1. Weathering and erosion, the processes which break down and destroy rocks, have removed portions of the rock record. Also, there are periods of geological time where no rock record was made, as most sedimentary rocks are deposited in marine environments. MAKE SURE YOU DONT USE UNLOCK
2. Igneous rocks are formed from the cooling and crystallization of molten rock called magma . The size of the crystals are governed by the rate of cooling; hence, an igneous rock at or near the earth's surface cools more quickly, and the size of crystals is fine-grained . Rocks which cool deep below the ground cool more slowly and thus have a coarse crystal size.

3. Sedimentary rocks are formed at the Earth's surface. Weathering and erosion produce fragments of broken rock, creating a subclass of sedimentary rocks known as clastics, of which shales are most common. The most common chemical sedimentary rocks are limestones which are usually made up of the accumulated calcium carbonate shells of dead sea animals.

4. Clastic sedimentary rocks are made from the weathering of parent rocks, which are most commonly made of rock-forming silicate minerals. Of the common silicate minerals, most of the mafics (olivine, pyroxene, amphibole, plagioclase, K-feldspar, micas) weather into clay minerals, which form shales.

5. Metamorphic rocks are changed by heat and pressure (usually a combination of both). Contact metamorphism is dominated by heat, usually the result of an igneous intrusion coming in contact and locally "baking" the overlying rock. Regional metamorphism is dominated by pressure, causing folding, warping, and faulting of rocks.

6. The basic components of a soil are: mineral, gas (air), liquid (water), and organic matter. In general, more organic matter makes a richer, darker-colored soil, because it holds more soil nutrients than soils with less organic matter.

7. In tropical climates, physical and chemical weathering are very severe - even clay minerals do not survive under these conditions. Clays weather into non-crystalline substances called allophanes which hold few or no soil nutrients; they are usually a rusty red (from oxidized iron) color. The soil sustains plant growth through the production of humus (an organic substance produced by soil microbes) in the warm, humid climate, and by increased diversity (increasing the variety of different species of plants and animals. In other words, "there is a little of everything, but not a lot of any one thing" in the jungle. This means that the limited food supply can be spread out amongst many different living things that compete for a different mix of nutrients. On the other hand, modern agriculture is based upon growing a lot of one crop; something which a jungle soil cannot support.

8. Earth's water originally came from the mantle rock of the interior, and from comets during the period of early bombardment (4.6 to 3.9 billion years ago). Silicate minerals such as amphiboles contain water in their crystal structures, and during an early period (over 3 billion years ago) of intense volcanism, tremendous clouds of steam boiled out with the lava. As the hot, young Earth slowly cooled, the steam eventually condensed into liquid water, and the cycle of rain and evaporation began. The rain may have lasted for thousands of years, in order to fill the ocean basins of today.

9. 71% of the Earth is covered by water. However, since most of this water is salty ocean water, we cannot economically use it without expensive salt-removal methods.

10. Geologically-young streams are born in a hilly or mountainous area; the steep slope provides enough gravitational energy to make the water run fast. As long as the stream moves fast, it has enough downward-cutting force to erode a V-shaped stream valley. As the slope levels off downstream, the speed of the stream water slows down, and the stream has less power to erode the bottom of the streambed or carry sediments. So, the mature or old stream meanders (zig-zags), floods, and creates a floodplain.

11. Sediments deposit by gravity. Clastic sediments are carried (suspended) by air or water only as long as there is enough energy to move them. As soon as the air or water slows down, sediment gets dumped (deposited). Rivers are forced to slow down whenever they meet a wider body of water, such as a lake or ocean. When a river meets the ocean, the sediment that it carried gets dumped in a fan-shaped deposit called a delta. Lake sediments are usually fine-grained because the water is very calm; when a stream nears a lake, its water slows down enough to dump the coarser, heavier sediment upstream, so not much coarse sediment makes it into the lake bottom.

12. Porosity is the percentage of void (pore) space in a rock, by volume. Permeability is a measure of a rock's ability to permit water to move through it, and is usually numerically expressed as a rate. Permeability depends upon inter-connected pore space. Even a very porous rock may be relatively impermeable, if the pore spaces are not inter-connected. An aquifer is a permeable rock which holds and releases water in good quantities. An aquitard is a relatively impermeable rock which acts as a barrier to the passage of water. An aquiclude is a very impermeable rock.

13. Examples of good aquifers: well-sorted sandstones, conglomerates, glacial sediments, fractured limestones, dolomites, or igneous rocks. Shales, and unfractured igneous rocks, limestones, or marbles are not good candidates for aquifers.

14. An artesian well is an aquifer which is under pressure; the pressure is created by a elevated recharge area and a cap rock above and below the aquifer; the water rises at the well without pumping. A perched water table is created by a small amount of cap rock below part of the aquifer; it raises the water table to an unusually high elevation in that local area.

15. Pumping out water faster than it can naturally recharge will lower the water table. In some instances, the water table may sink into deeply-buried aquifers containing ancient sea water, which will contaminate the wells with salt.

16. Far below the Niagaran (Silurian-age) dolomite bedrock of Chicago, is a much older, very thick (thousands of feet) Cambrian-age, permeable rock formation called the Mt. Simon Sandstone. Its lateral extent is also very broad, it slopes toward the surface going northward, so that it can be seen as rock outcrops in Wisconsin, known as the Wisconsin Dells.

17. Chicago's bedrock dates back to the Silurian Period, which was about 420 million years ago. Almost directly above this rock are much younger deposits left by the glaciers some 11,000 years ago. So, there is a 400 million year gap. This gap in the rock record is explained by: erosion and/or lack of deposition.

18. Lake Chicago was an extension of Lake Michigan, created during the last Ice Age, about 13,000 years ago. Water melting from the glaciers provided the extra lake volume. The lake rose to about 640' above sea level at its highest stage, and sank to 230' above sea level at its lowest stage, a difference of over 400 feet.

19. The landscape of Chicago is unusually flat for several reasons. First, the last glacial advance (11,000 years ago) scraped the bedrock smooth. Second, the periodic melting of the glacial ice enlarged the lake; wave action in the shallow lake cut the bedrock bottom smooth.

20. The Earth's climate may cool during a period of intense volcanic activity, where large amounts of ash and dust belched into the upper atmosphere blocks enough incoming sunlight to cause cooler temperatures for a prolonged period. Under this scenario, more snowfall means more glacial ice, and a world-wide drop in sea level. A scenario for a warming effect on Earth's climate: An increase in the amount of carbon dioxide gas in the atmosphere (which results from the large-scale burning of fossil fuels) may aggravate the greenhouse effect, allowing more of the sun's radiant energy to be trapped at the surface. Under this scenario, higher temperatures would melt more of the glacial ice, causing a rise in sea level, flooding many coastal cities, where most of the world's people live today.

21. Snow, when packed into a thick, heavy mass, will recrystallize first into a more compact, harder, transitional substance between snow and ice, called firn, then crystallize into ice. Thus, the glaciers were made from snow which eventually turned into ice.

22. When a ice sheet reaches 50 meters thick, the overlying weight causes plastic deformation of (non-reversible change in shape) ice, and the ice sheet begins to flow downhill, like a thick mass of slush.

23. A world-wide warming of the climate would produce sweltering summer heat, drought, crop failures, higher electric bills, and eventually, flooding of coastal areas as the polar icecaps melt and sea level rises.

24. A world-wide cooling of the climate would produce record-cold winters, shorter growing seasons, increase in the consumption of heating fuels, and eventually, a lowering of sea level.

25. Glacial deposits usually consist of poorly-sorted, unstratified (uncemented) sediments. Most of the sand and gravel used by the construction industry is quarried from glacial deposits.

26. The uneven heating of the Earth caused by irregularities in the topography of the land creates the winds. The distribution, direction, and magnitude of winds is further influenced by the interaction between the atmosphere and the oceans (hurricanes are an extreme example).

27. Stalactites are icicle-like pendants that form on the ceiling of a cavern and grow downward, whereas stalagmites grow upwards from the cavern floor. These features form when water rich in dissolved calcium carbonate reaches the cavern. At this point, some of the carbon dioxide in solution escapes, causing calcite to be deposited.

28. About 30% of the Earth's surface is now covered by arid and semi-arid regions.

29. Wind is relatively more effective in dry regions because the lack of moisture to bind soil particles together, and because sparse vegetation does not hold soil in place as the more widespread vegetation in humid climates.

30. Sand dunes migrate when sand grains are rolled and saltated by blowing wind up the more gently sloping windward side until they reach the crest of the dune, where they tumble down the steeper leeward side.