Earth Science Picture of the Day

Chondrite Thin Section

2013-05-24T03:01:00-04:00

Photographer: Mila Zinkova
Summary Author: Mila Zinkova

Chondrites are perhaps the most interesting of all asteroid fragments. They constitute more than 80 percent of the meteorites observed to fall to Earth and derive their name from the chondrules virtually all of them contain. Chondrules are tiny beads of melted material, often smaller than a rice grain, that actually formed before asteroids took shape early in our solar system's history. Chondrite thin sections examined under a microscope are beautiful to behold – they’re not unlike some of the paintings by Wassily Kandinsky and other abstract artists. Seeing them close up is like discovering a striking new galaxy.

The above image is a thin section of chondrite meteorite NWA4637. I asked Dr. Alan Rubin to describe the image for EPOD readers, and he kindly agreed. He explains: "This is a type-3, L-group ordinary chondrite. The chondrules are well defined; they display a variety of textures and have experienced very little metamorphic heating. At upper left is a large, brown cryptocrystalline chondrule, composed of separate domains of tiny low-calcium pyroxene crystals surrounded by glass. The light-colored rim around the chondrule is a ‘bleached zone’ altered by the water of the parent asteroid. A smaller porphyritic olivine-pyroxene chondrule is at its lower right. The colorful grains are olivine, the gray grains, are low-calcium pyroxene. To the left of center is a radial pyroxene chondrule made up of low-calcium pyroxene laths arranged in a fan-like array. Part of a barred olivine chondrule can be seen at the extreme right center."

This image represents but a small portion (approximately 1.8 cm by 1 cm) of a single thin section, taken by using a microscope and cross-polarizing filters. The colors of the crystals will change depending on how the filters are rotated, so thin sections of chondrites contain seemingly limitless universes for one to explore.

Elephant Skin Weathering

2013-05-23T03:01:00-04:00

Photographer: David K. Lynch; Dave's San Andreas Fault Web site
Summary Author: David K. Lynch

Many massive carbonate rocks like limestone, marble and dolomite show elephant skin weathering, so called because of its resemblance to the rough, weathered hide of elephants. This weathering starts out as minute, random cracks in the rock that are exposed to rainwater. Rainwater is slightly acidic because atmospheric carbon dioxide (CO₂) dissolves in water (H₂O) to form carbonic acid (H₂CO₃). This slightly acidic rainwater then seeps into the cracks and dissolves a thin layer of limestone, converting it to calcium bicarbonate. The bicarbonate remains in solution and runs off, thereby leaving an enlarged crack. Over many years, the cracks deepen and widen, resulting in the aptly named surface. Elephant skin weathering in found almost exclusively on fine-grained carbonate rocks.

These specimens were found in the Soda Mountains near Baker, California. Notice that the rock fractured and broke along one of the enlarged cracks (missing fragment next to the penny). Photo taken on April 27, 2013.

Photo details: Camera Model: PENTAX K-x; Lens: smc PENTAX-DA 18-250mm F3.5-6.3 ED AL [IF]; Focal Length: 142.5mm (35mm equivalent: 214mm); Aperture: f/8.0; Exposure Time: 0.0050 s (1/200); ISO equiv: 1600; Software: K-x Ver 1.00.

Coral Pink Sand Dunes State Park

2013-05-22T03:01:00-04:00

Photographer: Steven Poole
Summary Authors: Steven Poole; Jim Foster

The view above shows the colorful sand dunes in Coral Pink Sand Dunes State Park, Utah. This is the only major sand dune field on the Colorado Plateau. It's estimated to be between 10,000 and 15,000 years old. The dunes formed as Navajo sandstone eroded in the Late Triassic or Early Jurassic, 225 million years ago. Persistent winds and the peculiar geographic orientation of terrain features steered the sand into the valley on leeward side of Moquith Mountain and Moccasin Mountain. The funneling effect of wind squeezing through the slot between these mountains accelerated the wind velocity, allowing even large sand grains to be lifted and redeposited miles away from the original sandstone outcrops. Coral and pink hues are attributed to the presence of iron oxides. Photo taken on April 9, 2013.

Photo details: Camera Maker: Panasonic; Camera Model: DMC-ZS19; Focal Length: 27.6mm (35mm equivalent: 154mm); Aperture: f/5.4; Exposure Time: 0.0013 s (1/800); ISO equiv: 100; Software: Ver.1.0.

Bonneville Salt Flats and Pilot Peak

2013-05-21T03:01:00-04:00

Photographer: Ray Boren
Summary Author: Ray Boren

A thin layer of pooled, mineral-laden water bathes and slowly sculpts a portion of the Bonneville Salt Flats, east of the twin desert towns of Wendover, Utah, and West Wendover, Nevada. The sheen slightly reflects the vault of the blue sky, as shown in the photograph above, taken on April 23, 2013. Nevada’s snow-topped Pilot Peak rises in the distance, peeking over the brown and mostly barren Silver Island Mountains, which are on the Utah side of the state line.

Winter and springtime snow and rainfall replenish and revive the surface minerals, including sodium chloride (table salt), potassium and magnesium that compose the Bonneville Salt Flats; a 159 sq mi (412 sq km) pan left behind by the prehistoric waters of vanished Lake Bonneville. The ancient lake covered much of western Utah and eastern Nevada during the Pleistocene ice ages. Due to climate change and geologic factors, the great lake dried up thousands of years ago, leaving behind only encrusted basins like this and a notable remnant, the Great Salt Lake. The salt plain is so extensive and flat that in late summer and fall, when the standing water has evaporated, racing aficionados bring their powerful vehicles to the Bonneville Speedway, hoping to break speed barriers and achieve land speed records –- a tradition here that dates back a century. Moreover, on a number of days layers of air trapped near the surface act as lenses, creating liquid-seeming mirages. As the British rock band Yes sang long ago in “Roundabout”: “Mountains come out of the sky and they stand there.”

Distant Pilot Peak was an important sentinel for trail-blazing 19th-century explorers and pioneers headed to California across the sterile and mucky Great Salt Lake Desert. Among these were members of the ill-fated Donner-Reed Party, whose oxen and wagons bogged down a short distance away in 1846. The pioneer company lost valuable time and resources, which led to tragedy when the expedition was caught by snowstorms in the Sierra Nevada range, 400 mi (640 km) to the west.

Photo details: Camera Model: NIKON D60; Focal Length: 12.0mm; Aperture: f/8.0; Exposure Time: 0.0013 s (1/800); ISO equiv: 100; Software: QuickTime 7.6.4.

Halo and Rainbow Panorama

2013-05-20T03:01:00-04:00

Photographer: Michael Grossmann; Michael's Web site
Summary Author: Michael Grossmann

It's rare that you can see a rainbow and halo simultaneously. However, on this early spring day in Kaempfelbach, Germany, such a feat was possible. During the late afternoon, as a brief rain shower developed in the eastern sky, a rainbow could be detected at the antisolar point -- near the eastern horizon (left). At the same time, sunlight refracting through randomly oriented ice crystals, composing a layer of cirrus clouds in the vicinity of the Sun (in the western sky, at right), triggered a bright 22 degree halo. Note that the camera is facing south. Photo taken on April 10, 2013.

Moqui Marbles and Martian Blueberries

2013-05-19T03:01:00-04:00

Photographer: Bret Webster; Bret’s Web site; Bret’s Facebook page
Summary Author: Bret Webster

The photo above shows Moqui Marbles in their native habitat of southern Utah. These curious rocks are actually concretions having iron (hematite) rinds. Very similar rocks, called blueberries, have been observed repeatedly on Mars by the rovers. Click here to see an image taken by the Opportunity rover of the blueberries. Some scientific papers implicate the possibility of life on Mars playing a role in their formation while others do not. Discussions about the pros and cons of their formation have been quite lively at times. However, the consensus seems to be that both the marbles and the blueberries were created beneath the surface as naturally occurring substances, most likely minerals, precipitated from flowing groundwater. Pictured with the marbles is a Devil's-Claw cactus (Sclerocactus parviflorus).

Photo details: Camera Model: Canon EOS 5D Mark II; Lens: EF24-105mm f/4L IS USM; Focal Length: 24mm;
Focus Distance: 0.64m; Aperture: f/8.0; Exposure Time: 0.0013 s (1/800); ISO equiv: 200; Software: Adobe Photoshop CS5.1 Windows.

Deep Blue Abyss on Godwin's Glacier

2013-05-18T03:01:00-04:00

Photographer: Julian Kegel; Julian's Web site
Summary Authors: Julian Kegel; Jim Foster

The photo above shows an amazing crevasse I stumbled upon while guiding hikers on a rainy summer's day on Godwin Glacier in Chugach National Forest, Alaska. I called it Godwin's Abyss. The entire crevasse is over several thousand feet long. The widest section, featured here, I estimated to be 60-70 ft across (18-21 m). Because this area of the ice was probably under the most stress, it opened very quickly and very recently, maybe even the night before we arrived. We know this because both rain and sunlight can decay solid glacier ice. When this happens, the ice looks particularly bright because the resulting air bubbles within the ice are quite effective at scattering light, much like in the head of a beer.

The beauty of this crack is not just the deep blue color emanating from the depths, but the fact that it's so deep (it's not known exactly how deep) the chasm appears to swallow light almost completely. In actuality, there are few air bubbles deep inside a glacier to reflect light back out, and the thick ice is absorbing nearly all wavelengths of visible light. Never in my many years of guiding had I ever seen such a magnificent gradient of color! Photo taken on July 27, 2011.

Photo details: Camera Model: Canon EOS 5D Mark II; Lens: EF50mm f/1.4 USM; Focal Length: 50.0mm; Aperture: f/18.0; Exposure Time: 0.013 s (1/80); ISO equiv: 800.

Fern-like Stellar Dendrite Snow Crystals

2013-05-17T03:01:00-04:00

Photographer: Jennifer Seay Campbell; Jennifer’s Web site
Summary Author: Brian Campbell

The photos above show some of the delicate snowflakes that fell during a light snowfall on the night of February 2, 2013, in Salisbury, Maryland. The flakes, fern-like stellar dendrites, were huge; the biggest we’d ever seen. Jennifer, a middle school math teacher by day and also a professional photographer said, "Look at these snowflakes, I need to grab my camera!" Snow fell for about 30 minutes -- the air temperature was approximately 30 F (-1.0 C). Grabbing a chair from the kitchen table, Jennifer went out onto our deck, laid a black fabric on the deck railing and began snapping pictures (gloveless) for around 20 minutes. She used a 100 mm macro lens, a lens she purchased just to take close-ups of wedding rings.

Stellar dendrites are perhaps the largest snowflakes that fall to Earth. They’re individual crystals, not multiple flakes stuck together, and may be 5 mm or more across. Because of their wafer-like structure, snow composed of these very thin crystals can be quite powdery, even at temperatures only slightly below freezing.

Photo details: TOP - Camera Model: Canon EOS 5D Mark III; Lens: EF100mm f/2.8L Macro IS USM; Focal Length: 100mm; Focus Distance: 0.29m; Aperture: f/3.5; Exposure Time: 0.017 s (1/60); ISO equiv: 12800; Software: Adobe Photoshop CS5 Windows. Bottom - same except: Focus Distance: 0.3m; Exposure Time: 0.0050 s (1/200). Photos color corrected with Adobe Camera Raw software in Photoshop. Note that the only light source was a spotlight – photos were taken at night.

Earth's Rotation and Polaris

2013-05-16T03:01:00-04:00

Photographer: John Chumack; John’s Web site
Summary Author: John Chumack

I captured this image of circumpolar star trails from the Cincinnati Astronomy Club’s Dark Sky location in Adams County, Ohio. Polaris, the North Star, is at center. The circular trails result from the Earth’s natural rotation – stars that never rise or set are said to be circumpolar. So how fast are we spinning? Well that depends on where on Earth you’re standing. I took this photo from 38.8 degrees north latitude, so in this 11 minute exposure, the Earth is spinning at about 800 mph (1,288 k/h). For someone on the equator, the spin rate increases to about 1,037 mph (1,670 k/h). Whether or not a star is actually circumpolar is a function of the observer’s latitude. For instance, any star at my location will be circumpolar if it’s less than about 39 degrees from Polaris. At the left side of the image (top to bottom), notice the blurred remnants of our Milky Way. The faint red dashed line running top to bottom near the center of the image is a jet aircraft. Photo taken on December 13, 2012.

Photo details: Camera Model: Canon EOS 40D; Focal Length: 17mm; Aperture: f/4.0; Exposure Time: 669.000 s; ISO equiv: 640; a single 11 minute exposure. Software: Adobe Photoshop 7.0.

Green and Blue Flashes

2013-05-15T03:01:00-04:00

Photographer: Oliver Stiehler
Summary Authors: Oliver Stiehler; Jim Foster

When taking photos of a sunset earlier this spring, I happened to catch these scintillating green and blue flashes -- mock mirages. The sky was cloudless with very little haze, and I was at a location approximately 900 ft (275 m) above sea level. With patience, a clean sky and a clear view of the horizon, green and even blue flashes can on occasion be observed at sunset and sunrise. They’re easier to detect at sunset since you don’t have to guess the exact spot where the solar disk will break the horizon.

The flashes result from atmospheric refraction when the Sun is low in the sky. But the refraction must be sufficiently strong, through atmospheric temperature gradients, that a mirage occurs. When this happens there's a marked vertical magnification of the images for parts of the mirage. Then, and only then, will color separation produced by differential refraction be visible to the eye or camera. Of course, always use extreme caution when looking toward the Sun. Photo taken on March 2, 2013.

Photo details: APO Televid 82 with DSLR adapter; a focal length of about 800 mm; aperture of f/9.8; 1/8000 second exposure; ISO 100, photos cropped to 35 percent of the original size.