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  • April Koch April teaches high school science and holds a master's degree in education. Learn how scientists determine the ages of rocks and fossils. We'll explore both relative and numerical dating on our quest to understand the process of geological dating. Along the way, we'll learn how stratigraphic succession and radioactive decay contribute to the work of paleontologists.

    Dating Dinosaur Fossils Consider the following scenario: Paul the Paleontologist is a very famous scientist who has studied dinosaur bones all over the world.

    Recently, he appeared on the evening news to talk about a new dinosaur he just discovered. The dinosaur is called superus awesomus. Paul says he can tell from the fossils that superus awesomus lived on Earth about million years ago.

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    Paul is super awesome, so I'm going to take him at his word. But really, how do scientists figure out how old their dinosaur bones are? And, what about other findings like fossil fish, plants and insects? Scientists are always spouting information about the ages of rocks and fossils.

    How do they know these ages? Well, they figure it out using two different methods: Let's find out more about these geological dating methods in order to understand how Paul the Paleontologist can be so sure about the age of his dinosaur fossils.

    Relative Dating The first method that scientists use to determine the age of rocks is relative dating. In this method, scientists compare different layers of rock to determine an ordered sequence of events in geologic history.

    That means they don't really know how old their rocks actually are. The key in relative dating is to find an ordered sequence.

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    Scientists piece together a story of how one event came before or after another. Relative dating cannot tell us the actual age of a rock; it can only tell us whether one rock is older or younger than another.

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    The railroad, the steamship, and the telegraph had a profound impact on logistic method during the last half of the 19th century. Beginning with the Crimean War —56telegraphic communication became an indispensable tool of command, intelligence, and operational coordination, particularly in controlling rail… Early development Messengers have been employed in war since ancient times and still constitute a valuable means of communication.

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    Alexander, Hannibal, and Caesar each developed an elaborate system of relays by which messages were carried from one messenger post to another by mounted messengers traveling at top speed. They were thus able to maintain contact with their homelands during their far-flung campaigns and to transmit messages with surprising speed. Genghis Khan at the close of the 12th century not only emulated his military predecessors by establishing an extensive system of messenger posts from Europe to his Mongol capital but also utilized homing pigeons as messengers.

    As he advanced upon his conquests he established pigeon relay posts across Asia and much of eastern Europe. He was thus able to use these messengers to transmit instructions to his capital for the governing of his distant dominions.

    Before the end of the 18th century European armies used the visual telegraph system devised by Claude Chappeemploying semaphore towers or poles with movable arms. The Prussian army in assigned such visual telegraph duties to engineer troops.

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    At the same time that these elementary methods of signal communication were being evolved on land, a comparable development was going on at sea.

    Early signaling between naval vessels was by prearranged messages transmitted by flagslights, or the movement of a sail. Codes were developed in the 16th century that were based upon the number and position of signal flags or lights or on the number of cannon shots.

    In the 17th century the British admiral Sir William Penn and others developed regular codes for naval communication; and toward the close of the 18th century, Admiral Richard Kempenfelt developed a plan of flag signaling similar to that now in use. Later Sir Home Popham increased the effectiveness of ship-to-ship communication by improved methods of flag signaling.

    The advent of electrical signaling Despite the early pioneering efforts on land and sea the real development of signal communication in war did not come until after invention of the electric telegraph by Samuel F.

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    In his successful demonstration of electric communication between Washington, D. The development of the Morse Code of dots and dashes used with key and sounder was soon used to augment the various means of visual signaling. The first application of the telegraph in time of war was made by the British in the Crimean War inbut its capabilities were not well understood, and it was not widely used.

    Three years later, in the Indian Mutinythe newly established telegraph, which was controlled by the British, was a deciding factor. In the American Civil War —65wide use was made of the electric telegraph.

    In addition to its employment in spanning long distances under the civilian-manned military telegraph organization, mobile field service was provided in the Union army by wagon trains equipped with insulated wire and lightweight poles for the rapid laying of telegraph lines.

    Immediately before and during the Civil War visual signaling also received added impetus through development of a system, applying the Morse code of dots and dashes, that spelled out messages with flags by day and lights or torches by night. Another development for light signaling placed a movable shutter, controlled by a key, in front of a strong light. An operator, opening and closing the shutter, could produce short and long flashes to spell out messages in Morse code.

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    Simultaneously, the Prussian and French armies also organized mobile telegraph trains. During the short, decisive Prussian campaign against Austria infield telegraph enabled Count Helmuth von Moltkethe Prussian commander, to exercise command over his distant armies.

    Soon afterward the British organized their first field telegraph trains in the Royal Engineers.

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    Another instrument was added to the techniques for visual signaling through the development of the heliograph. It employed two adjustable mirrors so arranged that a beam of light from the sun could be reflected in any direction. The beam was interrupted by a key-operated shutter that permitted the formation of the dots and dashes of the Morse code. Where climatic conditions were favourable this instrument found much use, notably by the British army in India and the U.

    Army in the American Southwest. Because consistency and regularity of sunshine were important, the heliograph was never widely adopted throughout the armies of continental Europe. The invention of the telephone in was not followed immediately by its adoption and adaptation for military use.

    This was probably due to the fact that the compelling stimulation of war was not present and to the fact that the development of long-distance telephone communication was not achieved for many years. The telephone was used by the U. This military use was not extensive, and it made little material contribution to the development of voice telephony.

    Before the outbreak of World War I, military adaptation of the telephone did take place, but its period of growth had not yet arrived. Near the close of the 19th century, a new means of military signal communication made its appearance—the wireless telegraph, or radio. The major powers throughout the world were quick to see the wonderful possibilities for military and naval signaling. Development was rapid and continuous, and, byit was adopted and in extensive use by all the armies and navies of the world.

    It soon became apparent that wireless telegraphy was not an unmixed blessing to armies and navies, because it lacked secrecy and messages could be heard by the enemy as well as by friendly forces.

    This led to the development of extensive and complicated codes and ciphers as necessary adjuncts to military signaling. The struggle between the cryptographer and the cryptanalyst expanded greatly with the adoption of radio and continued to be a major factor affecting its military use. From World War I to The onset of World War I found the opposing armies equipped to a varying degree with modern means of signal communication but with little appreciation of the enormous load that signal systems must carry to maintain control of the huge forces that were set in motion.

    The organization and efficiency of the armies varied greatly.

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    At one end of the scale was Great Britain, with a small but highly developed signal service; and at the other end stood Russia, with a signal service inferior to that of the Union Army at the close of the American Civil War.

    The fact that commanders could not control, coordinate, and direct huge modern armies without efficient signal communication quickly became apparent to both the Allies and the Central Powers. The Germans, despite years of concentration on the Schlieffen Planfailed to provide adequately for communication between higher headquarters and the rapidly marching armies of the right wing driving through Belgium and northern France.

    This resulted in a lack of coordination between these armies, which caused a miscarriage of the plan, a forced halt in the German advance, and the subsequent withdrawal north of the Marne. On the Allied side, the debacle of the Russian forces in East Prussia—a crushing defeat at the hands of General Paul von Hindenburg in the Battle of Tannenberg —was largely due to an almost total lack of signal communication.

    As the war progressed there was a growing appreciation of the need for improved electrical communications of much greater capacity for the larger units and of the need within regiments for electrical communications, which had heretofore been regarded as unessential and impractical.

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    Field telephones and switchboards were soon developed, and those already in existence were improved. An intricate system of telephone lines involving thousands of miles of wire soon appeared on each side.

    Pole lines with many crossarms and circuits came into being in the rear of the opposing armies, and buried cables and wires were laid in the elaborate trench systems leading to the forwardmost outposts.

    The main arteries running from the rear to the forward trenches were crossed by lateral cable routes roughly parallel to the front. Thus, there grew an immense gridwork of deep buried cables, particularly on the German side and in the British sectors of the Allied side, with underground junction boxes and test points every few hundred yards.

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    The French used deep buried cable to some extent but generally preferred to string their telephone lines on wooden supports set against the walls of deep open trenches.

    Thus electrical communication in the form of the telephone and telegraph gradually extended to the smaller units until front-line platoons were frequently kept in touch with their company headquarters through these mediums.

    Despite efforts to protect the wire lines, they were frequently cut at critical times as the result of the intense artillery fire. This led all the belligerents to develop and use radio wireless as an alternate means of communication.

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    Prewar radio sets were too heavy and bulky to be taken into the trenches, and they also required large and highly visible aerials. Radio engineers of the belligerent nations soon developed smaller and more portable sets powered by storage batteries and using low, inconspicuous aerials. Although radio equipment came to be issued to the headquarters of all units, including battalions, the ease of enemy interception, the requirements for cryptographing or encoding messages, and the inherent unreliability of these early systems caused them to be regarded as strictly auxiliary to the wire system and reserved for emergency use when the wire lines were cut.

    Visual signaling returned to the battlefield in World War I with the use of electric signal lamps. Pyrotechnics, rockets, Very pistols, and flares had a wide use for transmitting prearranged signals. Messenger service came to be highly developed, and motorcycle, bicycle, and automobile messenger service was employed. Homing pigeons were used extensively as one-way messengers from front to rear and acquitted themselves extremely well.

    Dogs were also used as messengers and, in the German army, reached a high degree of efficiency. A new element in warfare, the airplaneintroduced in World War I, immediately posed a problem in communication.