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Terrestrial Origins and Evolution
A 3-D structure of RNA. Credit: SpaceDaily
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Portland State University Professor of Chemistry Niles Lehman.
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Scientists speculate that, before life took hold, an "RNA World" existed on early Earth, in which elementary RNA formed and reproduced spontaneously. Credit: NASA
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The remote Cuatro Ciénegas valley is located in the Chihuahuan Desert in northeast
Credit: The Nature Conservancy
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A comb jelly. The evolutionary history of the comb jelly has revealed surprising
clues about Earth's first animal.
Credit: Casey Dunn
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The comb jelly could only have achieved its apparent seniority over the simpler
sponge via one of two new evolutionary scenarios: 1) the comb jelly evolved its
complexity independently of other animals, after it branched off onto its own
evolutionary path; or 2) the sponge evolved its simple form from more complex
creatures--a possibility that underscores the fact that evolution is not necessarily
just a march towards increased complexity, says Dunn. This scenario would provide a
particularly dramatic example of that principle.
Credit: Zina Deretsky, NSF
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These cliffs at Zumaia in Spain's Basque country date to the end of the
Cretaceous. Sediment layers in the cliffs can yield information about
changes in Earth's climate.
Credit: PNAS / UC Berkeley
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Do minerals evolve? This image is of quartz crystals that grew out of mineral-rich solutions in large rock cavities. Such can grow quickly or slowly –” or even stop –” depending on changes in temperature and the concentration of the solution. Photo credit: The Smithsonian National Museum of Natural History.
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Dolphin mothers and their calves. The Wild Dolphin Project has been using intelligence tests on wild dolphins in the Bahamas. Phot credit: Denise L. Herzing.
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Peter Ungar of the University of Arkansas applies dental-impression
material to the jaw of Australopithicus afarensis, also known as Lucy.
Credit: University of Arkansas
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The first specimen found of P. boisei is what is known as the 'OH 5'
skull. This skull was discovered in Tanzania's Olduvai Gorge in 1959 by
Mary Leakey.
Credit: Smithsonian, National Museum of Natural History
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Scientists have found that rocks beneath the seafloor are teeming with microbial life.
Credit: Nicolle Rager-Fuller/National Science Foundation
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Bacteria form large undersea mats in some areas of the ocean's deepest realms.
Credit: Ridge2000/National Science Foundation
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Rocks made of basalt on and under the ocean bottom harbor surprising numbers of deep-sea bacteria.
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The bdelloid rotifer Philodina roseola (ca 400 microns).
Credit: Harvard, Department of Molecular and Cellular Biology
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A three-dimensional view of a model protocell approximately 100 nanometers in diameter.
Credit: Janet Iwasa, Szostak Laboratory, Harvard Medical School and Massachusetts General Hospital
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Harry Jerison plot of the encephalization quotient of animals
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This artist's conception shows the supercontinent Rodinia as it began to fragment. What became modern North America lies in the center of the landmass.
Image Credit: Tomo Narashima
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This is a TEM image taken of the water, or inclusion brine, inside the halite crystals. It's easy to see that the brine is full of fibers.
Credit: Griffith et al., 2008
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Ancient cellulose fibers were also collected from solid halite by centrifugation and photographed using a TEM microscope.
Credit: Griffith et al., 2008
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The structure of RNA and its chemical relative, DNA. Courtesy of NIH
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A 3D model of RNA.
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A magnified view of a microfluidic chip in which billions of RNA enzymes were made to undergo hundreds of generations of Darwinian evolution, under computer control. The active circuit, filled with blue dye, is 1 cm in diameter and contains five microvalves that are operated. Credit: Brian Paegel, The Scripps Research Institute
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Ronald Breaker and the chemical structure of cyclic di-GMP.
Credit: Yale
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Type I midshipman males, center, build and defend nests under rocky shelters and vocalize to court females, right, with a call known as a "hum." Smaller type II "sneaker" males, left, do not vocalize to court females, but rather try to sneak into the nest and steal fertilizations from type I males.
Credit: Cornell University
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Optical photomicrographs of a polished thin section of well-preserved microfossils from the approximately 0.85 billion year old Bitter Springs Formation of central Australia. Red box indicates portion shown in NanoSIMS image. Credit: Dorothy Oehler
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A NanoSIMS instrument at California Institute of Technology.
Courtesy Laurent Remusat
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A NanoSIMS analysis of the Bitter Springs sample shows the correspondence of carbon and nitrogen concentrations, suggesting the presence of a cell wall. Study was done on the Cameca NanoSIMS 50 instrument in the National Museum of Natural History in Paris in collaboration with Dr. Francois Robert, head of the Laboratory for the Study of Extraterrestrial Materials (LEME), and French colleagues in LEME. Credit: Dorothy Oehler
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Arrows on this electron microscope image indicate biofilms, or slime, peeling away from the walls of vascular canals in dinosaur bone.
Credit: Thomas Kaye, University of Washington
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The water boatman uses a thin layer of air as an "external lung" allowing it to breathe underwater.
Credit: John Bush and Morris Flynn, MIT
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The Fisher spider Dolomedes triton uses an air layer, approximately 0.2 mm thick, as an oxygen supply.
Credit: John Bush and Morris Flynn, MIT
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Green, right, works with Lise Ovreas, a scientist with the University of Bergen (Norway) Centre for Geobiology, to obtain microbes at Svalbard, an island in a Norway-controlled archipelago about 300 miles south of the North Pole.
Credit: Steve Coulson/OU
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Trichoplax adhaerens
Image Credit: Ana Signorovitch, Yale University
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Researchers examined ratios of carbon isotopes in a number of ocean sites, including the Pacific Ocean waters near Australia's Great Barrier Reef.
Credit: NASA
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If not for global warming, the crurotarsans may have been more dominant on Earth than the dinosaurs. Today, alligators and crocodiles are the only living relatives of this once-powerful group of reptiles.
Image Credit: Stephen Brusatte, Columbia University

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A photo of unpolished natural diamond. Credit: A. Sommer
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Using this humidity chamber, researchers detected the formation of crystal water layers on a hydrogenated diamond through a measured decrease in electrical conductivity in response to an increase in humidity. Credit: A. Sommer
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Late Carboniferous hydrocarbon-seep carbonates from the Dwyka Group (southern Namibia)
Credit: Tobias Himmler, University of Bremmen
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This image compares the air sac system of birds to what may have been used by dinosaurs.
Credit: NSF
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Aerosteon riocoloradensis was discovered during an expedition to Argentina in 1996.
Image Credit: Todd Marshall, courtesy of Project Exploration
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Amphimedon queenslandica

Credit: Bryony Fahey (University of Queensland)
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Researcher Loren Babcock, professor of earth sciences at Ohio State University. Credit: Kevin Fitzsimons, Ohio State University.
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The trackway of one of the earliest animals, a multilegged creature that walked over the bed of an ancient sea once covering Nevada. The animal left behind a pair of parallel impressions - small, round dots in the silt that later became rock. Credit: Kevin Fitzsimons, Ohio State University.
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Tree of life, divided between major cell types, those with a nucleus (Eukaryotes) and without a nucleus (Prokaryotes: the Bacteria and Archaea).
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The concept of horizontal gene transfer has been a driving force in evolution. All three domains have genetic material derived from other domains. Image Credit: Doolittle, 1999.
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Carl Woese defined the Archaea domain of life in 1977 by phylogenetic taxonomy of 16S ribosomal RNA. Woese also was the originator of the RNA world hypothesis, which says that early in the history of life RNA may have once performed functions that today are shared by DNA and proteins. Photo credit: University of Illinois at Urbana-Champaign.
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Archaea are simple cells that don´t have nucei. They resemble bacteria in their cell structure, but the genes of Archaea and several of their metabolic pathways are more closely related to those of Eukaryotes. Image credit: MIT.
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A Eukaryotic cell is an extremely complex system.
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A bacterial cell is not as complex as a eukaryotic cell, but it still has some very intricate systems and capabilities.

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