The Jurassic is a geologic period and stratigraphic system that spanned from the end of the Triassic Period 201.4 million years ago (Mya) to the beginning of the Cretaceous Period, approximately 145 Mya. The Jurassic constitutes the middle period of the Mesozoic Era and is named after the Jura Mountains, where limestone strata from the period were first identified.
The Triassic–Jurassic (Tr-J) extinction event (TJME), often called the end-Triassic extinction, was a Mesozoic extinction event that marks the boundary between the Triassic and Jurassic periods, 201.4 million years ago, and is one of the top five major extinction events of the Phanerozoic eon, profoundly affecting life on land and in the oceans. In the seas, the entire class of conodonts and 23–34% of marine genera disappeared. On land, all archosauromorphs other than crocodylomorphs, pterosaurs, and dinosaurs became extinct; some of the groups which died out were previously abundant, such as aetosaurs, phytosaurs, and rauisuchids. Some remaining non-mammalian therapsids and many of the large temnospondyl amphibians had become extinct prior to the Jurassic as well. However, there is still much uncertainty regarding a connection between the Tr-J boundary and terrestrial vertebrates, due to a lack of terrestrial fossils from the Rhaetian (latest) stage of the Triassic. What was left fairly untouched were plants, crocodylomorphs, dinosaurs, pterosaurs and mammals; this allowed the dinosaurs, pterosaurs, and crocodylomorphs to become the dominant land animals for the next 135 million years.
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from soil by restricting the former term specifically to displaced soil.
A diatom is any member of a large group comprising several genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of the Earth's biomass: they generate about 20 to 50 percent of the oxygen produced on the planet each year, take in over 6.7 billion tonnes of silicon each year from the waters in which they live, and constitute nearly half of the organic material found in the oceans. The shells of dead diatoms can reach as much as a half-mile deep on the ocean floor, and the entire Amazon basin is fertilized annually by 27 million tons of diatom shell dust transported by transatlantic winds from the African Sahara, much of it from the Bodélé Depression, which was once made up of a system of fresh-water lakes.
This is a timeline of quantum computing.
A scanning transmission electron microscope (STEM) is a type of transmission electron microscope (TEM). Pronunciation is [stɛm] or [ɛsti:i:ɛm]. As with a conventional transmission electron microscope (CTEM), images are formed by electrons passing through a sufficiently thin specimen. However, unlike CTEM, in STEM the electron beam is focused to a fine spot which is then scanned over the sample in a raster illumination system constructed so that the sample is illuminated at each point with the beam parallel to the optical axis. The rastering of the beam across the sample makes STEM suitable for analytical techniques such as Z-contrast annular dark-field imaging, and spectroscopic mapping by energy dispersive X-ray (EDX) spectroscopy, or electron energy loss spectroscopy (EELS). These signals can be obtained simultaneously, allowing direct correlation of images and spectroscopic data.
In human mitochondrial genetics, Haplogroup D is a human mitochondrial DNA (mtDNA) haplogroup. It is a descendant haplogroup of haplogroup M, thought to have arisen somewhere in East Asia, between roughly 60,000 and 35,000 years ago.
The environmental impacts of animal agriculture vary because of the wide variety of agricultural practices employed around the world. Despite this, all agricultural practices have been found to have a variety of effects on the environment to some extent. Animal agriculture, in particular meat production, can cause pollution, greenhouse gas emissions, biodiversity loss, disease, and significant consumption of land, food, and water. Meat is obtained through a variety of methods, including organic farming, free-range farming, intensive livestock production, and subsistence agriculture. The livestock sector also includes wool, egg and dairy production, the livestock used for tillage, and fish farming.
In biology, abiogenesis or the origin of life is the natural process by which life has arisen from non-living matter, such as simple organic compounds. The prevailing scientific hypothesis is that the transition from non-living to living entities on Earth was not a single event, but a process of increasing complexity involving the formation of a habitable planet, the prebiotic synthesis of organic molecules, molecular self-replication, self-assembly, autocatalysis, and the emergence of cell membranes. The transition from non-life to life has never been observed experimentally, but many proposals have been made for different stages of the process.
Lampreys are a group of jawless fish comprising the order Petromyzontiformes. The adult lamprey is characterized by a toothed, funnel-like sucking mouth. The common name "lamprey" is probably derived from Latin lampetra, which may mean "stone licker", though the etymology is uncertain. Lamprey is sometimes seen for the plural form.
An electrocatalyst is a catalyst that participates in electrochemical reactions. Electrocatalysts are a specific form of catalysts that function at electrode surfaces or, most commonly, may be the electrode surface itself. An electrocatalyst can be heterogeneous such as a platinized electrode. Homogeneous electrocatalysts, which are soluble, assist in transferring electrons between the electrode and reactants, and/or facilitate an intermediate chemical transformation described by an overall half reaction. Major challenges in electrocatalysts focus on fuel cells.
An atomic clock is a clock that measures time by monitoring the resonant frequency of atoms. It is based on atoms having different energy levels. Electron states in an atom are associated with different energy levels, and in transitions between such states they interact with a very specific frequency of electromagnetic radiation. This phenomenon serves as the basis for the International System of Units' (SI) definition of a second:
The second, symbol s, is the SI unit of time. It is defined by taking the fixed numerical value of the caesium frequency, , the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be 9192631770 when expressed in the unit Hz, which is equal to s−1.
Marine primary production is the chemical synthesis in the ocean of organic compounds from atmospheric or dissolved carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through chemosynthesis, which uses the oxidation or reduction of inorganic chemical compounds as its source of energy. Almost all life on Earth relies directly or indirectly on primary production. The organisms responsible for primary production are called primary producers or autotrophs.
The plant microbiome, also known as the phytomicrobiome, plays roles in plant health and productivity and has received significant attention in recent years. The microbiome has been defined as "a characteristic microbial community occupying a reasonably well-defined habitat which has distinct physio-chemical properties. The term thus not only refers to the microorganisms involved but also encompasses their theatre of activity".
The Camille Dreyfus Teacher-Scholar Awards are awards given to early-career researchers in chemistry by The Camille and Henry Dreyfus Foundation, Inc. "to support the research and teaching careers of talented young faculty in the chemical sciences." The Dreyfus Teacher-Scholar program began in 1970. In 1994, the program was divided into two parallel awards: The Camille Dreyfus Teacher-Scholar Awards Program, aimed at research universities, and the Henry Dreyfus Teacher-Scholar Awards Program, directed at primarily undergraduate institutions. This list compiles all the pre-1994 Teacher-Scholars, and the subsequent Camille Dreyfus Teacher-Scholars.
