AP Environmental Science:: Unit 4 - Earthsystems

Earth's atmosphere is structured into several distinct vertical layers based primarily on changes in temperature with altitude. The lowest atmospheric layer, where essentially all of Earth's weather occurs, is called the:

- **A)** Troposphere, which extends from Earth's surface up to roughly 10-15 km altitude and contains roughly 75-80% of the atmosphere's total mass, along with essentially all of the water vapor responsible for weather phenomena
- **B)** Stratosphere, which instead lies directly above the troposphere and contains the protective ozone layer, rather than being the layer where weather itself occurs
- **C)** Mesosphere, a much higher atmospheric layer where meteors typically burn up, well above where weather-producing water vapor is concentrated
- **D)** Thermosphere, the outermost major atmospheric layer, where incoming solar radiation is absorbed at extremely high altitude, well above where weather occurs

The stratosphere, the atmospheric layer directly above the troposphere, is of particular environmental significance primarily because it contains:

- **A)** Essentially all of Earth's weather-producing water vapor, a description that instead corresponds to the troposphere (discussed above), not the stratosphere specifically
- **B)** The single highest concentration of atmospheric carbon dioxide of any atmospheric layer
- **C)** The ozone layer, a naturally-occurring concentration of ozone (O3) molecules that absorbs the great majority of the sun's harmful ultraviolet (UV) radiation before it can reach Earth's surface - protecting living organisms from UV-related harm such as skin cancer, cataracts, and damage to many species' DNA
- **D)** No meaningful concentration of any atmospheric gas relevant to environmental science

Earth's atmosphere is composed overwhelmingly of two gases, which together make up roughly 99% of its total volume. These two dominant gases are:

- **A)** Oxygen and carbon dioxide, which together make up only a small fraction of the atmosphere's total volume, not the roughly 99% majority actually held by the two truly dominant gases
- **B)** Nitrogen (roughly 78% of atmospheric volume) and oxygen (roughly 21% of atmospheric volume) - the remaining roughly 1% consists of argon, carbon dioxide, and a variety of other trace gases, several of which (including carbon dioxide, methane, and water vapor) play a disproportionately large role in the greenhouse effect discussed further below despite their comparatively very small atmospheric concentration
- **C)** Hydrogen and helium, which are in fact only present in trace, essentially negligible amounts within Earth's own atmosphere
- **D)** Ozone and argon, neither of which makes up anywhere close to a dominant proportion of atmospheric volume

The natural greenhouse effect, a fundamentally important and naturally-occurring atmospheric process (distinct from human-caused climate change, covered in a later unit), works by:

- **A)** Reflecting all incoming solar radiation directly back into space before it can ever reach Earth's surface at all, preventing the surface from warming to any meaningful degree
- **B)** Cooling Earth's surface well below the temperature it would otherwise reach in the complete absence of any atmosphere at all
- **C)** A process that has no meaningful, describable relationship to solar radiation, atmospheric gases, or surface temperature of any kind
- **D)** Allowing incoming shorter-wavelength solar radiation to pass through the atmosphere and warm Earth's surface, while certain atmospheric gases (greenhouse gases, such as carbon dioxide, methane, and water vapor) then absorb and re-radiate a substantial portion of the resulting longer-wavelength infrared radiation that Earth's surface itself emits back outward, trapping additional heat within the lower atmosphere - without this natural greenhouse effect, Earth's average surface temperature would be far too cold to support life as it exists today

Earth's rock cycle describes the ongoing transformation of rock material between three fundamental rock types: igneous, sedimentary, and metamorphic. Igneous rock specifically forms when:

- **A)** Molten rock material (magma below the surface, or lava once it reaches the surface) cools and solidifies/crystallizes - igneous rock that cools slowly underground (such as granite) typically develops larger, more visible mineral crystals than igneous rock that cools rapidly at the surface (such as basalt), which typically has much smaller, less visible crystals
- **B)** Pre-existing rock material is subjected to intense heat and/or pressure (without fully melting), causing its mineral structure to physically change/recrystallize, a description that instead corresponds to metamorphic rock formation, not igneous rock formation specifically
- **C)** Sediment particles (eroded fragments of pre-existing rock, or accumulated organic/mineral material) are compacted and cemented together over time, a description that instead corresponds to sedimentary rock formation, not igneous rock formation specifically
- **D)** A rock type that has no meaningful, describable relationship to magma, lava, cooling, or crystallization of any kind

Sedimentary rock, one of the three fundamental rock types in the rock cycle, forms primarily through the process of:

- **A)** Molten rock material cooling and solidifying, a description that instead corresponds to igneous rock formation (discussed above), not sedimentary rock formation specifically
- **B)** Pre-existing rock being subjected to intense heat and/or pressure without fully melting, a description that instead corresponds to metamorphic rock formation (discussed below), not sedimentary rock formation specifically
- **C)** Weathering and erosion breaking down pre-existing rock into smaller sediment particles, which are then transported (typically by water, wind, or ice), deposited in layers, and eventually compacted and cemented together over a long period of time - sedimentary rock frequently contains fossils, since the same gradual, low-temperature deposition process that forms the rock itself can also preserve the remains of organisms buried within its accumulating sediment layers
- **D)** A rock type that has no meaningful, describable relationship to weathering, erosion, sediment, or deposition of any kind

Metamorphic rock, the third fundamental rock type in the rock cycle, forms when:

- **A)** Sediment particles are compacted and cemented together over time, a description that instead corresponds to sedimentary rock formation (discussed above), not metamorphic rock formation specifically
- **B)** Pre-existing rock (of any of the three fundamental rock types, including previously-formed metamorphic rock itself) is subjected to intense heat and/or pressure deep within Earth's crust, without fully melting into magma - this heat/pressure causes the rock's original mineral structure to physically change/recrystallize into a new, typically denser and more tightly-layered or "foliated" rock structure, without the material ever having actually melted in the process
- **C)** Molten rock material cools and solidifies at Earth's surface, a description that instead corresponds to igneous rock formation (discussed above), not metamorphic rock formation specifically
- **D)** A rock type that has no meaningful, describable relationship to heat, pressure, or mineral recrystallization of any kind

Plate tectonics, the scientific theory describing the large-scale movement of Earth's rigid outer crust (divided into large tectonic plates), explains geological phenomena such as earthquakes, volcanic activity, and mountain formation as resulting primarily from:

- **A)** Random, entirely unpredictable geological events with no meaningful, describable underlying cause or pattern of any kind
- **B)** Changes in atmospheric temperature and pressure alone, with no meaningful role for any process occurring beneath Earth's own surface
- **C)** The rock cycle discussed above operating in complete isolation, with no meaningful additional role for any large-scale crustal plate movement
- **D)** The slow, ongoing movement of Earth's tectonic plates relative to one another, driven by convection currents in the underlying mantle - plate boundaries where plates collide (convergent boundaries), pull apart (divergent boundaries), or slide past one another (transform boundaries) are each associated with characteristic, distinctive patterns of earthquake activity, volcanic activity, and/or mountain-building, depending on the specific type of boundary and the specific types of plates involved (oceanic versus continental)