历史地理学方面的英语介绍

历史地理学方面的英语介绍
历史地理学方面的英语介绍

历史地理学方面的英语介绍
Historical Geology
Historical geology focuses on the study of the evolution of earth and its life through time. Historical geology includes many subfields. Stratigraphy and sedimentary geology are fields that investigate layered rocks and the environments in which they are found. Geochronology is the study of determining the age of rocks, while paleontology is the study of fossils. Other fields, such as paleoceanography, paleoseismology, paleoclimatology, and paleomagnetism, apply geologic knowledge of ancient conditions to learn more about the earth. The Greek prefix paleo is used to identify ancient conditions or periods in time, and commonly means “the reconstruction of the past.”
B1 Stratigraphy
Stratigraphy is the study of the history of the earth's crust, particularly its stratified (layered) rocks. Stratigraphy is concerned with determining age relationships of rocks as well as their distribution in space and time. Rocks may be studied in an outcrop but commonly are studied from drilled cores (samples that have been collected by drilling into the earth). Most of the earth's surface is covered with sediment or layered rocks that record much of geologic history; this is what makes stratigraphy important. It is also important for many economic and environmental reasons. A large portion of the world's fossil fuels, such as oil, gas, and coal, are found in stratified rocks, and much of the world's groundwater is stored in sediments or stratified rocks.
Stratigraphy may be subdivided into a number of fields. Biostratigraphy is the use of fossils for age determination and correlation of rock layers; magnetostratigraphy is the use of magnetic properties in rocks for similar purposes. Newer fields in stratigraphy include chemostratigraphy, seismic stratigraphy, and sequence stratigraphy. Chemostratigraphy uses chemical properties of strata for age determination and correlation as well as for recognizing events in the geologic record. For example, oxygen isotopes (forms of oxygen that contain a different number of neutrons in the nuclei of atoms) may provide evidence of an ancient paleoclimate. Carbon isotopes may identify biologic events, such as extinctions. Rare chemical elements may be concentrated in a marker layer (a distinctive layer that can be correlated over long distances). Seismic stratigraphy is the subsurface study of stratified rocks using seismic reflection techniques. This field has revolutionized stratigraphic studies since the late 1970s and is now used extensively both on land and offshore. Seismic stratigraphy is used for economic reasons, such as finding oil, and for scientific studies. An offshoot of seismic stratigraphy is sequence stratigraphy, which helps geologists reconstruct sea level changes throughout time. The rocks used in sequence stratigraphy are bounded by, or surrounded by, surfaces of erosion called unconformities.
B2 Sedimentology
Sedimentology, or sedimentary geology, is the study of sediments and sedimentary rocks and the determination of their origin. Sedimentary geology is process oriented, focusing on how sediment was deposited. Sedimentologists are geologists who attempt to interpret past environments based on the observed characteristics, called facies, of sedimentary rocks. Facies analysis uses physical, chemical, and biological characteristics to reconstruct ancient environments. Facies analysis helps sedimentologists determine the features of the layers, such as their geometry, or layer shape; porosity, or how many pores the rocks in the layers have; and permeability, or how permeable the layers are to fluids. This type of analysis is important economically for understanding oil and gas reservoirs as well as groundwater supplies.
B3 Geochronology
The determination of the age of rocks is called geochronology. The fundamental tool of geochronology is radiometric dating (the use of radioactive decay processes as recorded in earth materials to determine the numerical age of rocks). Most radiometric dating techniques are useful in dating igneous and metamorphic rocks and minerals. One type of non-radiometric dating, called strontium isotope dating, measures different forms of the element strontium in sedimentary materials to date the layers. Geologists also have ways to determine the ages of surfaces that have been exposed to the sun and to cosmic rays. These methods are called thermoluminescence dating and cosmogenic isotope dating. Geologists can count the annual layers recorded in tree rings, ice cores, and certain sediments such as those found in lakes, for very precise geochronology. However, this method is only useful for time periods up to tens of thousands of years. Some geoscientists are now using Milankovitch cycles (the record of change in materials caused by variations in the earth's orbit) as a geologic time clock. See also Dating Methods: Radiometric Dating.
B4 Paleontology and Paleobiology
Paleontology is the study of ancient or fossil life. Paleobiology is the application of biological principles to the study of ancient life on earth. These fields are fundamental to stratigraphy and are used to reconstruct the history of organisms' evolution and extinction throughout earth history. The oldest fossils are older than 3 billion years, although fossils do not become abundant and diverse until about 500 million years ago. Different fossil organisms are characteristic of different times, and at certain times in earth history, there have been mass extinctions (times when a large proportion of life disappears). Other organisms then replace the extinct forms. The study of fossils is one of the most useful tools for reconstructing geologic history because plants and animals are sensitive to environmental changes, such as changes in the climate, temperature, food sources, or sunlight. Their fossil record reflects the world that existed while they were alive. Paleontology is commonly divided into vertebrate paleontology (the study of organisms with backbones), invertebrate paleontology (the study of organisms without backbones), and micropaleontology (the study of microscopic fossil organisms). Many other subfields of paleontology exist as well. Paleobotanists study fossil plants, and palynologists study fossil pollen. Ichnology is the study of trace fossils—tracks, trails, and burrows left by organisms. Paleoecology attempts to reconstruct the behavior and relationships of ancient organisms.
B5 Paleoceanography and Paleoclimatology
Paleoceanography (the study of ancient oceans) and paleoclimatology (the study of ancient climates) are two subfields that use fossils to help reconstruct ancient conditions. Scientists also study stable isotopes, or different forms, of oxygen to reconstruct ancient temperatures. They use carbon and other chemicals to reconstruct aspects of ancient oceanographic and climatic conditions. Detailed paleoclimatic studies have used cores from ice sheets in Antarctica and Greenland to reconstruct the last 200,000 years. Ocean cores, tree rings, and lake sediments are also useful in paleoclimatology. Geologists hope that by understanding past oceanographic and climatic changes, they can help predict future change.
VI HISTORY OF GEOLOGY
Geology originated as a modern scientific discipline in the 18th century, but humans have been collecting systematic knowledge of the earth since at least the Stone Age. In the Stone Age, people made stone tools and pottery, and had to know which materials were useful for these tasks. Between the 4th century and 1st century bc, ancient Greek and Roman philosophers began the task of keeping written records relating to geology. Throughout the medieval and Renaissance periods, people began to study mineralogy and made detailed geologic observations. The 18th and 19th centuries brought widespread study of geology, including the publication of Charles Lyell’s book Principles of Geology, and the National Surveys (expeditions that focused on the collection of geologic and other scientific data). The concept of geologic time was further developed during the 19th century as well. At the end of the 19th century and into the 20th century, the field of geology expanded even more. During this time, geologists developed the theories of continental drift, plate tectonics, and seafloor spreading.
A Ancient Greek and Roman Philosophers
In western science, the first written records of geological thought come from the Greeks and Romans. In the 1st century bc, for example, Roman architect Vitruvius wrote about building materials such as pozzolana, a volcanic ash that Romans used to make hydraulic cement, which hardened under water. Historian Pliny the Elder, in his encyclopedia, Naturalis Historia (Natural History), summarized Greek and Roman ideas about nature.
Science as an organized system of thought can trace its roots back to the Greek philosopher Aristotle. In the 4th century bc Aristotle developed a philosophical system that explained nature in a methodical way. His system proposed that the world is made of four elements (earth, air, fire, and water), with four qualities (cold, hot, dry, and wet), and four causes (material, efficient, formal, and final). According to Aristotle, elements could change into one another, and the earth was filled with water and air, which could rush about and cause earthquakes. Other philosophers of this era who wrote about earth materials and processes include Aristotle's student Theophrastus, the author of an essay on stones.
B Chinese Civilizations
Chinese civilizations developed ideas about the earth and technologies for studying the earth. For example, in 132 AD the Chinese philosopher Chang Heng invented the earliest known seismoscope. This instrument had a circle of dragons holding balls in their mouths, surrounded by frogs at the base. The balls would drop into the mouths of frogs when an earthquake occurred. Depending on which ball was dropped, the direction of the earthquake could be determined.
C Medieval and Renaissance Periods
The nature and origin of minerals and rocks interested many ancient writers, and mineralogy may have been the first systematic study to arise in the earth sciences. The Saxon chemist Georgius Agricola wrote De Re Metallica (On the Subject of Metals) following early work by both the Islam natural philosopher Avicenna and the German naturalist Albertus Magnus. De Re Metallica was published in 1556, a year after Agricola’s death. Many consider this book to be the foundation of mineralogy, mining, and metallurgy.
Medieval thought was strongly influenced by Aristotle, but science began to move in a new direction during the Renaissance Period. In the early 1600s, English natural philosopher Francis Bacon reasoned that detailed observations were required to make conclusions. Around this time French philosopher René Descartes argued for a new, rational system of thought. Most natural philosophers, or scientists, in this era studied many aspects of philosophy and science, not focusing on geology alone.
Studies of the earth during this time can be placed in three categories. The first, cosmology, proposed a structure of the earth and its place in the universe. As an example of a cosmology, in the early 1500s Polish astronomer Nicolaus Copernicus proposed that the earth was a satellite in a sun-centered system. The second category, cosmogony, concerned the origin of the earth and the solar system. The Saxon mathematician and natural philosopher Gottfried Wilhelm, Baron von Leibniz, in a cosmogony, described an initially molten earth, with a crust that cooled and broke up, forming mountains and valleys. The third category of study was in the tradition of Francis Bacon, and it involved detailed observations of rocks and related features. English scientist Robert Hooke and Danish anatomist and geologist Nicolaus Steno (Niels Stenson) both made observations in the 17th century of fossils and studied other geologic topics as well. In the 17th century, mineralogy also continued as an important field, both in theory and in practical matters, for example, with the work of German chemist J. J. Becher and Irish natural philosopher Robert Boyle.
D Geology in the 18th and 19th Centuries
By the 18th century, geological study began to emerge as a separate field. Italian mining geologist Giovanni Arduino, Prussian chemist and mineralogist Johan Gottlob Lehmann, and Swedish chemist Torbern Bergman all developed ways to categorize the layers of rocks on the earth's surface. The German physician Georg Fuchsel defined the concept of a geologic formation—a distinctly mappable body of rocks. The German scientist Abraham Gottlob Werner called himself a geognost (a knower of the earth). He used these categorizations to develop a theory that the earth's layers had precipitated from a universal ocean. Werner's system was very influential, and his followers were known as Neptunists. This system suggested that even basalt and granite were precipitated from water. Others, such as English naturalists James Hutton and John Playfair, argued that basalt and granite were igneous rocks, solidified from molten materials, such as lava and magma. The group that held this belief became known as Volcanists or Plutonists.
By the early 19th century, many people were studying geologic topics, although the term geologist was not yet in general use. Scientists, such as Scottish geologist Charles Lyell, and French geologist Louis Constant Prevost, wanted to establish geology as a rational scientific field, like chemistry or physics. They found this goal to be a challenge in two important ways. First, some people wanted to reconcile geology with the account of creation in Genesis (a book of the Old Testament) or wanted to use supernatural explanations for geologic features. Second, others, such as French anatomist Georges Cuvier, used catastrophes to explain much of earth’s history. In response to these two challenges, Lyell proposed a strict form of uniformitarianism, which assumed not only uniformity of laws but also uniformity of rates and conditions. However, assuming the uniformity of rates and conditions was incorrect, because not all processes have had constant rates throughout time. Also, the earth has had different conditions throughout geologic time—that is, the earth as a rocky planet has evolved. Although Lyell was incorrect to assume uniformity of rates and conditions, his well reasoned and very influential three-volume book, Principles of Geology, was published and revised 11 times between 1830 and 1872. Many geologists consider this book to mark the beginning of geology as a professional field.
Although parts of their theories were rejected, Abraham Gottlob Werner and Georges Cuvier made important contributions to stratigraphy and historical geology. Werner's students and followers went about attempting to correlate rocks according to his system, developing the field of physical stratigraphy. Cuvier and his co-worker Alexandre Brongniart, along with English surveyor William Smith, established the principles of biostratigraphy, using fossils to establish the age of rocks and to correlate them from place to place. Later, with these established stratigraphies, geologists used fossils to reconstruct the history of life's evolution on earth.
E Age of Geologic Exploration
In the late 18th and the 19th centuries, naturalists on voyages of exploration began to make important contributions to geology. Reports by German natural historian Alexander von Humboldt about his travels influenced the worlds of science and art. The English naturalist Charles Darwin, well known for his theory of evolution, began his scientific career on the voyage of the HMS Beagle, where he made many geological observations. American geologist James Dwight Dana sailed with the Wilkes Expedition throughout the Pacific and made observations of volcanic islands and coral reefs. In the 1870s, the HMS Challenger was launched as the first expedition specifically to study the oceans.
Expeditions on land also led to new geologic observations. Countries and states established geological surveys in order to collect information and map geologic resources. For example, in the 1860s and 1870s Clarence King, Ferdinand V. Hayden, John Wesley Powell, and George Wheeler conducted four surveys of the American West. These surveys led to several new concepts in geology. American geologist Grove Karl Gilbert described the Basin and Range Province and first recognized laccoliths (round igneous rock intrusions). Reports also came back of spectacular sites such as Yellowstone, Yosemite, and the Grand Canyon, which would later become national parks. Competition between these survey parties finally led the Congress of the United States to establish the U.S. Geological Survey in 1879.
F Geologic Time
Determining the age of the earth became a renewed scholarly effort in the 19th century. Unlike the Greeks and most eastern philosophers, who considered the earth to be eternal, western philosophers believed that the planet had a definite beginning and must have a measurable age. One way to measure this age was to count generations in the Bible, as the Anglican Archbishop James Ussher did in the 1600s, coming up with a total of about 6000 years. In the 1700s, French natural scientist George Louis Leclerc (Comte de Buffon) tried to measure the age of the earth. He calculated the time it would take the planet to cool based on the cooling rates of iron balls and came up with 75,000 years. During the 18th century, James Hutton argued that processes such as erosion, occurring at observed rates, indicated an earth that was immeasurably old. By the early 19th century, geologists commonly spoke in terms of "millions of years." Even religious professors, such as English clergyman and geologist William Buckland, referred to this length of time.
Other means for calculating the age of the earth used in the 19th century included determining how long it would take the sea to become salty and calculating how long it would take for thick piles of sediment to accumulate. Irish physicist William Thomson (Lord Kelvin) returned to Buffon's method and calculated that the earth was no more than 100 million years old. Meanwhile, Charles Darwin and others argued that evolution proceeded slowly enough that it required at least hundreds of millions of years.
With the discovery of radioactivity in 1896 by French physicist Henri Becquerel, scientists, such as British physicist Ernest Rutherford and American radiochemist Bertram Boltwood, recognized that the ages of minerals and rocks could be determined by radiometric dating. By the early 20th century, Boltwood had dated some rocks to be more than 2 billion years old. During this time, English geologist Arthur Holmes began a long career of refining the dates on the geologic time scale, a practice that continues to this day.
G Theory of Continental Drift
In 1910 American geologist Frank B. Taylor proposed that lateral (sideways) motion of continents caused mountain belts to form on their front edges. Building on this idea in 1912, German meteorologist Alfred Wegener proposed a theory that came to be known as Continental Drift: He proposed that the continents had moved and were once part of one, large supercontinent called Pangaea. Wegener was attempting to explain the origin of continents and oceans when he expanded upon Taylor’s idea. His evidence included the shapes of continents, the physics of ocean crust, the distribution of fossils, and paleoclimatology data.
Continental drift helped to explain a major geologic issue of the 19th century: the origin of mountains. Theories commonly called on the cooling and contracting