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from article Trilobita
Two iron-stained trilobites (Paradoxides) on a bedding plane slab from Morocco, North Africa, of Cambrian age. (Credit: Alan Morgan)
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from article Trilobita
Trilobite diversity and preservation. (a) Olenellid, Lower Cambrian (British Columbia). External mold of exoskeleton in shale. (b) Ogygopsis, Middle Cambrian (British Columbia). Molt assemblage, with cranidium and pygidium aligned, but librigenae,…
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from article Trilobita
Morphological features of trilobites. (a) Calymene, Silurian (New York). Dorsal view of mineralized exoskeleton. (b) Phacops, Devonian (Ohio). Ventral (bottom) view of cephalon and anterior segments of the thorax, with hypostome attached. (c)…
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from article Trilobita
Triarthrus eatoni, Upper Ordovician (New York). Reconstruction with dorsal exoskeleton removed on right side to show appendages. Antennae are incomplete. Exites (gill branches) of the first nine postantennal appendages are removed to show the…
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from article Siderite
Siderite specimen. (RF Company/Alamy)
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from article Forest fire
Exclusion of fire by humans has contributed to dramatic large blazes in the western United States. (Credit: Kari Greer)
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from article Forest fire
Crown fire in northern California. (Credit: Kari Greer)
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from article Forest fire
Values at risk during a forest fire can vary, depending on the location of the fire. (Credit: USDA Forest Service)
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from article Forest fire
Wildland firefighters work to separate the fuels on the ground from the fire in an effort to stop the spread of the fire. (Credit: Kari Greer)
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from article Forest fire
Engine crews work to suppress a large wildfire in northern California. (Credit: Kari Greer)
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from article Forest fire
Mega-fires often result in severe damage to natural resources and have long-lasting regional impacts. (Credit: USDA Forest Service)
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from article Forest fire
An example of fire prevention education: Smokey Bear. (Credit: USDA Forest Service)
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from article Forest fire
Lookouts in places where elevation and vision allow for a wide view of a broad expanse play an integral role in fire detection. (Credit: Kari Greer)
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from article Forest fire
Through a variety of management activities, societies seek to mitigate the impacts of wildfire. (A) Use of a masticator to reduce fuels. (B) Use of a low-intensity, prescribed (planned) fire to reduce the density of the vegetation, reduce fuels, and…
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from article Forest fire
Methods of fire suppression include hand crews, engine crews, and airborne intervention. While aircraft support firefighting efforts, forest fires are extinguished by ground-based firefighters. (Credit: USDA Forest Service)
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from article Forest fire
Extremely intense, fast moving forest fires can overwhelm even the most experienced, well-equipped firefighting workforce. (Credit: USDA Forest Service)
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from article Heat balance of the Earth
Heat balance of the Earth and the atmosphere system. The solar (SOL) constant used in the calculations is 1366 W/m2 so that the effective incoming solar flux is 342 W/m2, while the global albedo used is 30%. The atmosphere given in the figure…
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from article Heat balance of the Earth
Components of the annual mean absorbed solar flux, emitted infrared flux, and net radiative flux as functions of latitude at the top of the atmosphere derived from satellite broadband radiation measurements. (Data taken from K. N. Liou, 2002)
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from article Dasheen
Corms of dasheen (Colocasia esculenta). (Photo courtesy of Forest and Kim Starr)
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from article Cantaloupe
Cantaloupes (Cucumis melo var. reticulatus). (Photo by Scott Bauer, Agricultural Research Service, United States Department of Agriculture)
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from article Cancrinite
Cancrinite with biotite in nepheline syenite rock, Bigwood Township, Ontario, Canada. (Specimen from Department of Geology, Bryn Mawr College)
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from article Neomeniomorpha
Gymnomenia virgulata Scheltema from a depth of 620 m (2000 ft) off Walvis Bay, Namibia. (a) Entire specimen, anterior to right, long cilia extending from the pedal pit. (b, c) Posterior and anterior ends, respectively. (d) Ventral view of a,…
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from article East Indies
East Indies. The tinted areas represent the shallow continental shelves of Sundaland and northern Australia, drawn at the 660-ft (200-m) isobath. The western boundary of Wallacea is Wallace's Line of 1863. The eastern boundary is Lydekker's Line,…
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from article Plants of saline environments
Desert arrowweed (Pluchea sericea) is a halophytic evergreen shrub adapted for growth in the salty basins of Death Valley, California. (Credit: Steven P. Lynch)
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from article Plants of saline environments
Soluble salts in irrigation water and those present in fertilizers lead to the gradual accumulation of toxic levels of sodium ions in topsoil, rendering the land useless. (Credit: Roberto A. Gaxiola)
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from article Plants of saline environments
Relationship between growth and sodium chloride concentration for halophytes and glycophytes. The diagram assumes that the plants are growing in a culture solution that accounts for about 10–20 mol m−3 of ions. (Copyright © McGraw Hill)
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from article Plants of saline environments
Suaeda maritima (annual sea blite), a halophytic member of the Chenopodiaceae. (Credit: František Pleva)
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from article Plants of saline environments
Gray mangrove (Avicennia marina) on the island of Tonga. Aerial roots called pneumatophores, which act as a snorkel, are growing out of the mud. Other mangroves can absorb air through holes in their bark known as lenticels. (Credit: Valentina…
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from article Plants of saline environments
Salt gland from the mangrove swamp species Aegiceras corniculatum. (a) Secretory cells surrounded by cuticle and epidermal cells. (b) Section through the gland. (Copyright © McGraw Hill)
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from article Stratigraphy
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from article Stratigraphy
Conceptual cross sections in relation to (a) depth and (b) geological time showing stratal geometry, the distribution of silliciclastic facies and standard nomenclature for sequences associated with a shelf-slope break. Systems tracts: SMST, shelf…
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from article Monoplacophora
Living and fossil Monoplacophora. (a) Neopilina galatheae. (b) Tryblidium reticulatum. (After R. C. Moore, ed., Treatise on Invertebrate Paleontology, pt. I, 1957)
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from article Monoplacophora
Side views of various helcionellacean and bellerophont univalved mollusks. (a) Cyrtonellopsis; (b) Hypseloconus; (c) Cyclocyrtonella; (d) Stenotheca; (e) Bellerophon; (f) Tropidodiscus. (After B. Runnegar, Class Monoplacophora, in R. S. Boardman, A.…
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from article Gorgonacea
Gorgonian colonies in life. (a) Plumigorgia cf. hydroides, Palawan, Philippines. (b) Eunicella gracilis, São Tomé, Gulf of Guinea. (c) Junceella fragilis, Luzon, Philippines. (d) Leptogorgia alba, Cocos Island, Costa Rica. (e) Astrogorgia sp.,…
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from article Gorgonacea
Some common gorgonaceans. (a) Thouarella hicksoni (inset, detail of polyps). (b) Ideogorgia capensis. (c) Eunicella papillosa. (d) Leptogorgia lutkeni. (e) Junceella sp. (f) Anthothela parviflora. (g) Rumphella sp. (h) Homophyton verrucosum. (i)…
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from article Gorgonacea
Gorgonian colonies (dry preserved specimens). (a) Briareum sp. (b) Ideogorgia capensis. (c) Chrysogorgia pinnata. (d) Fanellia compressa. (e) Viminella sp. (f) Paragorgia sp. (g) Subergorgia suberosa. (h) Isis hippuris. (i) Solenocaulon sp.
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from article Gorgonacea
Caribbean gorgonian colonies (digital scans from dry preserved specimens). (a) Muricea cf. fruticosa. (b) Gorgonia ventalina. (c) Pseudopterogorgia cf. hummelincki.
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from article Gorgonacea
Gorgonian colonies (dry preserved specimens). (a) Leptogorgia palma. (b) Skeleton of Isidella sp. (Artwork courtesy of Jessica Machnicki, California Academy of Sciences)
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from article Gorgonacea
Gorgonian morphology.
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from article Meromictic lake
Cross-sectional diagram of a meromictic lake.
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from article Meromictic lake
The outlines show the maximum horizontal displacement of a radiotracer (sodium-24) following its release at 8-m (26-ft) depth in Stewart's Dark Lake, Wisconsin. The numbers indicate the hours elapsed after release.
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from article Polycladida
Examples of body form in acotylean polyclads. (a) A more common oval shape with midventral mouth and pharynx (Stylochus ellipticus). (b) A less common ribbon shape with a posteriorly positioned mouth and pharynx (Latocestus whartoni). (Illustration…
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from article Polycladida
Anatomy of Pleioplana atomata, a common acotylean polyclad of temperate waters. (Illustration courtesy of L. H. Hyman)
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from article Polycladida
Cycloporus, a large cotylean polyclad with anal pores. (Illustration courtesy of L. H. Hyman)
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from article Elephant
The African bush elephant (Loxodonta africana). (Credit: Robert Thomas and Margaret Orr; copyright © California Academy of Sciences)
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from article Cloud
Clouds as photographed by meteorological satellites. (a) A garden of thunderstorms, showing the anvils, forming at the tropopause inversion. (b) A hurricane, showing the eye. (c) Convective cloud over land and sea-breeze clouds.
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from article Cloud
Cirrus, with trails of slowly falling ice crystals at a high level. (F. Ellerman, U.S. Weather Bureau)
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from article Cloud
Small cumulus. (U.S. Weather Bureau)
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from article Cloud
Overcast of stratus, with some fragments below the hilltops. (U.S. Weather Bureau)
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from article Cloud
View from Mount Wilson, California. High above is a veil of cirrostratus, and below is the top of a low-level layer cloud. (F. Ellerman, U.S. Weather Bureau)
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from article Cloud
Cirrocumulus, high clouds with a delicate pattern. (A. A. Lothman, U.S. Weather Bureau)
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from article Cloud
Altocumulus, which occurs at intermediate levels. (G. A. Lott, U.S. Weather Bureau)
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from article Cloud
Altostratus, a middle-level layer cloud. Thick layers of such clouds, with bases extending down to low levels, produce prolonged rain or snow, and are then called nimbostratus. (C. F. Brooks, U.S. Weather Bureau)
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from article Cloud
Cumulonimbus clouds photographed over the upland adjoining the upper Colorado River valley. (Lt. B. H. Wyatt, U.S.N., U.S. Weather Bureau)
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from article Cloud
A cloud formed by moist air flowing over a mountain. Note the smooth upper profile, indicating low-turbulence flow. (Courtesy of John Hallet)
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from article Cloud
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from article Mesosphere
Structure of the mesosphere.
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from article Spruce
Cones of eastern and western spruce species. (a) Black spruce (Picea mariana). (b) Red spruce (P. rubens). (c) White spruce (P. glauca). (d) Colorado blue spruce (P. pungens). (e) Norway spruce (P. abies). (Brooklyn Botanic Garden)
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from article Spruce
Blue spruce (Picea pungens). (Photo courtesy of D. E. Herman, North Dakota State Soil Conservation Committee, USDA–NRCS PLANTS Database)
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from article Clay minerals
Diagrammatic sketch showing (a) single silica tetrahedron and (b) sheet structure of silica tetrahedrons arranged in a hexagonal network. (After R. E. Grim, Clay Mineralogy, McGraw-Hill, 1953)
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from article Clay minerals
Diagrammatic sketch showing (a) single octahedral unit and (b) sheet structure of octahedral units. (After R. E. Grim, Clay Mineralogy, McGraw-Hill, 1953)
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from article Clay minerals
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from article Map projections
Oblique Mercator projection on a cylinder. (After American Oxford Atlas, Oxford, 1951)
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from article Map projections
Conical projection, based on origin 45°N, 10°E. (After American Oxford Atlas, Oxford, 1951)
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from article Map projections
Azimuthal projections with tangent planes have been raised above the sphere surface. (a) Polar azimuthal. (b) Oblique azimuthal. (After American Oxford Atlas, Oxford, 1951)
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from article Map projections
Four pseudocylindrical projections. (University of Wisconsin-Madison Cartographic Laboratory)
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from article Map projections
The property of equivalence is not maintained on the Mercator projection, making Greenland and South America appear similar in size. The inset map shows that South America is actually about 15 times larger than Greenland.
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from article Heterocorallia
Morphology of the heterocorallian skeleton. (a) External view. (b) Transverse thin section. (c) Median longitudinal thin section. (d) Enlarged part of c. (After R. C. Moore, ed., Treatise on Invertebrate Paleontology, pt. F, Geological Society of…
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from article Heterocorallia
Details of the heterocorallian body. (a) Generalized pattern of septal insertion (from O. Schindewolf, Grundfragen der Paläontologie, Schweizerbart, Stuttgart, 1950). (b) Reconstruction of the mesenterial in the soft body (from M. Gudo,…
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from article Willow
Close-up view of peachleaf willow (S. amygdaloides). (Photo courtesy of Sheri Hagwood, USDA–NRCS PLANTS Database)
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from article Willow
White willow (S. alba). (Photo courtesy of D. E. Herman, North Dakota State Soil Conservation Committee, USDA–NRCS PLANTS Database)
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from article Sable
Sable (Martes zibellina). (Photo courtesy of Alex Kantorovich)
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from article Selachii
Caribbean reef shark (Carcharhinus perezi), a species of ground shark. (Getty Images copyright © Digital Vision)
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from article Tree physiology
Emory oak (Quercus emoryi) is an evergreen tree. (Credit: Homer Edward Price)
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from article Tree physiology
Sequoia (Sequoiadendron giganteum). The height of sequoia trees can reach 90 m (300 ft). (Credit: Anita Ritenour)
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from article Tree physiology
Cross section of a woody stem. (Copyright © McGraw Hill)
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from article River tides
Time series of predicted water level heights referenced to mean water level at four locations in the San Francisco Bay and Sacramento River system. Golden Gate is at the entrance to bay (km = 0); Chipps Island is 72 km (45 mi) up-estuary; Sacramento…
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from article Trophic ecology
Trophic ecology investigates the structure of feeding (trophic) relationships among organisms in an ecosystem. In general, feeding or trophic relationships are represented as a food web or as a food chain (often depicted as a pyramid). (Copyright ©…
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from article Trophic ecology
Food chain dynamics in subtidal kelp forests. Four-level trophic system: In open coastal areas, killer whales decimate sea otter populations, creating conditions in which urchins can regulate macroalgae. Three-level trophic system: In the absence of…
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from article Boring bivalves
A pholad shell: (a) external view, showing position of accessory plates and parts of the valve; (b) internal view, showing position of muscle and parts of the valves. (After R. D. Turner, The family Pholadidae in the western Atlantic and eastern…
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from article Boring bivalves
Typical boring bivalves: (a) Diplothyra smithii boring in Crassostrea virginica; (b) Penitella penita boring in shale; (c) Zirfaea crispata removed from burrow, showing foot, anterior adductor muscle, and siphons (from R. D. Turner, The family…
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from article Irrigation (agriculture)
Irrigation system in use, enabling crops to grow in an otherwise too-arid environment. (Credit: NASA)
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from article Irrigation (agriculture)
Furrow irrigation on romaine lettuce in Yuma, Arizona. (Credit: Jeff Vanuga, USDA Natural Resources Conservation Service)
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from article Irrigation (agriculture)
A center-pivot irrigation system in Mazowe, Zimabawe. (Credit: Ozman_Photography / Shutterstock)
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from article Carp
Mirror carp (Cyprinus carpio), showing a few large scales.
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from article Fire and disturbance ecology
Image taken in July 2012 showing the effects of a low-severity ground fire in a ponderosa pine (Pinus ponderosa)-dominated forest in the Sinlahekin Wildlife Area, Okanogan County, Washington. This was a prescribed fire and was applied to the…
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from article Fire and disturbance ecology
Image taken in October 2010 showing multiple fire scars in the tree rings of a cross section of a +400-year-old ponderosa pine (Pinus ponderosa) tree. The fire scars are the black curved lines near the bottom of the image. Each has been dated to the…
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from article Fire and disturbance ecology
Image showing a lake sediment core recovered from Sunrise Lake, Mount Rainier National Park, Washington, in August 2012. (Credit: Megan Walsh)
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from article Fire and disturbance ecology
Image showing a view of macroscopic charcoal under a stereomicroscope (approximately 40× magnification). Charcoal, which is created from the incomplete combustion of biomass, accumulates in lakes and wetlands following fire events and is preserved…
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from article Fire and disturbance ecology
Image showing the slow regrowth of a subalpine fir (Abies lasiocarpa)-dominated forest nearly 10 years after a high-severity, stand-replacing fire burned near Fish Lake in the Wallowa-Whitman National Forest, Oregon. (Credit: Megan Walsh)
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from article Fire and disturbance ecology
Image showing the cone of a lodgepole pine (Pinus contorta) that was heated, but not burned, during the September 2012 Table Mountain Fire near Ellensburg, Washington. Lodgepole pine cones are serotinous, meaning they are sealed with a waxy coating,…
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from article Fire and disturbance ecology
Image showing Oregon white oak (Quercus garryana) resprouting from the base of a tree burned in the August 2012 Taylor Bridge Fire near Ellensburg, Washington. This photo was taken in November 2012, only 2 months after the fire occurred, at which…
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from article Fire and disturbance ecology
Image showing the thickness of the bark on an old-growth Douglas-fir tree found in the Willamette National Forest, near Lowell, Oregon. Look near the middle of the trunk and you can see that the bark on this tree is almost 10 cm thick. (Credit:…
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from article Fire and disturbance ecology
Image showing the aftermath of the Taylor Bridge Fire, a stand-replacing fire that burned near Ellensburg, Washington, in August 2012. This forest, which is dominated by ponderosa pine (Pinus ponderosa), historically experienced frequent,…
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from article Graben
Diagram of simple graben. (After A. K. Lobeck, Geomorphology, McGraw-Hill, 1939)
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from article Cheilostomata
Cheilostome colonies and zooecia (scale of colonies, ×1). (a) Encrusting sheets of Membranipora and Electra on bivalve shell. (b) Erect, flat branches of Chartella. (c) Upper (frontal) surface section (scale, ×8) of encrusting sheet of…
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from article Cheilostomata
Anascan cheilostome zooid, showing soft parts and zooecium, with tentacles extended. (Reprinted with permission from R. J. Cuffey and J. E. Utgaard, Bryozoans, in R. Singer, ed., Encyclopedia of Paleontology, Fitzroy Dearborn, 1999)
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from article Cheilostomata
Arrangements of frontal walls in Cheilostomata. The X indicates the membrane that can be pulled by muscles in order to displace fluid/liquid that pushes the polypide (shaded) out so that the tentacles can feed in the space above the skeleton. (a)…
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from article Genetically engineered plants
Stalks of genetically engineered barley. This particular genetically engineered plant carries a gene that helps it to resist attack by barley yellow dwarf virus. (Credit: Jack Dykinga/Agricultural Research Service, U.S. Department of Agriculture)
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from article Genetically engineered plants
Plasmid vector schematic illustrating the common elements of a plasmid vector that is used to deliver the gene (or genes) of interest to plant cells that have been prepped for transformation. Depending on the transformation technique, the components…
