MODELS OF THE EARTH

Unit Overview
This unit will look into the many tools developed by scientists to study our Earth. These tools in turn, have brought about new discoveries and areas of research in Earth science. Many technologies such as satellite global positioning systems and topographic maps are used by everyday people to make their lives comfortable and safe.

Unit Directions

Read the following text on Earth models, study the illustrations, complete all activities, and then answer the test questions. Key terms will be in bold type.

GLOSSARY OF KEY TERMS

contour lines: imaginary lines that connect equal areas of elevation on a topographic map

globe: a map of the world or a celestial map on a sphere, allowing for a more accurate representation of the Earth's surface than can be shown on a flat map

map: a flat, graphic representation of the Earth

model: a simplified description of a complex entity or process

oblate spheroid: a spherical shape that is a slightly distorted sphere. The distortion occurs in the middle of the sphere where there is a bulge

pure science: the study of the natural world through observation, identification, description, experimental investigation, and theoretical explanations

relief maps: maps having shading or color to represent points of different elevation

technology: the application of scientific advances to benefit humanity

thermodynamics: the study of the processes that involve the transformation of heat from hotter bodies to cooler bodies

topographic maps: maps that show natural and man-made features of an area using contour lines (lines of equal elevation) to portray the size, shape, and elevation of the features

satellite: any object, man-made or natural that orbits another object

What shape is our planet?

That sounds like a pretty simple question, right? Most of us would quickly say, “Round.” But the Earth is not perfectly round! It has an oblong shape like all the other planets. This is caused by the spinning of the planets that forces the matter to compress in the middle of the sphere-shaped planetary bodies, and a distortion in their shape is created. Our Earth is almost a sphere, but not quite, so its shape is an oblate spheroid. Oblate describes the oblong shape and spheroid tells us that the Earth is a nearly sphere-shaped planet.

The first picture shows an oblate spheroid from the side. You can see that it is narrower at the top and bottom and wider in the middle. The picture on the right shows a top view of the oblate spheroid. In this view, the shape looks perfectly round.

How did scientists prove the oblate spheroid shape?

Scientists can not make a statement about the Earth’s shape without evidence. So what is the evidence that supports the oblate spheroid shape?

· Pictures from outer space: Astronauts and satellites have provided beautiful photographs that help support the shape theory. It is, however, very hard to detect by looking at photographs because the shape is so close to a perfect sphere.

· Measurements: Accurate measurements are kept of the movement of the stars and Sun. The movements of these heavenly bodies would appear differently if the Earth were a perfect sphere. Another set of measurements come from right here on Earth. Scientists collect calculations on gravity’s affect on different objects. As an object moves away from the Earth’s core, its weight changes. If the Earth were perfectly round, the weight of the object would be the same all around the Earth as long as it was measured at the same elevation. On Earth, objects weigh a little more at the poles and a little less at the equator due to the oblate spheroid shape.

What types of models are used to represent Earth?

· A model is a visual representation, a mathematical equation, or a set of rules that let us study an object or concept that is not easily observed. Many times a model is used when an object is too large or too small to study and the model aids in our understanding. For instance, we can not see a single skin cell with the naked eye, so a scientist will use a poster or plaster model of the cell to study its parts and structure. The Earth is too big for us to take in by just looking outside, so we invent physical models to make observations much easier. The globe is a familiar model used by many to look at the complete structure of the Earth.

· People use globes for a variety of reasons. We can study the continents of the world, the many bodies of water, latitudinal and longitudinal lines, and political boundaries. A person can study the Earth as a whole using a globe. The globe increases visual accuracy and allows a viewer to create a mental map and see the relationship between continents, oceans, and climatic differences. Size, shape, distance and directions are accurately shown on a globe. Globes do not distort the major features of our Earth.

Maps

· A map is a flat, graphic representation of the Earth. Maps are drawn for a variety of reasons. Most people are familiar with maps that are used to look up directions for traveling from one place to another.

· The map above shows the area around Steubenville, Ohio. It displays major roads and the names of towns. The Ohio River is the blue winding line in the middle of the map. Other maps will give us different information.

· World maps show the entire world at a glance. But because a map is flat, there is distortion in the size, shape and distance of features such as countries and continents. The map above shows the continents and oceans. Other world maps can show political boundaries (countries), seismic activity, and weather patterns.

Weather maps detail information that explains weather conditions across a specific area. These maps often come with keys or special symbols that represent the various weather conditions.

· Relief Maps are maps having shading or color to represent points of different elevation. This type of map usually contains an explanation or key to help a user read the map. The map below is a relief map of Arizona.

The colors indicate elevation above sea level

· Orange and red areas in SW AZ are lowest

· Blue and purple are higher

· Green and brown areas in N and E AZ are even higher

· The isolated pink color mountain areas are the highest.

· Topographic Maps are maps that show natural and man-made features of an area using contour lines (lines of equal elevation) to portray the size, shape, and elevation of the features. Contour lines are imaginary lines that connect equal areas of elevation. The contour lines make it possible for map users to measure the height of mountains, the depth of bodies of water, and the slope of hills. Topographic maps usually have a key that defines symbols representing other features such as wooded areas, buildings, and streams.

This is a Topographic Map of Vulture Peak in Arizona.

This topographic map is used by scientists to record data to find relationships between  bark beetle outbreaks in Central Europe and site, host, environmental conditions (air pollution), and spruce bark beetle populations.

Satellite Imaging

· A satellite is any object, man-made or natural that orbits another object. Our moon is a natural satellite of the Earth. But did you know that there are over 8,000 artificial objects orbiting the Earth? About 2,500 of these objects are man-made satellites, some of which currently work and others that no longer work. The rest of the orbiting objects are “space junk”, such things as rocket parts and pieces of metal that have broken off of satellites. Man-made satellites perform many functions such as sending and receiving weather data, military information, radio and television transmission, and communication transmissions. Scientists use satellites to collect a wide variety of information for research that helps us understand our changing Earth.

· Geostationary Satellite Systems: These satellites orbit the Earth at the same rate that the Earth rotates on its axis. This means that the satellite keeps imaging the same area on Earth. These satellites orbit around 35,785 km (22,235 miles) above the Earth and they can image almost half of the sphere from that position.

· Space Stations and the Space shuttle: These vehicles perform a variety of functions. One of the functions is photography of the Earth. They send back photographs to scientists all over the world.

Earth’s Interior Models

Scientists have collected data for many years on the Earth’s movements. They have studied seismic activity (earthquakes) and volcanic eruptions. All of this data helps scientists compose a model of our Earth’s interior structure. No one has ever seen the interior of the Earth, but theories supported by a great deal of evidence have lead scientists to believe that the Earth’s interior looks like the picture below.

Scientists continually gather information to improve the model of the Earth’s interior. They use measurements of the speed that seismic waves move through the various compositions in the Earth’s crust. Waves will travel at different speeds through solids than they will through the molten layers. Scientist use these wave speeds to calculate the depth of each layer of Earth.

Scientists also use the thermodynamics of Earth to study its interior. Thermodynamics is the study of the processes that involve the transformation of heat into mechanical work, of mechanical work into heat, or the flow of heat from a hotter body to a colder body.

The Relationship between Science and Technology

We have just finished a study of how scientists composed theories and models of our Earth. Many observations and experimental data have been put together to form the models. The study of nature is advanced in two ways: pure science and technology.

· Pure science is the study of the natural world through observation, identification, description, experimental investigation, and theoretical explanations. Scientists write books and research papers that present the pure science to other scientists. As scientists study nature, they invent many tools that in turn help them collect more data. These tools are examples of technology.

· Technology is the application of scientific advances to benefit humanity. As new technology is invented, new information about nature helps us form new theories and models of our world. For example, the microscope was invented after scientists put together all they knew about refractive and reflective lenses, and the magnification of objects. When they used the microscope, a great deal of new information came about from observing objects closely and new discoveries were made because some things were never seen by our naked eye.

Take a few minutes to review this unit and then write down 3 examples of science and 3 examples of technology in the unit.