Final Exam Flashcards
What is the area of exchange between a river and groundwater called?
hyporheic zone
The distinction between a valley and canyon is…
that the sides of a canyon are more steep than those of a valley
What variables are considered when calculating discharge?
cross-sectional area and velocity
The deepest, fastest channel in a river is called the…
thalweg
What factor affects the rate of downcutting in a river?
rate of uplift, bedrock composition, stream gradient
Most lateral erosion occurs along what part of a meandering river channel?
the cut bank
The base level of a tributary would ____ if a dam and a reservoir were constructed where it flowed into a truncated stream
rise
In uniform sediments with a relatively constant and gentle slop at the surface, a ____ drainage network is expected
trellis
All else being equal, water will flow faster in a stream with ____ and a ____ wetted perimeter
straight channel; small
Which of the following scenarios is more likely to cause a flash flood than a slow-onset flood?
the failure of a stream channel’s levees
A stream carrying sediment flows over the solid rock of its channel, polishing the rock and wearing it away. This is an example of…
abrasion
The stream gradient of most rivers…
is greater near the source than near the mouth
Ultimately, the base level of a stream valley cannot be lower than…
sea level
What physical property of the underlying rock would lead to the formation of a cliff over which a waterfall may form?
a high resistance to erosion
The shape of a delta is primarily determined by…
whether river currents or ocean currents are locally predominant
Within a meander, where is sediment most likely to be deposited?
on the inner banks of the meander
Which of the following is NOT true? A 100-year flood…
cannot occur in successive years
Which of the following IS true? A 100-year flood…
has a 1% chance of occurring in any given year; is more destructive than a 50-year flood; is based on the average recurrence interval of past floods for a particular stream
In some cases, the push of flowing water can break chunks of solid rock off of the channel bed. These pieces are then carried along by a stream as…
bedload
Pirate streams…
form when headward erosion causes one stream to intersect another
Urbanization of a watershed is most likely to result in…
an increase in the volume of water entering streams after rainfall
Which type of aquifer is least likely to be contaminated by surface pollution?
confined aquifer
Darcy’s Law takes into consideration what variables?
discharge, hydraulic gradient, hydraulic conductivity, and cross-sectional area
For several generations, your family have lived on a farm with a water well. There has never been a problem with the water supply in the past; however, your well has now gone dry. There are several small farms nearby and a large, growing city 50 miles to the north. What can you conclude is the most likely reason for your well to become dry?
as the city grew larger, more wells were drilled and water was over-pumped, thus lowering the water table
Karst topography forms predominately in what kind of rock?
limestone
Ultimately geysers erupt because of the…
decrease in pressure as water rises, allowing it to flash to steam
When the ground surface drops below the potentiometric surface, what is formed?
an artesian well
What conditions would lead to the fastest relative groundwater velocity?
high hydraulic gradient and high permeability
You have a choice to drill your water into a shallower unconfined aquifer or a deeper confined aquifer; deeper will cost more money; however, you choose to drill into the confined aquifer. Why?
the confined aquifer will most likely have a higher water quality
The porosity of vesicular basalt is about 25%; however, when water is poured on it, the water does not reach the other side. How is this possible?
the vesicles in basalt are not connected, so it has not permeability
A person is digging a hole, when the hole suddenly starts to fill with water. What have they found?
the water table
Which of the following lists correctly orders the three types of subsurface water from shallowest to deepest?
soil moisture, vadose zone water, groundwater
Rock or sediment between the water table and the land surface represents a(n)…
unsaturated zone
You are drilling a water well when you hit water at a much shallower level than you expected. What have you found?
a perched aquifer
As a rule, groundwater always flows from areas of…
greater hydraulic head to those of lesser hydraulic head
The rate of groundwater flow per unit area through a body of rock or sediment depends on…
the slope of the water table and the permeability of the rock or sediment
Rates of groundwater flow are ____ than stream flow because the water ____
lower; must make its way through tiny pore spaces
You are testing the groundwater quality of an aquifer and find that it has high amounts of arsenic. What is the likely source?
the arsenic comes from dissolved minerals in the aquifer rock
You have a choice to drill you water well into a shallow unconfined aquifer or a deeper artesian aquifer. Drilling deeper will cost more money; nevertheless, you chose to drill into the artesian aquifer. Why?
the artesian aquifer will flow on its own, without a pump
Hot springs can be formed by the heating of groundwater by magma or by…
the geothermal gradient
Imagine that some of the wells around a city have begun to show elevated levels of a toxic substance. Without knowing what the toxic substance is, how can you determine what the source of the chemicals might be?
determine which wells show the chemicals and which do not and use that data to track the flow of the water
Why is a spring tide so much higher than a normal high tide?
because the Sun is aligned with the moon
Which of the following is the BEST example of an organic coast?
shallow coral reef
Which of the following features is a characteristic of a rocky coast?
sea stacks
Barrier islands are constantly moving in the direction of…
the longshore drift
A(n) ____ is a vegetation, flat-lying stretch of coast that floods at high tide, becomes particularly exposed at low tide, and does not feel the impact of strong waves.
coastal wetland
Because of wave refraction, erosion along an irregular coastline is…
greatest along headlands
When sea level rises, an ocean may invade a river valley, producing a nearshore body of water of mixed and variable salinity termed a(n)…
estuary
A coral reef would MOST likely be found…
in the shallow waters surrounding a tropical volcanic island
The Florida coast is an example of a(n)…
submergent coast
Structure - like jetties, groins, and breakwaters - that are designed to prevent beach erosion…
are a temporary solution that decreases the rate of beach erosion
What is the ecosphere?
thin layer of the surface of Earth that interacts with the atmosphere, hydrosphere, and lithosphere; thin layer where life is possible; natural surface system of Earth; from bottom of ocean to mountain peaks and upper limits of lower part of atmosphere; 25 km thick; all life on Earth; only place in solar system that supports life; includes biosphere; biological and physical components of the planet
What is the biosphere?
independent biosphere of living organisms or biological processes at the interface between the atmosphere, lithosphere, and hydrolosphere; holistic view of the Earth, recognizing several interrelated envelopes surrounding a core and mantle; part of world in which life can exist
What is Gaia?
weak Gaia: life wields a substantial influence over some features of the abiotic world, notably the temperature and composition of the atmosphere; Earth’s climate and surface environment are actively regulated by animals, plants, and microorganisms
strong Gaia: Earth is a superorganism which controls the terrestrial environment to suit its own ends, whatever they might be
What is the critical zone?
includes the land surface and its canopy of vegetation, rivers, lakes, and shallow seas, and it extends through the pedosphere, unsaturated vadose zone, and saturated groundwater zone
Water balance equation (for a watershed/basin/hillslope)
P = Q + ET + S
P is precipitation
Q is runoff
ET is evapotranspiration
S is storage
Hillslopes
where streams are generated; fundamental/smallest unit of a headwater watershed
Vadose zone
shallow and unsaturated part of the subsurface
boundary between the top of the vadose zone and atmosphere boundary between bottom of vadose zone and water table
capillary fringe in the vadose zone just above the water table
Fates of precipitation with respect to a canopy
interception by tree canopy (storage, evaporation); stemflow down canopy into ground
Fates of precipitation with respect to the soil
infiltration into soil (storage, evaporation, flow)
Soil
mixture of solids (minerals) and voids (pores - liquids, gases, organic matter)
texture is defined by size of particles (clay, silt, very fine sand, fine sand, medium sand, coarse sand, very coarse sand) or texture class (clay, sand, silt)
texture determines how much water infiltrates into the vadose zone (capillary fringe) from saturated zone
organized by layers called horizons (porosity is highest at the surface (plants dig their roots, critters burrow); porosity decreases from surface to depth; porosity is effectively zero at bedrock; horizons affect if/how water enters then flows through vadose zone
Types of flow
surface (overland) - infiltration excess (more rainwater hitting surface of soil than can infiltrate into soil; excess rainwater flows horizontally and downslope across surface of soil; occurs often in urban settings and bare soil cover), saturation excess (rainwater hitting surface of soil can infiltrate down into soil; rainwater fills pores of soil, saturating the soil; occurs often in vegetated settings)
subsurface - matrix (largest contributor to flow in terms of volume). macropores (route water quickly through soil matrix; bypasses soil, so water does not interact biogeochemically with soil and organic matter; small component of overall flow in terms of volume; combine to form preferential flow paths)
flow is partitioned between surface and sub-surface compartments depending on infiltration rates of soil
Variable Source Area Concept
stream water comes from a source, the source is the landscape, source is defined area-ly not vertically, source area is typically near the stream during normal (dry) conditions, source area expands beyond near-stream environment and up to hillslope during storm (wet) conditions, source area is variable depending on storm conditions, source area gives information (type of soil water must move through, biogeochemical composition of stream water)
Fill and spill hypothesis
process explanation for threshold behavior in subsurface stormflow; Variable Source Area theory applied to different depths of soil profile (soil surface, bedrock [ridge, depression]), VSA theory combined with threshold response
transient subsurface saturation (shallow soil areas [upslope], bedrock depressions [midslope]), subsurface saturation expands downslope from the mid and upper hillslope (no saturated wedge expanding upslope)
bedrock microtopography is important (must be filled before water can spill downslope and connect to hillslope, when connectivity is achieved water moves > 5x faster); bedrock is not impermeable (water flows through cracks and fractures in bedrock, delays time to fill and spill)
lateral flow is restricted to bedrock depressions; bedrock depressions are spatially variable; subsurface stormflow is spatially variable; subsurface stormflow is not temporally variable (significant flow initiated after precipitation threshold is reached)
Stream sources
melted snow; swamps and puddles collect water on flat land which drains into stream; some water infiltrates and becomes groundwater; sheetwash flows over land into stream; rain or snow falls directly into stream; some water entering stream flows through soil first; groundwater enters stream via springs
Drainage networks of channels
dendritic
radial
rectangular
trellis
parallel
Types of streams
perennial (permanent); ephemeral (temporary and regular)
Stream discharge equation
width x depth x velocity
Base level
lowest point to which a stream can erode; adjustments can cause stream readjustments (raising base level increases deposition, lowering base level decreases deposition)
rise in base level causes filling with alluvium, fall causes downcutting of alluvium
Valleys
rivers downcut through soft sediment
Canyons
rivers downcut through hard rock
Braided streams
form where flow is forced around sediment obstructions
Alluvial fans
develop at base of a mountain when sediments drop out
course then fine material is deposited
Streams meander…
along lower gradient portion of the longitudinal profile
evolve over time
meandering cutoffs occur when cut banks converge and a meander neck thins (forms oxbow lakes)
Stream banks
stream cut bank (high-velocity) and deposit sediment at point bar (low-velocity)
cut banks erode while point bar accretes
Deltas
sediment deposits at mouth of a stream
deltas starved of sediment slowly compact, dewater, subside, and submerge
Avulsion
main channel may move to new location to establish steeper, shorter path
Evolution of drainage
beveling topography
stream piracy
drainage reversals
stream rejuvenation
superposed streams
antecedent and diverted streams
Floodwaters
high discharge and velocity spill out of stream channel
devastating to people (scours floodplains, alters landscape, destroys structure)
water input exceeds soil infiltration capacity (soil pores are saturated) - abrupt, heavy rains dump large volumes of water quickly; large, continuous rains dump large volumes of water slowly; abrupt, warm weather rapidly melts winter snow; a dam (natural or artificial) breaks, releasing water
Flood occurrences
seasonally (evacuation possible) - ex. monsoons, rainstorms
suddenly (evacuation impossible) - ex. rainstorms, dam and levee breaks
Flood recurrence intervals
flood risks are calculated as probabilities
Living with floods
sandbags and grading increase elevation of people and property
levees allow more channel volume
channelization controls course of flow
dams hold back water
Groundwater
water that percolates through vadose zone to reside in deep sediment or rock
flows slowly underground
resurfaces after months to thousands of years to rejoin the hydrologic cycle
Meteoric water
recharges (infiltration) the ground, then discharges (shallow subsurface and groundwater flow)
Porosity
primary porosity - open space within rock that originally formed with the material (ex. voids in sediment; vesicles in basalt; open cavities in reef limestone); decreases with burial compaction and cementation; crystalline rocks have little primary porosity
secondary porosity - new pore space created after the rock was first formed (ex. fractures, fault breccia, solution cavities)
different porosities of media - vesicular basalt (20%), limestone (25%), shale (5%), well-sorted sandstone (30%), poorly sorted sandstone (15%), granite (< 1%)
Aquitards
impermeable layers within aquifer
sediments or rocks that have low permeability located above sediments or rocks that have both high porosity and high permeability
Perched water table
groundwater that is trapped
Factors that affect water table depth
varies with climate and seasons
varies with precipitation
depth is a subdued replica of surface topography
Hydraulic head
potential energy due to elevation
weight of overlying water exerts pressure and drives flow
flow always moves from high to low hydraulic head
Calculation groundwater flow (Darcy’s Law)
Q = K(h1 - h2 / j)A
Q is discharge
K is hydraulic conductivity
(h1 - h2 / j) is hydraulic gradient
A is cross-sectional area perpendicular to flow
high permeability increases flow rate, low permeability decreases flow rate
steep gradients increases flow rate, gentle gradient decreases flow rate
hydraulic gradient indicated by slope of water table
flow rate is governed by permeability by media x hydraulic gradient
Installing wells to tap groundwater supplies for human use
causes cone of depression in water table after pumping and lowered water table
Artesian wells
tap confined aquifers
well that penetrates confined aquifers in which pressure causes water to rise up on its own to a level above the top surface of the aquifer
aquifers are pressurized by upland recharge
water rises to potentiometric surface (analogue of water table for a confined aquifer; above ground)
city water systems are designed like artesian aquifers (water tower establishes the potentiometric surface)
Springs
develop where water table intersects the surface
locations of natural groundwater discharge
important water resources for humans
Structural springs
flowing groundwater reaches a steep impermeable barrier (pressure pushes groundwater up to surface)
perched water table intersects surface (seep develops)
Hot springs
deep groundwater discharges along faults in geothermal regions
deep groundwater is warm
source of heat is geothermal gradient (shallow magma; circulation through faults)
Geysers
groundwater is heated by shallow magma
overlying water weight prevents boiling
bubbles form at surface so pressure drops
water below is superheated, transforms to vapor, boils at once, and is ejected
chamber is refilled with cooler groundwater
cycle repeats
Groundwater problems - overabundance
rise in water table
initiate slope failures
Groundwater problems - depletion
excessive extraction of groundwater
decline in water table
water table no longer intersects stream channel
streams and swamps dry up
Groundwater problems - reverse in flow direction
before pumping, septic effluent is carried by the regional
groundwater flow away from the home well
large irrigation well creates a large cone of depression
reverse in hydraulic gradient
Groundwater problems - saline intrusion at coast
freshwater less dense
saltwater more dense
freshwater “floats” on saltwater
pumping raises fresh/saltwater boundary
well is contaminated
groundwater becomes unpotable
Groundwater problems - subsidence
water in pore space acts to hold grains apart
groundwater is removed (sediments compress; pores collapse)
land surface cracks
land subsides irreversibly
can be slowed by engineering zones of inducted recharge
Groundwater problems - natural contaminants
unwanted substances (hardness, iron, arsenic, etc.)
removed by treatment
Groundwater problems - human caused contaminants
mine spoil and processing waters; petroleum terminals; abandoned gas stations; industrial solvents and degreasers; paints and thinners; junkyards; landfills; animal feedlot runoff; fertilizers; pesticides
groundwater transports pollutants away from source
creates contaminant plume (high concentration near pollutant)
can be cleaned up, but is expensive
Coastal tides
tilt of Earth’s axis; position of moon in its orbit; changing gravitational interplay; geometry of basin; barometric pressure
larger sublunar tidal bulge always faces the moon
Tidal reach
vertical difference between high/low tide
hypotenuse
Waves
build in response to wind blowing over surface of water
friction slows wave base; waves changes from circular to elliptical
oblique wave attack creates longshore current that moves sand along shoreland in zigzag path
wave refraction focuses wave energy on headland, accelerating erosion; deposition at embayments
when wave attack is head-on, water returns in rip current perpendicular to shore
Sediment budget
determines character of coastline
input: rivers, erosion of cliffs, wind
movement: longshore drift
output: blown off beach, sinking into deeper water, carried away by longshore currents
winter: stormy water mobilizes sand, sand is moved to offshore shelves, beaches are narrow and gravelly
summer: more moderate wave energy brings back sand, beach is replenished, beach is broad and sandy
Wave-cut notch
wave attack shatters and abrades cliff
Wave-cut bench
wave-cut notches progress until cliff collapses, process resumes, cliff retreats over time
Estuary
river valley flooded by sea-level rise 10-12 kya
Fjord
glacial valley flooded by sea
Organic coasts
coastal wetlands: trees, grasses, mosses, mangroves
coastal reefs: create large rocky structures of cemented skeletons; highly productive
Atoll
ring-shaped coral reef surrounding a lagoon and formed by eroding/sinking volcano
Coastal variability
glaciation/deglaciation traps or releases water, changing sea level
emergent coasts formed by erosion and uplift
submergent coasts formed by sea level rise and flooding
Coastal problems
sea-level rise could flood coastal cities
storms (like hurricanes) alter coastlines
Oceans
Pacific, Atlantic, Arctic, Southern, Indian
cover 70.8% of the planet
Continental lithosphere
floats high on mantle, and oceanic lithosphere floats deeper on mantle
Bathymetry
measurement of depth of water
passive margins, active margins, abyssal plains
Intertropical Convergence Zone
Sun hits most directly near equator (ITCZ)
warm, moist air rises to make clouds
clouds cool high in atmosphere and release precipitation
air comes back down at around +/- 30 degrees latitude
season migration of ITCZ is called Monsoon
responsible for much of global surface weather patterns
Water moves differently in subsurface
thermohaline circulation (heat + salt)
temp and salinity control density
density controls water movement: less dense water rises, moving to the surface; more dense water sinks, moving to bottom; when some water moves, then other water also moves to take its place
Temperature changes in water
change with depth more rapidly than salinity changes with depth
Salinity changes in water
changes with depth
governed by latitude-related evaporation vs freshwater input
Climate
average weather over a period of time in a specific place
Climate change
greenhouse effect traps heat (water vapor, greenhouse gases)
greenhouse gas emissions have increase significantly due to humans
CO2 responsible for biggest proportion of temp increase
increases heat content and evaporation
Atmosphere
air pressure decreases exponentially leaving earth
variations in air density and pressure cause air motion (wind)
air rises then cools adiabatically, forming tiny water droplets that make up clouds
temperature increases and decreases with distance from earth
atmospheric color depends on thickness of atmosphere that light passes through
Aurorae
charged particles from solar flares are funneled to poles by Earth’s magnetic field then interact with ionosphere
Winds
lateral pressure differences drive horizontal winds
air flows from high P to low P perpendicular to isobars
high-altitude winds are stronger at steps in the tropopause
winds are deflected by Coriolis effect
jet streams form at wavy boundaries where troposphere temps change dramatically
Seasons
due to 23.5 degree tilt of Earth’s rotational axis
Air mass
package of air with unique, recognizable properties that reflect its place of origin
flows over a region for days, changing local weather
Fronts
boundaries between air masses
curved surface that move with the air masses they separate
wave cyclones are common across mid-US
Cold front
occurs where cold air mass moves as a density underflow beneath warmer air
Warm front
develops when warm air pushes cold air as a wedge
move more slowly than cold fronts
have less steep temp and pressure gradients (warm air rising up front produces broad cloud cover)
Occluded front
combination front that develops when fast-moving cold front overtakes slower warm front
cold front lifts warm front off the ground, which generates “combination weather”
(Anti-)cyclone
air departing high pressure pulls down cold, dry air from above
air compresses and warms, yielding clear, dry weather
air spirals downward and clockwise at high-pressure air mass
air converges on low pressure and piles up, causing sir to flop up and out
rising air cools, condensing moisture, which builds rain clouds
cold front catches up to warm front (both fronts are connected at a V [center of low pressure])
resulting occluded front eventually dies out
Cyclone
air spirals upward and counterclockwise at low-pressure air mass
Clouds
form when water vapor in saturated air condenses as microscopic droplets of water or ice
rain forms when tiny droplets are large enough to fall due to gravity
type of cloud that forms depends on stability of air, temp at which moisture condenses, and wind speed
Convective lifting
occurs where warm air starts to rise
Frontal lifting
occurs where cold air pushes up warm air
Convergence lifting
occurs where winds merge and air has nowhere to go but up
Orographic lifting
occurs where moist winds run into mountain range and are forced to go up over it
creates rain-shadow deserts
Bacteria dominate cryosphere
harsh conditions
short trophic chains
bacteria responsible for biogeochemistry
bacteria are diverse in hillslope soils
Glaciations
moving ice formed by accumulation and compaction of snow
Glacier formation conditions
cold climate (polar latitudes, high elevation)
snow must accumulate (more snowfall than snowmelt, snow must not be removed by avalanches or wind)
Continental glacier
ice sheet that covers a continent
Dry-based (cold-based) glaciers
have their basal part entirely below the pressure melting point
move by internal deformation
Wet-based (warm-base) glaciers
have basal part at pressure melting point
melting water is lubrication for sliding
increased pressure of overlying ice increases pressure melting point (water exists in lower temps where it would have been frozen)
meltwater underneath the glacier (lubricates contact of ice to bed, reduces friction, allows for greater movement)
Glacier movement
move by sliding along crystal boundaries
composition of ice crystals affect movement of glaciers to form crevasses
move downslope by gravity
move outward rapidly and laterally
Distinct features of glacial-eroded landscapes
trunk valley, tributary valley, V-shaped valley, U-shaped valley, cirque, arete, horn, hanging valley, truncated spur, tarn
Sea ice
covers most of Arctic Ocean
fringes entire continent of Antarctica
Discharge
volume of water passing a reference point in a given time
Headward erosion
as time passes, water may dig into land at head of the channel, lengthening the stream by this process
Capillary fringe
where water seeps upward (due to surface tension) from saturated zones just above the water table
Stream piracy
natural process that happens when headward erosion by one stream causes the stream to intersect the course of another stream, “capturing” the water of the stream that it has intersected so that the water of the captured stream starts to flow down the
channel of the new stream
Thunder
crackling or rumbling noise that accompanies lightning because the immense energy of a
flash heats the surrounding air to a temperature of 8,000 deg to 33,000 deg C, causing it to expand and then collapse almost instantly
Pleistocene Ice Age
most recent ice age, whose impact on the landscape can still be seen today
Arete
residual knife-edged ridge of rock separating two adjacent cirques
Longshore drift
where waves reach the near shore at an angle, the active sand moves in a sawtooth pattern that results in the gradual net transport of sediment parallel to the beach
bioturbation
Stirring by living organisms
Exosphere
layer of air between 700 and 10,000 km, which is a gradual transition between the atmosphere and beyond; at 10,000 km, the gas concentration becomes the same as interplanetary space
gyre
Oceanic-scale currents that take water on journeys extending for thousands of kilometers
and have long-established names
Equilibrium line
boundary between the zone of accumulation and the zone of ablation in a glacier
Rogue wave
wave that rises two to five times higher than other large waves passing a location during a period of time
Gyre
oceanic-scale currents that take water on journeys extending for thousands of kilometers and have long-established names
Crevasse
open crack that develops by brittle deformation of a glacier
Relative humidity
ration between measured water vapor content and the maximum possible amount of water vapor that the air could hold (expressed as a percentage)
Coriolis effect
consequence of Earth’s rotation, which causes moving water to veer to the right in the northern hemisphere and to the left in the southern hemisphere
Pangea
The super continent that was present 200 Ma, before tectionic plates moved the landmass apart to what it is today. Dinosaurs walked Pangea.
Tidal range
vertical difference between sea level at high tide and sea level at low tide
Iceberg
large block of ice floating in the water
Carbon cycles
carbon transfers among near-surface reservoirs (ocean, atmosphere, and environment)
carbon is removed for long periods of time (limestones, shale, fossil fuels, methane hydrates)
carbon is removed for a short period of time (trees, animals)
carbon is returned to atmosphere (burning organic matter, metamorphism of carbonate rocks, degassing from the oceans, biotic respiration)
Greenhouse effect
some gases in the atmosphere absorb thermal energy and re-radiate it, warming the lower atmosphere
H2O is most important greenhouse gas
CO2 is second most important
How was the core of the earth formed?
when the earth was forming and was really hot, iron sank to the center ‘cause gravity.
Growth rings
thicker rings wetter and warmer conditions
thinner rings indicate drier and colder conditions
Plate tectonics
modify positions of continents, thus impacting ocean circulation
Protoplanet
A large body of matter in orbit around a star, thought to be developing into a planet
Global cooling
formation of coal and removal of large amounts of organic carbon during Paleozoic era coincided with global cooling
appearances of lichens and grasses decreased atmospheric CO2, leading to cooling
climate warmed for agriculture when Vikings settled in Greenland
Holocene
the past 15,000 years
What is the leading theory of how the moon formed?
A mars-sized protoplanet collided with earth, and the earth debris that broke away began orbiting the earth and formed the mass we now know as the moon.
Sunspots
magnetic storms that slow convection at Sun’s surface
Sun radiates less heat
Ga
giga anum, billions of years.
what are the types of tectonic plate interactions?
convergence, divergence, collision, and rifting.
Sea level is geologically unstable; __________preserve evidence of sea level changes
sedimentary
rocks
