Rosalind Franklin: Great Minds. Dino 101 - Geologic Time Scale. History of life through time. How Many Species? A Study Says 8.7 Million, but It’s Tricky. Annotated version of Watson and Crick paper. Reprinted with permission from Nature magazine A Structure for Deoxyribose Nucleic Acid J. D. Watson and F. H. C. Crick (1) April 25, 1953 (2), Nature (3), 171, 737-738 We wish to suggest a structure for the salt of deoxyribose nucleic acid (D.N.A.). A structure for nucleic acid has already been proposed by Pauling (4) and Corey1. . (1) We believe that the material which gives the X-ray diagrams is the salt, not the free acid. . (2) Some of the van der Waals distances appear to be too small. Another three-chain structure has also been suggested by Fraser (in the press). The structure is an open one, and its water content is rather high.
The novel feature of the structure is the manner in which the two chains are held together by the purine and pyrimidine bases. If it is assumed that the bases only occur in the structure in the most plausible tautomeric forms (that is, with the keto rather than the enol configurations) it is found that only specific pairs of bases can bond together. Explore DNA | HHMI.org. Science/Nature | Oldest evidence of photosynthesis. Scientists claim to have found the oldest evidence of photosynthesis - the most important chemical reaction on Earth - in 3.7-billion-year-old rocks.
Photosynthesis is the process by which plants, algae and certain bacteria convert sunlight to chemical energy. Danish researchers say rocks from Greenland show life-forms were using the process about one billion years earlier than has previously been shown. Details of the research are published in Earth and Planetary Science Letters. Professor Minik Rosing and Professor Robert Frei, both of the University of Copenhagen, Denmark, analysed ancient seafloor sediments in Isua, Greenland, where they had previously found the earliest evidence of life on Earth.
"What this demonstrates is that the Earth had a functioning biosphere before 3.7 billion years ago," Professor Rosing told BBC News Online. Uranium signature But the high abundance of uranium relative to thorium in Isua rocks suggested that uranium had been chemically separated from thorium. "How I Wet Your Mother": Annie Awards | The Simpsons | Animation on FOX. Vent Biology. Forces of Change. Introduction to evolution and natural selection | Evolution and natural selection. Carbon Cycle @ National Geographic Magazine. Get a taste of what awaits you in print from this compelling excerpt. It's there on a monitor: the forest is breathing. Late summer sunlight filters through a canopy of green as Steven Wofsy unlocks a shed in a Massachusetts woodland and enters a room stuffed with equipment and tangled with wires and hoses. The machinery monitors the vital functions of a small section of Harvard Forest in the center of the state. Bright red numbers dance on a gauge, flickering up and down several times a second.
The reading reveals the carbon dioxide concentration just above the treetops near the shed, where instruments on a hundred-foot (30-meter) tower of steel lattice sniff the air. The numbers are running surprisingly low for the beginning of the 21st century: around 360 parts per million, ten less than the global average. In nourishing itself, this patch of pine, oak, and maple is also undoing a tiny bit of a great global change driven by humanity. By rights it should be worse. Who can complain? Phases of mitosis | Cell division. Photosynthesis | Photosynthesis. PlanetQuest - The Search for Another Earth. Tree of Life Web Project.
The Tree of Life Web Project (ToL) is a collaborative effort of biologists and nature enthusiasts from around the world. On more than 10,000 World Wide Web pages, the project provides information about biodiversity, the characteristics of different groups of organisms, and their evolutionary history (phylogeny). Each page contains information about a particular group, e.g., salamanders, segmented worms, phlox flowers, tyrannosaurs, euglenids, Heliconius butterflies, club fungi, or the vampire squid.
ToL pages are linked one to another hierarchically, in the form of the evolutionary tree of life. Starting with the root of all Life on Earth and moving out along diverging branches to individual species, the structure of the ToL project thus illustrates the genetic connections between all living things. The world's biomes. Online exhibits The world's biomes Biomes are defined as "the world's major communities, classified according to the predominant vegetation and characterized by adaptations of organisms to that particular environment" (Campbell 1996).
The importance of biomes cannot be overestimated. Biomes have changed and moved many times during the history of life on Earth. More recently, human activities have drastically altered these communities. Thus, conservation and preservation of biomes should be a major concern to all. Here we group biomes into six major types: Conservation and preservation of biomes Because we share the world with many other species of plants and animals, we must consider the consequences of our actions.
Forests are important as they are home to the most diverse biotic communties in the world. Logging has depleted many old-growth temperate forests. The freshwater and marine biomes are probably the most important of all the biomes. Biosphere2. Detectable civilizations in our galaxy 1 | Life in the Universe.