Rock Cycle and Rock Clues
A rock has large visible crystals and no layers. What does this tell you about how it formed?
It is most likely an intrusive igneous rock. Large visible crystals usually mean the rock cooled slowly underground from magma.
Why is Georgia’s Piedmont mostly made of metamorphic rocks like gneiss and schist?
The Piedmont has been affected by ancient tectonic collisions, especially during the formation of Pangaea and the Appalachian Mountains. Those collisions created heat and pressure that changed older rocks into metamorphic rocks such as gneiss and schist.
A plate boundary has a mid-ocean ridge, shallow earthquakes, and new crust forming. Identify the boundary.
It is a divergent boundary. The evidence is that plates are moving apart, magma rises, new oceanic crust forms, and earthquakes are shallow near the surface.
The temperature is 63°F and the dew point is 62°F. What does this suggest about the air and possible cloud or fog formation?
The air is nearly saturated because the temperature and dew point are very close. Clouds or fog are more likely because the air does not need to cool much for condensation to occur.
A student says, “Climate is the weather today.” Explain why this is incorrect.
Weather is short-term atmospheric conditions, such as today’s temperature or rain. Climate is the long-term pattern of weather in a place, such as Georgia having hot, humid summers.
A rock has vesicles and a fine-grained texture. What type of rock is it most likely to be, and what caused the vesicles?
It is most likely an extrusive igneous rock, such as basalt. Vesicles formed when gas bubbles were trapped in lava as it cooled quickly at Earth’s surface.
Explain how red clay forms in Georgia. Include chemical weathering and iron oxidation.
Georgia’s red clay forms through chemical weathering. Minerals in rocks break down over long periods of time. Iron-rich minerals react with oxygen, or oxidize, which gives the clay its red color.
A coastline has an offshore trench, inland volcanoes, and earthquakes that get deeper inland. Identify the boundary and explain what is happening.
It is an oceanic-continental convergent boundary. The denser oceanic plate is subducting beneath the continental plate. The trench forms where the oceanic plate bends downward, volcanoes form inland, and earthquake depth increases as the plate sinks deeper.
Explain why air rising over a mountain can lead to clouds or precipitation.
As air rises over a mountain, it expands and cools. If it cools to the dew point, water vapor condenses into cloud droplets or ice crystals. This can produce clouds and precipitation.
Why are coastal cities usually less extreme in temperature than inland cities?
Water heats and cools more slowly than land. Coastal areas near oceans have moderated temperatures, so they usually do not get as hot in summer or as cold in winter as inland areas.
A rock contains visible fossils and forms in layers. What type of rock is it most likely to be, and why are fossils more common in this rock type?
It is most likely sedimentary rock. Sedimentary rocks often form in layers from deposited sediments, and fossils are more likely to be preserved because the rock forms at lower temperatures and pressures than igneous or metamorphic rocks.
How could quartz grains from the Appalachian Mountains eventually become sand on a Florida beach?
Quartz in the Appalachian Mountains can be broken loose by weathering. Erosion and rivers can transport the quartz grains. The grains can be deposited and moved farther downstream toward the Coastal Plain and eventually to Florida beaches.
Compare a trench and a mid-ocean ridge. Include the boundary type and whether crust is created or destroyed.
A trench forms at a convergent boundary where subduction destroys or recycles crust. A mid-ocean ridge forms at a divergent boundary where seafloor spreading creates new oceanic crust.
Compare a cold front and a warm front. Include how the warm air rises and what kind of weather each often brings.
A cold front happens when cold air moves into a warm area and forces warm air upward quickly. This can cause heavy rain or thunderstorms, followed by cooler and drier air. A warm front happens when warm air rises slowly over cooler air, often causing widespread clouds and steady light rain.
Explain why summer in the Northern Hemisphere is not caused by Earth being closer to the Sun.
Summer is caused by Earth’s axial tilt, not distance from the Sun. During Northern Hemisphere summer, the Northern Hemisphere is tilted toward the Sun, sunlight is more direct, the Sun appears higher in the sky, and days are longer.
Sandstone is changed into quartzite. What process caused this change, and why did the rock not become igneous?
Heat and pressure changed sandstone into quartzite, so it became metamorphic. It did not become igneous because it did not melt and then cool.
Why did the formation of Pangaea affect Georgia’s geology?
The formation of Pangaea involved ancient continental collisions. Those collisions helped form the Appalachian Mountains and changed rocks in Georgia through heat and pressure, producing many metamorphic rocks in the Piedmont.
Wegener had evidence that continents moved, but his original idea was incomplete. What evidence supported him, and what was missing?
Evidence included matching fossils across continents, matching rock layers and mountain ranges, the fit of continents, and past climate evidence such as glacial deposits. His idea was incomplete because he could not explain what force moved the continents.
A student says, “If the air is humid, clouds must form.” Explain why this is not always true.
Humidity means the air contains water vapor, but clouds form when air cools enough for condensation. If the temperature is not close to the dew point, the air may still be humid without forming clouds.
What conditions can help tornadoes form, and how is a supercell different from a regular thunderstorm?
Tornadoes can form when warm, moist air is near the ground, cooler air is above, wind shear is present, and there is a lifting trigger such as a front. A supercell is different because it has a rotating updraft.
Put these rock cycle events in a logical order to form a sedimentary rock from an existing mountain rock:
erosion, compaction, deposition, weathering, cementation.
Explain each step briefly.
Weathering breaks the mountain rock into sediment.
Erosion moves the sediment.
Deposition drops the sediment in a new location.
Compaction squeezes the sediment together.
Cementation glues the sediment together to form sedimentary rock.
A student finds a shiny mineral that breaks along flat surfaces. What two mineral properties are being described, and how could those properties help identify the mineral?
The shiny appearance describes luster. Breaking along flat surfaces describes cleavage. These properties help identify a mineral because different minerals reflect light and break in different ways.
A volcanic island chain has the youngest island at one end and older islands farther away. What does this show?
A hotspot chain shows plate movement. The youngest volcano is usually closest to the hotspot, while older volcanoes are farther away because the tectonic plate moved over the stationary or mostly stationary hotspot.
A strong thunderstorm forms along a cold front. Explain the chain of events from the cold air arriving to the storm forming.
Cold air moves into a warm area and pushes under the warm air. The warm, moist air rises quickly. As it rises, it expands and cools. Water vapor condenses to form clouds, and strong rising air can help produce thunderstorms.
Moist air crosses a mountain range and creates a dry area on the other side. Explain the full rain shadow process from windward side to leeward side.
Moist air rises on the windward side of a mountain. As it rises, it cools and water vapor condenses, causing clouds or precipitation. After crossing the mountain, the air has lost much of its moisture. It sinks on the leeward side, warms, and becomes drier, creating a rain shadow.