EAS 100-51: Introduction to Earth Science


Disclaimer: These essay-style questions are a review supplement to (NOT a subtitute for) lecture notes, handouts, and text reading, nor are they considered to be necessarily representative of an actual exam.

1. What are the 3 fundamental sub-atomic particles which make up most atoms?

Protons (+ electrical charge) and neutrons (no electrical charge) reside in the center (nucleus) an atom.  Electrons (negatively charged), which are much smaller particles which whirl at great speed around the nucleus, at different distances (orbitals).  The outermost electrons can transfer from one atom to another during chemical reactions.

2. How do you distinguish between the atomic number vs. the atomic weight of an element?

Atomic Number = # of protons (establishes the identity of an element)
Atomic Weight = # of protons & neutrons

3. What is an ion? How are they produced?

An ion is an electrically unbalanced atom. Normally, the number of electrons equal the number of protons in an atom. If a single electron becomes dislodged, the atom acquires a charge of +1. If an atom gains 2 extra electrons, the atom acquires a charge of -2.

4. What is an isotope? Are all isotopes radioactive?

An isotope is a natural-occurring variety of an element which contains extra neutrons this changes the atomic weight, but does not change the atomic number, such as Carbon 14 ("normal" carbon is Carbon 12), or deuterium ("heavy hydrogen"). Not all isotopes are radioactive (such as Uranium 235); some are called stable isotopes, such as Oxygen 18 ("normal" oxygen is Oxygen 16).

5. What is the most common element in the universe? In what form is this element found on Earth?

Hydrogen is the most common element in the universe, about 70%. Because of its low density, most of the original hydrogen in Earth's early atmosphere was lost to outer space, blown away by the solar wind. Most of the hydrogen on earth is bound up as water, H2O.

6. How did Earth originally form, and what relationship does it have with the Sun and the solar system?

About 4.5 billion years ago, the Earth formed as one of the planets from left over cosmic dust and gas from the formation of the Sun. The planets were spun into orbit by the whirling of the cosmic dust cloud that later became the Sun. The Sun's gravity has kept the planets in orbit ever since.

7. What are the terrestrial planets? What are the gas giants? What explains their different origins within the same solar system?

The terrestrial (Earth-like) planets are relatively small and have rocky cores; they include Mercury, Venus, Earth, and Mars; due to their proximity to the Sun, most of their original hydrogen was blown away by the solar wind, early in the history of the solar system. The gas giants are much larger planets which retained much of their original hydrogen due to their great distance from the sun, and include Jupiter, Saturn, Neptune, and Uranus. (Pluto seems to resemble a terrestrial planet, and is believed to be a moon captured by Neptune's gravity.)

8. How old is the Earth, and how do we know this?

Although the oldest rocks found on Earth are about 3.8 billion years old, the age of the Earth is set at about 4.5 billion years, using radiometric dating to determine the age of meteorites found on Earth. Meteorites are left over material from the formation of the solar system it is assumed that Earth was formed at the same time as the meteorites from common origins.

9. What are the sources of the earth's internal heat?

Earth's internal heat has several sources, accumulated from its earliest history:

  1. heat of accretion (collisions of cosmic dust, meteorites, asteroids, and comets during Earth's earliest history
  2. heat from radioactive decay of elements in the earth's interior
Heat always flows from a hotter place to a cooler place; therefore, the earth's internal heat has been trying to escape ever since the planet formed. This internal heat drives processes such as the movement of the tectonic plates, the formation of magma, volcanism, mountain building, and earthquakes.

10.What is the source of the earth's external heat?

The sun is the source of the earth's external heat, which drives the earth's weather patterns, which in turn affect the surface processes of weathering and erosion.

11. Explain how the earth's processes are in a dynamic equilibrium .

Over geologic time, the earth's internal processes which create new rock (volcanism, mountain-building) are balanced against earth's surface processes which destroy rock (weathering, erosion), as evidenced by the diversity of landscapes that exists.   An erosion-dominated Earth would eventually become completely covered by the oceans, while a mountain-building dominated Earth would eventually become completely mountainous with no flat-lying plains.

12. What is the most common element in the earth's crust? What are the 8 most common elements in the earth's crust? What is the most common element in the earth's interior?

Oxygen is the most common element in the earth's crust. The 8 most common elements (from most to least abudant) in the earth's crust are: O, Si, Al, Fe, Ca, Na, K, and Mg (oxygen, silicon, aluminum, iron, calcium, sodium, potassium, magnesium).  This list does NOT apply to earth as a whole, because the most common element in the earth's interior is iron, which makes up the inner and outer core.

13. What is a chemical compound? How can compounds differ from their constituent elements?

Any combination of 2 or more elements is a compound. Many compounds differ drastically from their constituent elements; for example, sodium chloride is an edible compound, but sodium is a toxic, flammable metal, while chlorine is a poisonous gas.

14. What is a crystalline substance? In contrast, what is a glass, or an amorphous solid?

A crystalline substance is an ordered solid, whose atoms are arranged in an orderly, repeating internal arrangement; a unit of such as substance is called a crystal. A glass is an unordered solid, whose atoms are randomly or chaotically arranged, often due to extremely quick cooling from a molten state. An amorphous solid is simply a solid that has no obvious crystal form.

15. What are the 5 criteria required for a substance to be properly called a mineral ?

  1. Must be naturally occurring
  2. Must be a solid
  3. Must have a definite chemical composition
  4. Must be inorganic
  5. Must have crystalline structure (internal repeating atomic arrangement)
16. Are all chemical compounds also minerals? Are minerals all chemical compounds?

No, there are many chemical compounds which do not fit the above criteria for minerals, including those which are man made, liquid or gas, organic, or have no crystalline structure. It is possible for a mineral to be composed of just a single element; for example, graphite (carbon) or native copper.  Ice and snow are minerals; osidian, man-made glass, and sugar are not minerals.

17. What group of minerals are the most common? Why are they called rock-forming minerals ? What is the basic unit among rock forming minerals?

The most common minerals are the silicates, which are called rock forming minerals because they make up most of the rocks found in the earth's crust. The silica tetrahedron (SiO4) forms the basic unit or building block of the rock forming minerals.

18. How are the earth's elements distributed, in a homogeneous (evenly-distributed) fashion, or in a heterogeneous (unevenly distributed) fashion? How did this distribution come about?

Earth's elements are unevenly distributed; most of the lighter elements are found in the earth's crust, while the heavier elements (including most of the iron) are found in the earth's core and mantle. Within the first half billion years of the young earth's history, the internal heat of the earth and/or intense meteorite bombardment re-melted and destroyed the original crust and caused a catastrophic redistribution of the elements (termed the "Great Iron Catastrophe").

19. How is a rock distinguished from a mineral? Do all rocks contain minerals?

A rock is defined as an aggregate or combination of minerals; these minerals still retain all their original properties. Most, but not all rocks contain minerals exceptions would include obsidian (volcanic glass) and coal (organic material).

20. How do igneous rocks form? What distinguishes a magma from a lava ?

Igneous rocks form from the cooling (crystallization) of molten material called magma, which originates in the earth's mantle by partial melting. Magma which escapes to the surface loses its volatile gas components, and is then called lava .

21. Why are igneous rocks sometimes called crystalline rock? What is the typical texture of an igneous rock?

Igneous rocks are typically composed of interlocking crystals of silicate minerals; the minerals have sharp, angular crystals and there is no void space between crystals.

22. What effect does the rate of cooling have on an igneous rock? How can you determine the cooling history of an igneous rock?

A slow rate of cooling allows coarse (visible to the naked eye) crystals to form; this requires a magma cooling at great depth in the earth's interior, where heat escapes very slowly.

A fast rate of cooling allows fine crystals to form; this requires cooling of a lava at or near the earth's surface, where heat escapes rapidly.

An extremely fast rate of cooling allows no crystals to form; this results from cooling of lava or volcanic material by seawater or the air; this material then becomes a volcanic glass .

23. What is meant by a porphyritic texture? How can you explain this in terms of the cooling history that produced it?

A porphyritic texture means a mostly fine-grained igneous rock that shows "oddball" crystals that are conspicuously coarser (called phenocrysts ). This indicates a 2 stage cooling history; the phenocrysts formed at depth, but before the magma could completely crystallize, it erupted to the surface, where the surrounding fine crystals (collectively called the groundmass) formed.

24. What is Bowen's Reaction series, and what class of rocks does it apply to?

Geologist Norman Bowen determined the sequences of silicate minerals which crystallize out of a cooling basaltic magma to include: olivine, pyroxene, amphibole, biotite, feldspar, and quartz. The plagioclase feldspars also form a continuously variable sequence that changes from a calcium-rich to sodium-rich as the temperature of the magma cools. Bowen's Reaction Series applies to igneous rocks only.

25. What is meant by the terms felsic, mafic, and intermediate ? Name examples of each type.

Felsic describes igneous rocks composed of mostly potassium fel dspar and si lica (quartz), such as granite or rhyolite.  Mafic (or ferromagnesian ) describes igneous rocks composed mostly of mineral high in iron and magnesium, such as gabbro or basalt . Intermediate igneous rocks are composed mainly of plagioclase feldspar and amphibole, and are often made by a mixture of felsic and mafic magmas in zones where tectonic plates of different mineral composition collide; examples include andesite and diorite .

26. What is meant by plutonic (intrusive) and volcanic (extrusive)? Name an example of each type.

Plutonic or intrusive igneous rocks cool slowly at great depth; examples: granite, gabbro. Volcanic or extrusive igneous rocks cool quickly at or near the earth's surface; examples: rhyolite, basalt.

27.  How are weathering and erosion distinguished from each other?

Weathering is the disintegration and decomposition of rock at or near the earth's surface. Erosion is the incorporation and transportation of rock material by a mobile agent, such as water, wind, or ice (glacier). Both of these processes usually occur together.

28.  How is physical weathering distinguished from chemical weathering ?

Physical weathering involves mainly change in shape (rounding) and grain size (reduction). Chemical weathering involves changes in the chemical composition of the minerals in a rock to a more stable composition.

29.  What are the agents of weathering and erosion?

  1. Water (erode and transport sediments; chemical weathering)
  2. Wind (erodes and transport lightweight sediments)
  3. Ice (glaciers move sediments and rocks)
  4. Sun (daily freeze-thawing cycles eventually cracks rocks)
  5. Plants (roots enlarge cracks)
30. What minerals tend to be unstable under chemical weathering?

The mafic minerals which crystallized at higher temperatures, such as olivine and pyroxene, tend to chemically weather rapidly at the earth's surface, changing to serpentine and then to clay minerals.

31. Why do rocks and minerals undergo weathering?

Rocks and minerals undergo weathering in response to changes in its environment which may be different than its original environment of formation.

32. What process turns sediments into sedimentary rock?

Loose, unconsolidated sediments may accumulate in thick deposits whose overlying weight causes compression of the original void space between the grains; later, groundwater containing dissolved minerals such as silica or calcium carbonate may precipitate as mineral cement between the grains, thereby creating a sedimentary rock. This process is called lithification.

33. How does the typical appearance of a sedimentary rock indicate the surface processes that produced it?

Surface processes reflect a low temperature, low pressure environment, and the effects of water, wind, ice, and/or sun. Rounding, stratification (bedding), and fossils found in sedimentary rocks all indicate surface processes.

34. What is a clastic sedimentary rock? What is the most common clastic rock?

Rocks made from broken pieces of pre existing rock are called clastic . The most common clastic sedimentary rock is shale, which is made up of fine grained clay minerals weathered from mafic minerals and feldspars.

35. What is a chemical sedimentary rock? What is the most common chemical sedimentary rock?

Rocks made up of chemical precipitates (minerals crystallized in water from a dissolved state) are classified as chemical sedimentary rocks; the most common example are limestones, which are usually a mixture of calcium carbonate fossil seashells held together with precipitated calcium carbonate cement. Coal is also classified as a chemical sedimentary rock, although it is composed of organic material rather than minerals.

36. What is carbonic acid ? How is it formed and what role does it play in chemical weathering? How does it affect surface outcrops of limestone?

Carbonic acid is a weak, naturally occurring acid made from carbon dioxide dissolved in rainwater. This weak acid is responsible for chemical weathering of minerals; some minerals weather more quickly than others for example, calcite and olivine weather much more quickly than quartz. Because calcite is the major mineral that makes up most limestones, landscapes in humid climates which feature outcrops of limestone bedrock are transformed into karst topography the formation of caves, sinkholes, and solution cavities.

37. What is meant by a well-sorted sediment? What is meant by a poorly-sorted sediment? Name rock examples of each type.

A well-sorted sediment has a uniform overall grain size (all sediment grains are about the same size); examples include quartz sandstones and shales. A poorly-sorted sediment has a diverse range of grain sizes; examples include conglomerate and breccia.

38. What information do coarse, angular sediments provide about their origin?

Coarse, angular sediments indicate deposition near the source rock, because further transport of sediment tends to produce finer, rounder sediments.

39. What are fossils, and in what types of rocks are they found?

Fossils are the remains or traces of ancient animals and plants. Because living organisms are indicative of the surface environment, fossils are found almost exclusively in sedimentary rocks.

40. Why do sedimentary rocks tend to be deposited in flat, horizontal beds?

Sediments are deposited in response to gravity, which produces flat, horizontal beds.

41. What explains the abundance of shales?

Shales are made up of clay minerals, which have a wide variety of sources, including most of the mafic minerals and feldspars. (By contrast, the quartz found in sandstones has only one source, the quartz in the source rock.) For this reason, shale is the most abundant sedimentary rock.

42. What does the concept of the rock cycle demonstrate?

The rock cycle demonstrates that rocks do not last forever, and any pre-existing rock may be transformed into another over geologic time, reflecting changes in temperature and pressure.

43. What are the primary agents of metamorphism?

  1. Heat (usually under 200oC., which is not enough to produce complete melting)
  2. Pressure (low to high)
  3. Chemically-active fluids (hot groundwater, which helps to move atoms in recrystallizing minerals)
Heat and pressure changes usually occur together to produce metamorphic rocks; chemically active fluids, if present, aid the process, but are not absolutely necessary.

44. Distinguish between contact metamorphism and regional metamorphism.

Contact metamorphism is heat-dominated , whereby a magma body intrudes an overlying rock and produces a localized "baked" zone where new minerals are recrystallized by the heat of the magma. Regional metamorphism is pressure-dominated , where pressures produced by moving tectonic plates may bend, fold, warp, distort, or break large slabs of rock over a very large area.

45. What is foliation ? Name several examples of foliated rocks. Name several examples of non foliated rocks.

Foliation is a texture seen in metamorphic rocks whereby elongated or platy (mica-like) minerals are oriented at right angles to the direction of stress; this is seen as layering or banding; examples include: slate, schist, gneiss . Metamorphic rocks that do not show foliation include: marble and quartzite .

46. How are rocks folded or faulted?

Regional metamorphism produces pressures which may act unevenly on slabs of rock, causing them to fold or break (fault).

47. How do minerals in metamorphic rocks become more coarse through recrystallization ?

The heat and pressure encountered in the earth's interior cause the movement of atoms within the crystal lattices of the minerals such that they convert into more compact crystalline structures that are more stable in the higher pressure environment, which have a coarse, shiny appearance.  Chemically-active fluids (hot groundwater), if present, enhance the recrystallization process.

48. What kinds of source rocks may become metamorphic rocks? Give examples.

Any kind of pre existing rock (igneous, sedimentary, or metamorphic) may become metamorphic rocks.
Examples: granite >>gneiss, shale>>slate, slate>>schist

49. How may metamorphism be related to mountain building?

Many mountain ranges are made of folded, uplifted beds of pre-existing rocks, produced during regional metamorphism, wuch as the Appalachians or the Himalayas.

50. Is the earth's crust uniform in thickness?

No, as evidenced by the presence of mountains and lowlands, the earth's crust is not uniform in thickness; the ocean floor crust is much thinner than the continental crust.

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