A hologram is an image that appears to be three dimensional and which can be seen with the naked eye. Holography is the practice of making holograms. A hologram is a photographic recording of a light field, rather than an image formed by a lens; the holographic medium, i.e. the object produced by a holographic process is unintelligible when viewed under diffuse ambient light. It is an encoding of the light field as an interference pattern of variations in the opacity, density, or surface profile of the photographic medium; when suitably lit, the interference pattern diffracts the light into an accurate reproduction of the original light field, the objects that were in it exhibit visual depth cues such as parallax and perspective that change realistically with the relative position of the observer. That is, the view of the image from different angles represents the subject viewed from similar angles. In its pure form, holography requires the use of laser light for illuminating the subject and for viewing the finished hologram.
A microscopic level of detail throughout the recorded scene can be reproduced. In common practice, major image quality compromises are made to eliminate the need for laser illumination to view the hologram, in some cases, to make it. Holographic portraiture resorts to a non-holographic intermediate imaging procedure, to avoid the hazardous high-powered pulsed lasers otherwise needed to optically "freeze" moving subjects as as the motion-intolerant holographic recording process requires. Holograms can now be computer-generated to show objects or scenes that never existed. Holography is distinct from lenticular and other earlier autostereoscopic 3D display technologies, which can produce superficially similar results but are based on conventional lens imaging. Images requiring the aid of special glasses or other intermediate optics, stage illusions such as Pepper's Ghost and other unusual, baffling, or magical images are incorrectly called holograms; the Hungarian-British physicist Dennis Gabor was awarded the Nobel Prize in Physics in 1971 "for his invention and development of the holographic method".
His work, done in the late 1940s, was built on pioneering work in the field of X-ray microscopy by other scientists including Mieczysław Wolfke in 1920 and William Lawrence Bragg in 1939. The discovery was an unexpected result of research into improving electron microscopes at the British Thomson-Houston Company in Rugby and the company filed a patent in December 1947; the technique as invented is still used in electron microscopy, where it is known as electron holography, but optical holography did not advance until the development of the laser in 1960. The word holography comes from the Greek words ὅλος and γραφή; the development of the laser enabled the first practical optical holograms that recorded 3D objects to be made in 1962 by Yuri Denisyuk in the Soviet Union and by Emmett Leith and Juris Upatnieks at the University of Michigan, USA. Early holograms used silver halide photographic emulsions as the recording medium, they were not efficient as the produced grating absorbed much of the incident light.
Various methods of converting the variation in transmission to a variation in refractive index were developed which enabled much more efficient holograms to be produced. Several types of holograms can be made. Transmission holograms, such as those produced by Leith and Upatnieks, are viewed by shining laser light through them and looking at the reconstructed image from the side of the hologram opposite the source. A refinement, the "rainbow transmission" hologram, allows more convenient illumination by white light rather than by lasers. Rainbow holograms are used for security and authentication, for example, on credit cards and product packaging. Another kind of common hologram, the reflection or Denisyuk hologram, can be viewed using a white-light illumination source on the same side of the hologram as the viewer and is the type of hologram seen in holographic displays, they are capable of multicolour-image reproduction. Specular holography is a related technique for making three-dimensional images by controlling the motion of specularities on a two-dimensional surface.
It works by reflectively or refractively manipulating bundles of light rays, whereas Gabor-style holography works by diffractively reconstructing wavefronts. Most holograms produced are of static objects but systems for displaying changing scenes on a holographic volumetric display are now being developed. Holograms can be used to store and process information optically. In its early days, holography required high-power expensive lasers, but nowadays, mass-produced low-cost semi-conductor or diode lasers, such as those found in millions of DVD recorders and used in other common applications, can be used to make holograms and have made holography much more accessible to low-budget researchers and dedicated hobbyists, it was thought that it would be possible to use X-rays to make holograms of small objects and view them using visible light. Today, holograms with x-rays are generated by using synchrotrons or x-ray free-electron lasers as radiation sources and pixelated detectors such as CCDs as recording medium.
The reconstruction is retrieved via computation. Due to the shorter wavelength of x-rays compared to visible light, this approach allows imaging objects with higher spatial resolution; as free-electron lasers can provide ultrashort and x-ray pulses in the range of femtoseconds which are intense and coherent, x-ray holography
Las Vegas Valley
The Las Vegas Valley is a major metropolitan area in the southern part of the U. S. state of Nevada. The state's largest urban agglomeration, it is the heart of the Las Vegas–Paradise-Henderson, NV MSA; the Valley is defined by the Las Vegas Valley landform, a 600 sq mi basin area surrounded by mountains to the north, south and west of the metropolitan area. The Valley is home to the three largest incorporated cities in Nevada: Las Vegas and North Las Vegas. Five unincorporated towns governed by the Clark County government are part of the Las Vegas Township and constitute the largest community in the state of Nevada; the names Las Vegas and Vegas are interchangeably used to indicate the Valley, the Strip, the city, as a brand by the Las Vegas Convention and Visitors Authority to denominate the region. The Valley is affectionately known as the "ninth island" by Hawaii natives and Las Vegans alike, in part due to the large number of people from Hawaii who live in and travel to Las Vegas. Since the 1990s the Las Vegas Valley has seen rapid growth, tripling its population of 741,459 in 1990 to 2,227,053 estimated in 2018.
The Las Vegas Valley remains one of the fastest growing metropolitan areas in the United States, in its short history has established a diverse presence in international business, urban development and entertainment, as well as one of the most iconic and most visited tourist destinations in the world. In 2014, a record breaking 41 million visited the Las Vegas area, producing a gross metropolitan product of more than $100 billion; the first reported non-Native American visitor to the Las Vegas Valley was the Mexican scout Rafael Rivera in 1829. Las Vegas was named by Mexicans in the Antonio Armijo party, including Rivera, who used the water in the area while heading north and west along the Old Spanish Trail from Texas. In the 19th century, areas of the valley contained artesian wells that supported extensive green areas, or meadows, hence the name Las Vegas; the area was settled by Mormon farmers in 1854 and became the site of a United States Army fort in 1864, beginning a long relationship between southern Nevada and the U.
S. military. Since the 1930s, Las Vegas has been identified as a gaming center as well as a resort destination targeting adults. Nellis Air Force Base is located in the northeast corner of the valley; the ranges that the Nellis pilots use and various other land areas used by various federal agencies, limit growth of the valley in terms of geographic area. Businessman Howard Hughes arrived in the late 1960s and purchased many casino hotels, as well as television and radio stations in the area. Legitimate corporations began to purchase casino hotels as well, the mob was run out by the federal government over the next several years; the constant stream of tourist dollars from the hotels and casinos was augmented by a new source of federal money from the establishment of what is now Nellis Air Force Base. The influx of military personnel and casino job-hunters helped start a land building boom, now leveling off; the Las Vegas area remains one of the world's top entertainment destinations. The valley is contained in the Las Vegas Valley landform.
This includes the cities of Las Vegas, North Las Vegas, Henderson, the unincorporated towns of Summerlin South, Spring Valley, Sunrise Manor, Enterprise and Whitney. The valley is technically located within the larger metropolitan area, as the metropolitan area covers all of Clark County including parts that do not fall within the valley; the government of Clark County has an "Urban Planning Area" of Las Vegas. This definition is a rectangular area, about 20 mi from east to west and 30 miles from north to south. Notable exclusions from the "Urban Planning Area" include Red Rock, Blue Diamond, Mount Charleston; the Las Vegas Metropolitan Police Department is the largest police department in the valley and the state and exercises jurisdiction in the entire county. There are 3,000 police officers that cover the city of Las Vegas; the department does not exercise primary jurisdiction in areas with separate police forces such as North Las Vegas, Boulder City, Nellis Air Force Base and the Paiute reservation.
The Las Vegas Valley lies in the Mojave Desert. The surrounding land is desert with mountains in the distance; the Las Vegas Valley lies in a high-altitude portion of the Mojave Desert, with a subtropical hot-desert climate. The Valley averages less than 5 in of rain annually. Daily daytime summer temperatures in July and August range from 100 °F to 110 °F, while nights range from 72 °F to 80 °F. Low humidity, tempers the effect of these temperatures, though dehydration, heat exhaustion, sun stroke can occur after a limited time outdoors in the summer; the interiors of automobiles prove deadly to small children and pets during the summer and surfaces exposed to the sun can cause first- and second-degree burns to unprotected skin. July and August can be marked by "monsoon season", when moist winds from the Gulf of California soak much of the Southwestern United States. While not only raising humidity levels, these winds develop into dramatic desert thunderstorms that can sometimes cause flash flooding.
Winters in the Las Vegas Valley are chilly, but sunny. Winter highs in December and January range from 52 °F to 60 °F, while nighttime lows range from 34 °F to 42 °F (
G. P. Putnam's Sons
G. P. Putnam's Sons is an American book publisher based in New York. Since 1996, it has been an imprint of the Penguin Group; the company began as Wiley & Putnam with the 1838 partnership between George Palmer Putnam and John Wiley, whose father had founded his own company in 1807. In 1841, Putnam went to London where he set up a branch office, the first American company to do so. In 1848, he returned to New York, where he dissolved the partnership with John Wiley and established G. Putnam Broadway, publishing a variety of works including quality illustrated books. Wiley began John Wiley, still an independent publisher to the present day. In 1853, G. P. Putnam & Co. started Putnam’s Magazine with Charles Frederick Briggs as its editor. On George Palmer Putnam’s death in 1872, his sons George H. John and Irving inherited the business and the firm's name was changed to G. P. Putnam's Sons. Son George H. Putnam became president of a position he held for the next fifty-two years. In 1874, the company established its own book printing and manufacturing office, set up by John Putnam and operating out of newly leased premises at 182 Fifth Avenue.
This printing side of the business became a separate division called the Knickerbocker Press, was relocated in 1889 to the Knickerbocker Press Building, built for the press in New Rochelle, New York. On the death of George H. Putnam in 1930, the various Putnam heirs voted to merge the firm with Minton, Balch & Co. who became the majority stockholders. George Palmer Putnam's grandson, George P. Putnam, left the firm at that time. Melville Minton, the partner and sales manager of Minton Balch & Co. became acting president and majority stockholder of the firm until his death in 1956. In 1936, Putnam acquired the publisher Coward-McCann, ran it as an imprint into the 1980s. Upon Melville Minton's death, his son Walter J. Minton took control of the company. In 1965, G. P. Putnam's Sons acquired a mass market paperback publishing house. MCA bought Putnam Publishing Group and Berkley Publishing Group in 1975. Phyllis E. Grann, running Pocket Books for Simon & Schuster was brought on board in 1976 as editor-in-chief.
Grann worked with MCA executive Stanley Newman on a financial model to make Putnam profitable. This model emphasized publishing key authors annually and took Putnam from $10 million in revenue to over $100 million by 1983. While keeping the list at 75 titles a year, Putnam focused on winners like Tom Clancy whose book Red Storm Rising sold nearly a million copies in 1986. Putnam along with other publishers in the 1980s moved to a heavy discount hardcover model to keep up with demand and sales through bookstore chains and price clubs. Phyllis Grann was promoted to CEO of Putnam in 1987 becoming the first woman to be CEO of a major publishing house. By 1993, the publisher was making $200 million in revenue. In 1982, Putnam acquired Grosset & Dunlap from Filmways. In 1982, Putnam acquired the book publishing division of Playboy Enterprises, which included Seaview Books. In the 1990s ownership of Putnam changed a number of times. MCA was bought by Matsushita Electric in 1990; the Seagram Company acquired 80% of MCA from Matsushita and shortly thereafter Seagram changed the name of the company to Universal Studios, Inc.
The new owners had no interest in publishing, but Phyllis Grann stepped in and was able to broker the deal for Putnam to be merged with Penguin Group in 1996, a division of British publishing conglomerate, Pearson PLC Putnam and the Penguin Group formed Penguin Putnam Inc. In 2001, Grann abruptly left after speculation over tensions with Pearson CEO Marjorie Scardino. In 2013, Penguin merged with Bertelsmann's Random House. Books in the United States About Putnam at Penguin Group
The Māori are the indigenous Polynesian people of New Zealand. Māori originated with settlers from eastern Polynesia, who arrived in New Zealand in several waves of canoe voyages some time between 1250 and 1300. Over several centuries in isolation, the Polynesian settlers developed a unique culture, with their own language, a rich mythology, distinctive crafts and performing arts. Early Māori formed tribal groups based on organisation. Horticulture flourished using plants; the arrival of Europeans to New Zealand, starting in the 17th century, brought enormous changes to the Māori way of life. Māori people adopted many aspects of Western society and culture. Initial relations between Māori and Europeans were amicable, with the signing of the Treaty of Waitangi in 1840, the two cultures coexisted as part of a new British colony. Rising tensions over disputed land sales led to conflict in the 1860s. Social upheaval, decades of conflict and epidemics of introduced disease took a devastating toll on the Māori population, which fell dramatically.
By the start of the 20th century, the Māori population had begun to recover, efforts have been made to increase their standing in wider New Zealand society and achieve social justice. Traditional Māori culture has thereby enjoyed a significant revival, further bolstered by a Māori protest movement that emerged in the 1960s. In the 2013 census, there were 600,000 people in New Zealand identifying as Māori, making up 15 percent of the national population, they are the second-largest ethnic group in New Zealand, after European New Zealanders. In addition, more than 140,000 Māori live in Australia; the Māori language is spoken to some extent by about a fifth of all Māori, representing 3 per cent of the total population. Māori are active in all spheres of New Zealand culture and society, with independent representation in areas such as media and sport. Disproportionate numbers of Māori face significant economic and social obstacles, have lower life expectancies and incomes compared with other New Zealand ethnic groups.
They suffer higher levels of crime, health problems, educational under-achievement. A number of socioeconomic initiatives have been instigated with the aim of "closing the gap" between Māori and other New Zealanders. Political and economic redress for historical grievances is ongoing. In the Māori language, the word māori means "normal", "natural" or "ordinary". In legends and oral traditions, the word distinguished ordinary mortal human beings—tāngata māori—from deities and spirits. Wai māori denotes "fresh water", as opposed to salt water. There are cognate words in most Polynesian languages, all deriving from Proto-Polynesian *maqoli, which has the reconstructed meaning "true, genuine"; the spelling of "Māori" with or without the macron is inconsistent in general-interest English-language media in New Zealand, although some newspapers and websites have adopted the standard Māori-language spelling. Early visitors from Europe to New Zealand referred to the indigenous inhabitants as "New Zealanders" or as "natives".
The Māori used the term Māori to describe themselves in a pan-tribal sense. Māori people use the term tangata whenua to identify in a way that expresses their relationship with a particular area of land; the term can refer to the Māori people as a whole in relation to New Zealand as a whole. The Māori Purposes Act of 1947 required the use of the term "Māori" rather than "Native" in official usage; the Department of Native Affairs was renamed as the Department of Māori Affairs. Before 1974, the government required documented ancestry to determine the legal definition of "a Māori person". For example, bloodlines or percentage of Māori ancestry was used to determine whether a person should enroll on the general electoral roll or the separate Māori roll. In 1947, the authorities determined that a man, five-eighths Māori had improperly voted in the general parliamentary electorate of Raglan; the Māori Affairs Amendment Act 1974 changed the definition, allowing individuals to self-identify as to their cultural identity.
In matters involving financial benefits provided by the government to people of Māori ethnicity—scholarships, for example, or Waitangi Tribunal settlements—authorities require some documentation of ancestry or continuing cultural connection but no minimum "blood" requirement exists as determined by the government. The most current reliable evidence indicates that the initial settlement of New Zealand occurred around 1280 CE, at the end of the medieval warm period. Previous dating of some kiore bones at 50–150 has now been shown to have been unreliable. Māori oral history describes the arrival of ancestors from Hawaiki, in large ocean-going waka. Migration accounts vary among tribes, whose members may identify with several waka in their genealogies. In the last few decades, mitochondrial-DNA research has allowed an estimate to be made of the number of women in the founding population—between 50 and 100. Evidence fro
Open Library is an online project intended to create "one web page for every book published". Created by Aaron Swartz, Brewster Kahle, Alexis Rossi, Anand Chitipothu, Rebecca Malamud, Open Library is a project of the Internet Archive, a nonprofit organization, it has been funded in part by grants from the California State Library and the Kahle/Austin Foundation. Open Library provides online access to many public out-of-print books, its book information is collected from the Library of Congress, other libraries, Amazon.com, as well as from user contributions through a Wiki-like interface. If books are available in digital form, a button labelled "Read" appears next to its catalog listing. Links to where books can be purchased or borrowed are provided. There are different entities in the database: authors works editions Open Library claims to have 6 million authors and 20 million books, about one million public domain books available as digitized books. Tens of thousands of modern books were made available from four and 150 libraries and publishers for ebook digital lending.
Other books including in-print and in-copyright books have been scanned from copies in library collections, library discards, donations, are being distributed in digital form. Open Library began in 2006 with Aaron Swartz as the original engineer and leader of Open the Library's technical team; the project was led by George Oates from April 2009 to December 2011. Oates was responsible for a complete site redesign during her tenure. In 2015, the project was continued by Giovanni Damiola and Brenton Cheng and Mek Karpeles in 2016; the site was redesigned and relaunched in May 2010. Its codebase is on GitHub; the site uses Infobase, its own database framework based on PostgreSQL, Infogami, its own Wiki engine written in Python. The source code to the site is published under the GNU Affero General Public License; the website was relaunched adding ADA compliance and offering over 1 million modern and older books to the print disabled in May 2010 using the DAISY Digital Talking Book. Under certain provisions of United States copyright law, libraries are sometimes able to reproduce copyrighted works in formats accessible to users with disabilities.
As of February 2019, the Open Library has been accused of mass copyright violation, via the systematic distribution of in-print, in-copyright books, by the American Authors Guild, the British Society of Authors, the Australian Society of Authors, the Science Fiction and Fantasy Writers of America, the US National Writers Union, a coalition of 37 national and international organizations of "writers, translators and graphic artists. The UK Society of Authors threatened legal action unless the Open Library agreed to cease distribution of copyrighted works by 1-Feb-2019. Individual authors reported that Open Library had ignored multiple DMCA takedown notices until after they made a fuss on the Internet Archive blog Free Software licensing Google Books LibraryThing List of AGPL web applications List of digital library projects Online Computer Library Center – creator of WorldCat Online Public Access Catalog Meadows, Chris. "The Internet Archive's OpenLibrary project violates copyright, the Authors Guild warns".
TeleRead. Official website The Open Library public domain audiobook at LibriVox [
Robert A. Heinlein
Robert Anson Heinlein was an American science-fiction author, aeronautical engineer, retired Naval officer. Called the "dean of science fiction writers", He was among the first to emphasize scientific accuracy in his fiction, was thus a pioneer of the subgenre of hard science fiction, his work continues to have an influence on the science-fiction genre, on modern culture more generally. Heinlein became one of the first American science-fiction writers to break into mainstream magazines such as The Saturday Evening Post in the late 1940s, he was one of the best-selling science-fiction novelists for many decades, he, Isaac Asimov, Arthur C. Clarke are considered the "Big Three" of English-language science fiction authors. Notable Heinlein works include Stranger in a Strange Land, Starship Troopers and The Moon Is a Harsh Mistress, his work sometimes had controversial aspects, such as plural marriage in The Moon is a Harsh Mistress, militarism in Starship Troopers and technologically competent women characters that were strong and independent, yet stereotypically feminine – such as Friday.
A writer of numerous science-fiction short stories, Heinlein was one of a group of writers who came to prominence under the editorship of John W. Campbell at Astounding Science Fiction magazine, though Heinlein denied that Campbell influenced his writing to any great degree. Within the framework of his science-fiction stories, Heinlein addressed certain social themes: the importance of individual liberty and self-reliance, the obligation individuals owe to their societies, the influence of organized religion on culture and government, the tendency of society to repress nonconformist thought, he speculated on the influence of space travel on human cultural practices. Heinlein was named the first Science Fiction Writers Grand Master in 1974. Four of his novels won Hugo Awards. In addition, fifty years after publication, seven of his works were awarded "Retro Hugos"—awards given retrospectively for works that were published before the Hugo Awards came into existence. In his fiction, Heinlein coined terms that have become part of the English language, including "grok", "waldo", "speculative fiction", as well as popularizing existing terms like "TANSTAAFL", "pay it forward", "space marine".
He anticipated mechanical computer-aided design with "Drafting Dan" and described a modern version of a waterbed in his novel Beyond This Horizon, though he never patented nor built one. In the first chapter of the novel Space Cadet he anticipated the cell-phone, 35 years before Motorola invented the technology. Several of Heinlein's works have been adapted for television. Heinlein was born on July 7, 1907 in Butler, Missouri, he was a 6th-generation German-American: a family tradition had it that Heinleins fought in every American war starting with the War of Independence. His childhood was spent in Missouri; the outlook and values of this time and place had a definite influence on his fiction his works, as he drew upon his childhood in establishing the setting and cultural atmosphere in works like Time Enough for Love and To Sail Beyond the Sunset. Heinlein's experience in the U. S. Navy exerted a strong influence on his writing, he graduated from the U. S. Naval Academy in Annapolis, with the class of 1929.
Shortly after graduation, he was commissioned as an ensign by the U. S. Navy, he advanced to lieutenant, junior grade while serving aboard the new aircraft carrier USS Lexington in 1931, where he worked in radio communications in its earlier phases, with the carrier's aircraft. The captain of this carrier was Ernest J. King, who served as the Chief of Naval Operations and Commander-in-Chief, U. S. Fleet during World War II. Heinlein was interviewed during his years by military historians who asked him about Captain King and his service as the commander of the U. S. Navy's first modern aircraft carrier. Heinlein served as gunnery officer aboard the destroyer USS Roper in 1933 and 1934, reaching the rank of lieutenant, his brother, Lawrence Heinlein, served in the U. S. Army, the U. S. Air Force, the Missouri National Guard, reaching the rank of major general in the National Guard. In 1929, Heinlein married Elinor Curry of Kansas City. However, their marriage only lasted about a year, his second marriage in 1932 to Leslyn MacDonald lasted for 15 years.
MacDonald was, according to the testimony of Heinlein's Navy friend, Rear Admiral Cal Laning, "astonishingly intelligent read, liberal, though a registered Republican," while Isaac Asimov recalled that Heinlein was, at the time, "a flaming liberal". At the Philadelphia Naval Shipyard Heinlein met and befriended a chemical engineer named Virginia "Ginny" Gerstenfeld. After the war, her engagement having fallen through, she moved to UCLA for doctoral studies in chemistry and made contact again; as his second wife's alcoholism spun out of control, Heinlein moved out and the couple filed for divorce. Heinlein's friendship with Virginia turned into a relationship and on October 21, 1948 — shortly after the decree nisi came through — they married in the town of Raton, New Mexico, shortly after setting up housekeeping in Colorado, they remained married until Heinlein's death. As Heinlein's increasing success as a writer resolved their initial financial woes, they had a house custom built with various innovative features described in an article in Popular Mechanics.
In 1965, after various chronic health problems of
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System after Mercury. In English, Mars carries a name of the Roman god of war, is referred to as the "Red Planet" because the reddish iron oxide prevalent on its surface gives it a reddish appearance, distinctive among the astronomical bodies visible to the naked eye. Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys and polar ice caps of Earth; the days and seasons are comparable to those of Earth, because the rotational period as well as the tilt of the rotational axis relative to the ecliptic plane are similar. Mars is the site of Olympus Mons, the largest volcano and second-highest known mountain in the Solar System, of Valles Marineris, one of the largest canyons in the Solar System; the smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature. Mars has two moons and Deimos, which are small and irregularly shaped.
These may be captured asteroids, similar to a Mars trojan. There are ongoing investigations assessing the past habitability potential of Mars, as well as the possibility of extant life. Future astrobiology missions are planned, including the Mars 2020 and ExoMars rovers. Liquid water cannot exist on the surface of Mars due to low atmospheric pressure, less than 1% of the Earth's, except at the lowest elevations for short periods; the two polar ice caps appear to be made of water. The volume of water ice in the south polar ice cap, if melted, would be sufficient to cover the entire planetary surface to a depth of 11 meters. In November 2016, NASA reported finding a large amount of underground ice in the Utopia Planitia region of Mars; the volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior. Mars can be seen from Earth with the naked eye, as can its reddish coloring, its apparent magnitude reaches −2.94, surpassed only by Jupiter, the Moon, the Sun.
Optical ground-based telescopes are limited to resolving features about 300 kilometers across when Earth and Mars are closest because of Earth's atmosphere. Mars is half the diameter of Earth with a surface area only less than the total area of Earth's dry land. Mars is less dense than Earth, having about 15% of Earth's volume and 11% of Earth's mass, resulting in about 38% of Earth's surface gravity; the red-orange appearance of the Martian surface is caused by rust. It can look like butterscotch. Like Earth, Mars has differentiated into a dense metallic core overlaid by less dense materials. Current models of its interior imply a core with a radius of about 1,794 ± 65 kilometers, consisting of iron and nickel with about 16–17% sulfur; this iron sulfide core is thought to be twice as rich in lighter elements as Earth's. The core is surrounded by a silicate mantle that formed many of the tectonic and volcanic features on the planet, but it appears to be dormant. Besides silicon and oxygen, the most abundant elements in the Martian crust are iron, aluminum and potassium.
The average thickness of the planet's crust is about 50 km, with a maximum thickness of 125 km. Earth's crust averages 40 km. Mars is a terrestrial planet that consists of minerals containing silicon and oxygen and other elements that make up rock; the surface of Mars is composed of tholeiitic basalt, although parts are more silica-rich than typical basalt and may be similar to andesitic rocks on Earth or silica glass. Regions of low albedo suggest concentrations of plagioclase feldspar, with northern low albedo regions displaying higher than normal concentrations of sheet silicates and high-silicon glass. Parts of the southern highlands include detectable amounts of high-calcium pyroxenes. Localized concentrations of hematite and olivine have been found. Much of the surface is covered by finely grained iron oxide dust. Although Mars has no evidence of a structured global magnetic field, observations show that parts of the planet's crust have been magnetized, suggesting that alternating polarity reversals of its dipole field have occurred in the past.
This paleomagnetism of magnetically susceptible minerals is similar to the alternating bands found on Earth's ocean floors. One theory, published in 1999 and re-examined in October 2005, is that these bands suggest plate tectonic activity on Mars four billion years ago, before the planetary dynamo ceased to function and the planet's magnetic field faded, it is thought that, during the Solar System's formation, Mars was created as the result of a stochastic process of run-away accretion of material from the protoplanetary disk that orbited the Sun. Mars has many distinctive chemical features caused by its position in the Solar System. Elements with comparatively low boiling points, such as chlorine and sulphur, are much more common on Mars than Earth. After the formation of the planets, all were subjected to the so-called "Late Heavy Bombardment". About 60% of the surface of Mars shows a record of impacts from that era, whereas much of the remaining surface is underlain by immense impact basins caused by those events.
There is evidence of an enormous impact basin in the northern hemisphere of Mars, spanning 10,600 by 8,500 km, or four times the size of the Moon's South Pole – Aitk