Answer:
A primary source is anything that gives you direct evidence about the people, events, or phenomena that you are researching. Primary sources will usually be the main objects of your analysis. If you are researching the past, you cannot directly access it yourself, so you need primary sources that were produced at the time by participants or witnesses (e.g. letters, photographs, newspapers).
A secondary source is anything that describes, interprets, evaluates, or analyzes information from primary sources. Common examples include: 1. Books, articles and documentaries that synthesize information on a topic 2. Synopses and descriptions of artistic works 3. Encyclopedias and textbooks that summarize information and ideas 4. Reviews and essays that evaluate or interpret something When you cite a secondary source, it’s usually not to analyze it directly.
Examples of sources that can be primary or secondary:
A secondary source can become a primary source depending on your research question. If the person, context, or technique that produced the source is the main focus of your research, it becomes a primary source.
To determine if something can be used as a primary or secondary source in your research, there are some simple questions you can ask yourself: 1. Does this source come from someone directly involved in the events I’m studying (primary) or from another researcher (secondary)? 2. Am I interested in analyzing the source itself (primary) or only using it for background information (secondary)?
Most research uses both primary and secondary sources. They complement each other to help you build a convincing argument. Primary sources are more credible as evidence, but secondary sources show how your work relates to existing research.
The lithosphere, which is the rigid outermost shell of a planet (the crust and upper mantle), is broken up into tectonic plates. The Earth's lithosphere is composed of seven or eight major plates (depending on how they are defined) and many minor plates. Where the plates meet, their relative motion determines the type of boundary: convergent, divergent, or transform. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along these plate boundaries. The relative movement of the plates typically ranges from zero to 100 mm annually.[2]
Tectonic plates are composed of oceanic lithosphere and thicker continental lithosphere, each topped by its own kind of crust. Along convergent boundaries, subduction carries plates into the mantle; the material lost is roughly balanced by the formation of new (oceanic) crust along divergent margins by seafloor spreading. In this way, the total surface of the lithosphere remains the same. This prediction of plate tectonics is also referred to as the conveyor belt principle. Earlier theories, since disproven, proposed gradual shrinking (contraction) or gradual expansion of the globe.[3]
Tectonic plates are able to move because the Earth's lithosphere has greater strength than the underlying asthenosphere. Lateral density variations in the mantle result in convection. Plate movement is thought to be driven by a combination of the motion of the seafloor away from the spreading ridge (due to variations in topography and density of the crust, which result in differences in gravitational forces) and drag, with downward suction, at the subduction zones. Another explanation lies in the different forces generated by tidal forces of the Sun and Moon. The relative importance of each of these factors and their relationship to each other is unclear, and still the subject of much debate.
The correct answer is - They formed long ago, and erosion has beveled them to their present elevation.
The Appalachian Mountain Range is one of the oldest mountain ranges on the planet. They have formed in the Ordovician Period, around 480 million years ago. When they formed and were at their peak, the Appalachians were much larger and higher than what they are in the present. The reason for their decline in size is attributed to the erosion. The erosion is a process that removes the material from its original position. This process has been influencing, at different rates, the Appalachians for almost half a billion years. Even though the erosion is not a process that acts very quickly, when put the time that it influenced these mountains we will see that it managed to lower them significantly. That process continues in the present, and in the manner in which the continents are moving, there shouldn't be any force that will help lift up the Appalachians again, but instead they will continue to shrink until they are flattened in the distant future.
