The Richard Russell Mesquite ISD Planetarium boasts a foyer with many exciting artifacts that are worth seeing. Below are descriptions of the items that we have.
The Earth’s outer layer, the lithosphere, consists of a number of rigid, moving pieces called plates. These lithospheric plate rest on the asthenosphere, which is partially molten igneous rock. As the molten rock flows, very large and slow-moving convection currents are formed. Within the currents, material expands and rises as it is heated, and contracts and sinks as it cools. The currents in the asthenosphere cause the lithospheric plates to move; some plates are pushed apart, some together, and other slide past each other. The plate boundaries are the epicenters of earthquakes and the sites of most volcanic activity.
The study of the formation and movement of the lithospheric plates is called plate tectonics. This model demonstrates the complex relationships involved in this process.
Divergent oceanic boundaries are places where the lithospheric plates are moving apart. Most diverging boundaries have mid-ocean ridges (2) with deep rift valleys (3) along their entire length. Rising convection currents (indicated by arrows) in the asthenosphere (1) carry largely gas-free molten rock into the rift valleys, where new rocks solidify, forcing the ocean floor to spread. Lava from rift eruptions may spread over many kilometers (12). The rift valleys are broken into segments by faults called fracture zones (17). Movements along the fractures zones have been found to be the source of the earthquakes that occur along the ridge.
The left side of the model illustrates a type of transform boundary, where one plates is sliding past another horizontally, causing little or no subduction/accretion. However, because the edges are rough, they catch on one another, allowing stress to build up. When this stress is released suddenly, earthquakes may occur. In the model, sedimentation (5) has filled in a large part of the area but a basin (6) can still be seen. The upper part of the model (16) can be moved slightly to simulate the motion at a transform boundary.
When one plate collides with another and slides beneath it, a deep-sea trench (7) is formed at the subduction boundary (8). When this trench is formed by the convergence of two ocean plates, it is bordered by a chain of volcanic islands on the overriding ocean plate. When an ocean plate (11) converges with a continental plate and the deep-sea trench is bordered by mountains and volcanoes (9) on the continental plate. The volcanoes occur when magma is forced up through cracks formed in the continental plate (10) as the ocean plate slides under it. The subducted part of the ocean plate is recycled into the asthenosphere.
The left side of the model shows a continental plate converging with an ocean plate. Thick, gaseous magma (13) has formed at the subduction boundary. Explosive subduction boundary eruption, consisting mainly of lava fragments, have formed a steep-sided cinder cone volcano (14). Even though the subducting plate as a whole sinks smoothly into the deep-sea subduction trench, the deepest part of the plate breaks into smaller pieces which become locked in place (15) for long periods of time. Sudden shifting of these pieces generates large earthquakes which can move the land several meters.
Neither rocks nor minerals have been collected and returned from the surface of Mars. Our knowledge of its surficial composition is limited to Martian meteorites and geochemical analysis or rocks and minerals by spacecraft on the surface of Mars. The rocks and minerals displayed are believed to be the most common at this time.
On Mars, sulfur has not been identified in its native form and is instead a component of Martian soil and minerals. The soil on mars contains between 5 and 15 wt% sulfur. Minerals containing sulfur, such as gypsum, have also been identified on the Martian surface. These minerals are important to the geologic history of mars as they indicate the presence of liquid water on the surface. Although native sulfur has not been identified on mars, its history of volcanism increased the likelihood of its existence.
Hematite is one of the dominant components of the Martian soil. Hematite has not been identified as a primary mineral component within Martian rocks. It has been found as a secondary alteration mineral both within the weathering rind of rocks and also replacing primary minerals within rocks. Unusual spherical shaped hematite or ‘blueberries’ have also been identified on the Martian surface. They are about 4 mm in diameter and were identified in a Martian sedimentary sandstone by the Mars rover, Opportunity. Scientists believe iron and sulfate rich fluids moving through the sandstone chemical precipitate the blueberries within the rock. The identification of hematite on the surface of mars is important because it suggests the presence of water at the surface at some time during the planet’s history.
On mars gypsum is a common component of the layered sedimentary deposits in the north and south poles as well as those found within canyons. A European satellite, OMEGA identified gypsum in Valles Marineris and within the layered deposits of the north pole. Mars rover, Opportunity, identified several evaporitic minerals including gypsum at its landing site in 2004. Gypsum fragments have also been identified within deposits on the Martian surface is important to reconstructing its geologic history. Evaporates indicate large bodies of water were once present on Mars and that they underwent periods of evaporation to allow for evaporitic deposition.
4.Vesicular Basalt (rock)
Basalts are the most common material found on the Martian surface. On Mars, basalts compose the several shield volcanoes of the Tharsis bulge as well as the extensive lava plains on the surface.
5.Arenite (sandstone) (rock)
Arenites found on mars are much different than those found on earth. On earth, quartz is a common mineral component of igneous rocks; however, quartz-rich igneous rocks have not been identified on the Martian surface. The most common igneous rock on Mars is basalt, whose common mineral components are plagioclase, olivine, and pyroxene. Since basalt is the most common rock exposed on the Martian surface, arenites likely have a basaltic composition. Like earth, both water and wind generated arenites exist on the Martian surface as identified by mars rover, Opportunity at its landing site.
Martian breccias are dominantly formed as a result of meteor impacts, although extrusive volcanic breccias also exist. Martian impact breccias form when an extraterrestrial rock impacts the surface of Mars and the rocks on the surface undergo fragmentation. These fragments, or clasts, are ejected from the newly formed crater and consolidate during or after the impact. Clasts within Martian breccias are composed of rock fragments. Since Mars’ surface is dominantly composed of oxidized basalts, impacts on its surface has resulted in the formation of basaltic breccias.
Fossils are the preserved remains of plants or animals. For such remains to be considered fossils, scientists have decided they have to be over 10,000 years old. There are two main types of fossils, body fossils and trace fossils. Body fossils are the preserved remains of a plant or animal’s body. Trace fossils are the remains of the activity of an animal, such as preserved trackways, footprints, fossilized egg shells, and nests.
When asked what a fossil is, most people think of petrified bones or petrified wood. Permineralization is a process. For bone to be permineralized, the body must first be quickly buried. Second, ground water fills up all the empty spaces in body, even the cells get filled with water. Third, the water slowly dissolves the organic material and leaves minerals behind. By the time permineralization is done, what was once bone is now a rock in the shape of a bone.
When an animal or plant dies, it may fall into mud or soft sand and make an impression or mark in the dirt. The body is then covered by another layer of mud or sand. Over time, the body falls apart and is dissolved. The mud or sand can harden into rock preserving the impression of the body, leaving an animal or plant shaped hole in the rock. This hole is called a mold fossil. If the mold becomes filled over time with other minerals the rock is called a cast fossil. (http://www.kidsdinos.com/what-are-fossils/)
Fossils give us information about how animals and plants lived in the past. Once people began to recognize that some fossils looked like living animals and plants, they gradually began to understand what they were. They realized they were actually the ancestors of today's plants and animals.
Some fossils are easy to identify and look like plants and animals alive today.
While we can easily recognize and identify some fossils, many fossils represent animals that no longer exist on Earth. We only know about extinct groups like dinosaurs, ammonites and trilobites through fossils.
Some animals and plants are only known to us as fossils. By studying the fossil record, we can tell how long life has existed on Earth, and how different plants and animals are related to each other. Often we can work out how and where they lived, and use this information to find out about ancient environments. (http://www.oum.ox.ac.uk/thezone/fossils/intro/proof.htm)
Making up the majority of the Earth's crust, rock is usually defined as a mixture of common minerals. Rocks can be hard or soft, as small as a grain or as large as a building. They have been an integral part of the history of mankind, first being used as tools for hunting and defense, and as a building materials to construct shelters and monuments. Combined with the effects of tectonics, weathering and vegetation, rocks define the natural landscapes we see around us. The minerals and metals we find in rocks are essential to the prosperity and cultural splendor of human civilization.
There are many kinds of rock, and they can be classified in a number of ways. However, geologists classify rocks based on how the rocks were formed. The three classes are igneous rocks (formed directly from liquid rock), metamorphic rocks (formed by direct alteration of existing rocks), and sedimentary rocks (formed by eroded materials from other rocks). (http://earth.rice.edu/mtpe/geo/geosphere/topics/rocks_a.html)
If you think of a cookie as a rock, the flour, sugar, and chocolate chips are like the minerals that make up the rock. Depending on the recipe, you get different kinds of cookies. It is the same with rocks because each type of rock has a different combination (or recipe) of minerals.
Minerals all have chemical compositions and physical properties unique to that specific mineral. (A chocolate chip in an oatmeal cookie is the same as the chocolate chip in a peanut butter cookie). Even rocks with the same mineral ingredients may be different due to variations in the amounts of minerals (more flour, fewer chocolate chips) and the processes by which they are formed such as being burned, doughy, or just right. Common rock-forming minerals are feldspar, quartz, calcite, mica, and hornblende. (http://scienceviews.com/geology/rockproperties.html)
To meet the definition of "mineral" used by most geologists, a substance must meet five requirements:
• naturally occurring
• definite chemical composition
• ordered internal structure
"Naturally occurring" means that people did not make it. Steel is not a mineral because it is an alloy produced by people. "Inorganic" means that the substance is not made by an organism. Wood and pearls are made by organisms and thus are not minerals. "Solid" means that it is not a liquid or a gas at standard temperature and pressure.
"Definite chemical composition" means that all occurrences of that mineral have a chemical composition that varies within a specific limited range. For example: the mineral halite (known as "rock salt" when it is mined) has a chemical composition of NaCl. It is made up of an equal number of atoms of sodium and chlorine.
"Ordered internal structure" means that the atoms in a mineral are arranged in a systematic and repeating pattern. The structure of the mineral halite is shown in the illustration on this page. Halite is composed of an equal ratio of sodium and chlorine atoms arranged in a cubic pattern. (http://geology.com/minerals/what-is-a-mineral.shtml)