo by Jon Sullivan)

Melott, lead author, thinks the periodic extinctions and the increased amounts Sr-87 are linked. “Strontium-87 is produced by radioactive decay of another element, rubidium, which is common in igneous rocks in continental crust,” Melott says. “So, when a lot of this type of rock erodes, a lot more Sr-87 is dumped into the ocean, and its fraction rises compared with another strontium isotope, Sr-86.”

An uplifting of the continents, Melott explains, is the most likely explanation for this type of massive erosion event.

“Continental uplift increases erosion in several ways,” he said. “First, it pushes the continental basement rocks containing rubidium up to where they are exposed to erosive forces. Uplift also creates highlands and mountains where glaciers and freeze-thaw cycles erode rock. The steep slopes cause faster water flow in streams and sheet-wash from rains, which strips off the soil and exposes bedrock. Uplift also elevates the deeper-seated igneous rocks where the Sr-87 is sequestered, permitting it to be exposed, eroded, and put into the ocean.”

The massive continental uplift suggested by the strontium data would also reduce sea depth along the continental shelf where most sea animals live. That loss of habitat due to shallow water, Melott and collaborators say, could be the reason for the periodic mass extinctions and periodic decline in diversity found in the marine fossil record.–Source: University of Chicago Press Journals

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Richard Wunderman is managing editor of the Bulletin of the Global Volcanism Network and a geologist in the Division of Mineral Sciences at the Smithsonian’s National Museum of Natural History. Following the earthquake that rumbled across the East Coast of the United States on Aug. 23, Smithsonianscience.org asked Wunderman a few questions about earthquakes and how scientists measure and assess them. He was assisted by interns Claire Hepper and Robert Dennen.

Q. The earthquake that struck the Washington, D.C. area on Tuesday, Aug. 23, was 5.8 magnitude. Why did the earthquake occur? How do scientists assess earthquake size and impact?

A. The Virginia earthquake released energy stored as accumulated stress in the crust along faults along the coastal side of the Appalachian mountains. The resulting shock waves were felt by people into Canada and Georgia. The main areas of damage were strongest near the epicenter, the point on the Earth’s surface above the earthquake, and minor damage in urban areas at distance, such as Washington D.C. located 85 mi. northeast of the epicenter.

Figure right:  Generalized geologic map showing the location of the M 5.8 EQ of 23 August 2011. The areas in white are ancient rocks of the Appalachian region that transmit seismic energy efficiently. Some other smaller epicenters also shown. Map taken from blog by C.M. Bailey 2011 (Click image to enlarge).

The cause of the stress is plausibly attributed to factors such as ancient mountain building along the East side of the Appalachian mountains, more recent shifts and adjustments in this region, or from stress developed in more recent times. Virginia’s Division of Geology and Mineral Resources has excellent resources here.

Q. The energy released during the earthquake was stress that had been building up along a fault line in central Virginia for a very long time. Now that this stress has been released, can we relax and not expect another quake for many, many years?

A. Yes, we would assume that along the fault where the earthquake occurred, this might help alleviate another large earthquake there. Trouble is, some of this stress has probably shifted to another area on this or adjacent faults. A complex web of short faults has been mapped in the region.

That being said, the last large earthquake was around 114 years ago, also a magnitude 5.8 quake, so it is seems unlikely that there will be another in the near future. Small earthquakes, which cause little to no damage, have been an almost yearly occurrence in the Virginia seismic area and will likely continue at that recurrence interval.

Q. On Aug. 23, the shaking in Washington, D.C. seemed to last only 20 seconds. Is duration one of the characteristics of an earthquake that is used to measure its magnitude?

A. The size of the earthquake is a potentially confusing topic so I’ll start at a point that everyone can relate to. That is, a general sense of the shaking levels from an earthquake, an estimate called intensity. This measure does not rely on instruments and much in the way of numerical measurements, but addresses the important question of what the shaking actually did.

Yes, the damage could indeed relate to duration of the shaking. And, yes, prolonged duration could spell disaster. Other factors could include the earthquake’s focal depth, its peak accelerations, the kinds of waves generated and their frequencies. Relating to the site, factors include the thickness and kind of crustal material through which the shock waves passed, the local rock and soil types, the slope, and water saturation of the ground. Other critical factors include local rocks and structures such as buildings, bridges, and dams, and how they respond.

Earthquakes can range from not felt and no impact, all the way to leveling large areas, causing secondary effects like substantial tsunamis, landslides, and liquefaction (shaking wet sand, mud, or soils such that it flows, almost like water). The most common intensity scale is the Modified Mercalli scale.

Akin to the intensity scale, the U.S. Geological Survey also employs a system called the “felt magnitude.” This is estimated from personal accounts, and basically asks “how strong did the earthquake feel?” In this estimate, the way an earthquake is perceived by individuals is the measure of the earthquake magnitude, and one person may base their interpretation of the earthquake magnitude on the duration or any other characteristic. The USGS compiled “felt magnitude” for the Aug. 23 Virginia earthquake can be viewed here.

Magnitude, as in an M 5.8 earthquake, represents a scale based on the readings from seismometers and the wave traces we call seismograms. There are various kinds of these magnitude scales (eg. the Richter scale) and the magnitudes are often based on the size of the largest waves received (rather than the duration of the earthquake’s waves).

Figure left: A simplified illustration of earthquake-triggered waves and the resulting seismogram from a site at distance (at left; tracing time on the x-axis and amplitude on the y-axis). The seismogram contains labels indicating the first arrival of waves; the largest amplitude waves in the case shown are waves traveling along the ground surface called Rayleigh waves. The depiction omits the wave paths moving to the left (as well as some other waves). Taken from Stein and Wysession (2003; their online PowerPoint presentation for Chapter 1 of An Introduction to Earthquakes, Seismology, Earthquakes, and Earth Structure).

The distance from the earthquake and its depth are first calculated, and then the instrument readings at various distances from the epicenter are compensated for, and in fact, there are many corrections and assumptions. These values are often computed from multiple stations using computers. They are often refined somewhat, based on new information and various corrections. Comparisons between intensity and magnitude scales are inexact.

Q. Earthquakes by their very nature are relatively short-lived events, over in a few seconds . . . correct? Or do some earthquakes last a long time?

A. Generally the shaking of the Earth as a result of the fracturing along the fault lasts only a few seconds. That said, in a large earthquake, the propagating waves from the fault rupture can shake for minutes, since for one thing, they come from various parts of the fault and also because the waves reflect (bounce around), actually probing the reaches of the entire planet and providing key clues to the various inner parts of the planet (crust, mantle, and two-part core).

Thick sedimentary valleys and basins such as found in many Western USA settings can behave somewhat like jello, and shake much longer (and stronger, that is, with higher amplitude) than the initial passing waves, essentially amplifying the earthquakes intensity.

Weak vibrations triggered by strong earthquakes may cause the entire planet to ring like a bell at amplitudes and frequencies detected instrumentally but not felt by people. This ringing can go on for weeks in the case of a strong earthquake.

Aftershocks, which are the Earth settling and readjusting, can recur sporadically for weeks to more than a decade after an earthquake has occurred, generally diminishing with time in number and strength.

Q. Much of the structural damage to buildings caused by the Aug. 23 earthquake, it seems, occurred to areas that are high up–cracks at the top of the Washington Monument, the spires of the National Cathedral, and the towers and chimneys of the Smithsonian Castle. Why is that?

A. Hold a stiff fishing pole by the handle and oriented vertically. If you give the handle a shake, the rod’s tip will move as the waves arrive, and excursions there will be comparatively large. Structures made of, or faced with stone, offer special challenges, as the ‘building blocks’ they may not hang together during the deformation and shaking.

Image right and above: The Aug.23 earthquake caused damage to the chimneys and other high-up structures on the east end of the Smithsonian Castle. (Photos by Mark Avino and Eric Long)

Q. Is there a way to keep track of how much compression or tension is building up between rock plates on either side of a fault line?

A. There are multiple things than can be measured to keep track of offset along a fault over time. Strain meters measure the amount of strain (the movement or deformation caused by stress) present in the ground. Methods employing GPS or radar look at ground-surface deformation. One of my favorite methods is a simple line of survey monuments across arranged across a fault, repeatedly re-surveyed over time. After an earthquake, features such as roads, fences, and railroad tracks can record earthquake offset. You can see other famous examples here.

(Image left. A photo of an offset fence seen soon after the M 7.8 Great San Francisco earthquake of 1906. The San Andreas fault’s surface trace is drawn as a colored band. This area is now part of Point Reyes National Seashore. Image from Stein and Wysession 2003; online PowerPoint presentation).

Q. Where were you when the earthquake struck and what were your immediate thoughts?

A. I was at my desk in the Smithsonian’s Museum of Natural History on the Mall. Shaking grew to the point where it upset me as some of my geologic colleagues screamed and I heard glassware breaking. No one was hurt. In this commotion I had walked from my desk and braced myself in the office doorway, but the shaking stopped soon after that. As the event had escalated, my thoughts went to the building’s masonry construction and the well known, water-saturated fill in this part of the low-lying Washington, D.C. region. Neither of those thoughts were comforting, but the building withstood the stress without serious damage.

My wife and daughter were in the family car stopped at a traffic light when they felt weird unexplained vibrations. My wife immediately asked my daughter ‘What did daddy do to the car now?’ She attributed the vibration to engine or suspension trouble caused by you-know-who. The announcements of the earthquake saved me from near-certain allegations of car abuse.

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In a new study  in the journal Palaeontology, University of Florida and Smithsonian Tropical Research Institute scientists describe a new 20-foot extinct species discovered in the same Colombian coal mine with Titanoboa, the world’s largest snake. The findings help scientists better understand the diversity of animals that occupied the oldest known rainforest ecosystem, which had higher temperatures than today, and could be useful for understanding the impacts of a warmer climate in the future.

Image right: This illustration shows how Acherontisuchus guajiraensis, a 60-million-year-old ancestor of crocodiles, would have looked in its natural setting. Titanoboa, the world’s largest snake, is pictured in the background. (Illustration by Danielle Byerley/click to enlarge)

The 60-million-year-old freshwater relative to modern crocodiles is the first known land animal from the Paleocene New World tropics specialized for eating fish, meaning it competed with Titanoboa for food. But the giant snake could have consumed its competition, too, researchers say.

“The younger individuals were definitely not safe from Titanoboa, but the biggest of these species would have been a bit much for the 42-foot snake to handle,” said lead author Alex Hastings, a graduate student at the Florida Museum of Natural History and UF’s department of geological sciences.

Image left: University of Florida researchers unearth fossils from the 60-million-year-old Cerrejon formation in northeastern Colombia, one of the world’s largest open-pit coal mines. (Photo by Edwin Cadena)

The new species is a dyrosaurid, commonly believed to be primarily ocean-dwelling, coastal reptiles. The new adult specimens challenge previous theories the animals only would have entered freshwater environments as babies before returning to sea.

Fossils of a partial skeleton of the species, Acherontisuchus guajiraensis, show dyrosaurids were key players in northeastern Colombia and that diversity within the family evolved with environmental changes, such as an asteroid impact or the appearance of competitors from other groups, said Christopher Brochu, an associate professor of vertebrate paleontology in the department of geoscience at the University of Iowa, who was not involved in the study.

“We’re facing some serious ecological changes now,” Brochu said. “A lot of them have to do with climate and if we want to understand how living things are going to respond to changes in climate, we need to understand how they responded in the past. This really is a wonderful group for that because they managed to survive some catastrophes, but they seemed not to survive others and their diversity does seem to change along with these ecological signals.”

Image left: This photograph shows the size difference in the jawbones of two 60-million-year-old crocodile ancestors found in northeastern Colombia by University of Florida researchers.The newly described Acherontisuchus guajiraensis, top, and Cerrejonisuchus improcerus, bottom. C. improcerus was the first ancient crocodyliform found in the Cerrejon open-pit coal mine. The new species is the first known land animal from the Paleocene New World tropics specialized for eating fish. (Photo by Kristen Grace)

The species is the second ancient crocodyliform found in the Cerrejon mine of northern Colombia, one of the world’s largest open-pit coal mines. The excavations were led by study co-authors Jonathan Bloch, Florida Museum associate curator of vertebrate paleontology, and paleobotanist Carlos Jaramillo of the Smithsonian Tropical Research Institute.

“This one is related to a group that typically had these long snouts” Hastings said. “It would have had a relatively similar diet to the other (coastal) species, but surprisingly it lived in a more freshwater environment.”

The genus is named for the river Acheron from Greek mythology, “the river of woe,” since the animal lived in a wide river that emptied into the Caribbean. Unlike the first crocodile relative found in the area, which had a more generalized diet, the snout of the new species was long, narrow and full of pointed teeth, showing a specialization for hunting the lungfish and relatives of bonefish that inhabited the water.

“The general common wisdom was that ancestrally all crocodyliforms looked like a modern alligator, that all of these strange forms descended from a more generalized ancestor, but these guys are showing that sometimes one kind of specialized animal evolved from a very different specialized animal, not a generalized one,” Brochu said. “It’s really showing us a level of complexity to the history that 10 years ago was not anticipated.”

During the Paleocene in South America, the environment was dominated by reptiles, including giant snakes, turtles and crocodiles. The dyrosaurid family originated in Africa about 75 million years ago, toward the end of the age of dinosaurs, and arrived in South America by swimming across the Atlantic Ocean.

“The same thing that snuffed out the dinosaurs killed off most of the crocodiles alive at the time,” Hastings said. “The dyrosaurids are one of the few groups to survive the extinction and later become more successful.”

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Images right and below: Rough diamonds

“It’s very rare to know where some rough diamonds came from because typically, once they come out of the mine, they go to market and are sold,” says Jeffry Post, curator in the Department of Mineral Sciences. “In most cases, diamonds lose any documentary links to their source by the time they reach the market.” This donation will be a great asset to researchers, allowing them to study specimens and knowing where they originated in the Earth.

The larger diamonds in the Jewelers Mutual donation will be added to the diamond exhibition in the Natural History Museum’s Gem and Mineral Hall. The others will be made available for scientific study. Jewelers Mutual originally acquired the diamonds to display in the company’s onsite gallery of gems and minerals in Neenah.

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