GPS, or the Global Positioning System, is a network of satellites in orbit around the Earth that may give us a precise location of either ourselves or a point of interest. It began as early as 1973 with military defense in mind but was later expanded for general use in the early 1990s.
How does GPS work?
We often take GPS for granted because it is ubiquitous, found on phones, mobile devices, stand-alone units, and embedded in the navigation systems of our cars and many other products. It works by analyzing how long it takes for a time signal to travel from one of the three to four satellites to your receiver. This process is called trilateration. When satellites are above the horizon, the results are much more accurate.
How many GPS satellites are there?
Although we need only 24 functioning satellites in order to provide an accurate measurement of a location, there are currently 69 satellites orbiting the Earth. Some are not functional and had to be replaced by a working unit, while others are on reserve in case they are needed.
How does a GPS unit know where I am?
Individual Global Positioning System (GPS) units on the Earth receive information from a U.S. military-run system of 24 satellites that circle the Earth and provide precise time and location data. The individual GPS unit receives data from three or more satellites that triangulate its absolute location on the Earth’s surface. If you are carrying such a device, your absolute location is the same as that of the device.
How can GPS keep me from getting lost?
A GPS unit provides precise latitude and longitude for the location of the device. By using a handheld GPS unit or a GPS-enabled device, along with a map that provides latitude and longitude (such as a topographic map), you can determine your precise location on the Earth’s surface. This is a valuable tool for those who hike or travel in remote regions and for ships at sea. GPS is now widely available in cars; as stand-alone, portable, pocket-sized devices; on phones; and even on the boxes that ship products that you buy. In short, GPS is used in all aspects of our lives.
THE EARTH’S MATERIALS AND INTERNAL PROCESSES
What are the three main layers of the interior of the Earth?
Scientists do not know very much about what is below the surface of our planet. But we do know that it is divided into three layers: crust, mantle (upper and lower), and core (outer and inner).
How thick is the Earth’s crust?
The thickness of the Earth’s crust varies at different points around the planet. Under continents, the crust is approximately 27–31 miles (45–50 km) thick, but under the oceans, it is a mere 6.2 miles (10 km) thick, usually surrounded by an 18-mile- (30-km-) thick contour.
What did Alfred Wegener discover?
Although Wegener was not the first to discover that the continents seem to appear to fit together like pieces of a jigsaw puzzle, he was the first to create a theory that the continents seemed to have drifted apart, in 1912. His original paper was entitled “The Formation of the Major Features of the Earth’s Crust (Continents and Oceans).” It was not until long after his death in 1930 that modern technology and scientific analyses proved that he was correct.
What is continental drift?
The Earth is divided into massive pieces of crust that are called tectonic plates. These plates lie wedged together like a puzzle. The plates slowly move, crashing into each other to form mountain ranges, volcanoes, and earthquakes. The plates are like rafts floating on water; this is called continental drift. By 1968, the theory of continental drift was gradually replaced by the theory of plate tectonics.
This contour map indicates the differing levels of thickness in the Earth’s crust as marked in ten-kilometer (six-mile) intervals.
How do we know that the continents were once joined together?
There is extensive evidence, dating back many millions, perhaps billions, of years, that the continents were joined together. Fossil evidence of plant and animal life that are similar have been found on different continents, as well as similar glacial sediment.
How many tectonic plates are there?
There are seven significant plates on the planet. Some of the largest include the Eurasian Plate, North American Plate, South American Plate, African Plate, Indo-Australian Plate, Pacific Plate, and Antarctic Plate. Some smaller plates are located between the major plates. The smaller plates include the Arabian Plate (containing the Arabian Peninsula), the Nazca Plate (located to the west of South America), the Philippine Sea Plate (located southeast of Japan, containing the northern Philippine islands), the Indian Plate (containing Southeast Asia, India, and South China to Eastern Indonesia), the Cocos Plate (located southwest of Central America), the Juan de Fuca Plate (just off the coast of Oregon, Washington, and Northern California), and the Caribbean Plate (beneath Central America and the Caribbean Sea).
Pangea was a supercontinent that existed about 200 million years ago. It gradually separated into two large continents—Laurasia and Gondwana—about 120 million years ago, and then those continents divided further over time.
What type of rocks are formed by lava?
Igneous rocks are formed when liquid magma under the surface of the Earth, or lava on the surface of the Earth, cools and hardens into rock.
What type of rocks are formed from particles?
Sedimentary rocks are formed by the accumulation and squeezing together of layers of sediment (particles of rock or remains of plant and animal life) at the bottom of rivers, lakes, and oceans or even on land. The continual accumulation of more and more layers of sediment places a great amount of pressure on the lowest layers of sediment and, over time, compresses them into rock.
What are recycled rocks?
Metamorphic rocks are rocks that had a prior existence as sedimentary, igneous, or other metamorphic rocks. Underground heat and pressure metamorphose or change one type of rock into another, creating a metamorphic, or recycled, rock.
What type of sand do we often see on beaches near volcanoes?
Because the content of the sediment near volcanoes is comprised of dark black igneous rock, the resulting beach sand in such places as Hawaii and Indonesia is actually a dark brown or even black in color.
Which is larger, clay or sand?
A single grain of sand is 1,500 times larger than a grain of clay.
What is a dike?
A dike is magma that has risen up through a crack between layers of rock. When this magma solidifies, it becomes very solid rock. If the rock around it is eroded, a dike can form
