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Mahopac Central School
District Curriculum 2003-04
Earth History
A. The “Big Bang Theory” is the accepted model of the beginning of the universe
1. It says that the universe began with a great explosion over 13 billion years ago –
evidence for this view includes:
a. all objects that emit light exhibit a red shift in their light
1) this means that all stars are moving away from us and the universe is
expanding
b. microwave radiation from the explosion is still detectable, today
2. Some of the matter created in the Big Bang collected to form stars
a. stars are mostly hydrogen
b. the fusion of hydrogen nuclei into helium nuclei powers stars like the Sun
c. this fusion reaction also produces electromagnetic energy including visible
light
B. Solar Systems consist of a star or stars with smaller objects in orbit around them
1. Planets are large, basically round objects that orbit stars in predictable paths
2. In our solar system there is one star (the Sun) and nine planets
3. Mercury, Venus, Earth, and Mars make up the small, rocky inner planets
a. Mercury is closest to the Sun, but Venus is the hottest planet
b. Venus has a carbon dioxide atmosphere which causes a massive
greenhouse effect
4. Jupiter, Saturn, Uranus, and Neptune make up the large, gaseous outer planets
a. Pluto, while an outer planet, is small and rocky like an inner planet
b. It has a very eccentric (oval) orbit for a planet
C. Some of the planets are orbited by natural satellites (commonly called moons)
1. Mercury and Venus have no satellites
2. Earth has 1, Mars has 2, Jupiter has over 60, Saturn, Uranus, Neptune have over
a dozen each, and Pluto has 1
D. Other objects, not big enough to be called planets, also orbit the Sun
1. Asteroids – the majority are found between Mars and Jupiter
a. most are smaller than the moons that orbit the planets
b. asteroids may have collided with the Earth in the past
2. Comets – mixtures of frozen gases, liquids, and rock. sand, and gravel size
solids – a “dirty snowball”
a. comets have very eccentric/elliptical orbits
1. some actually leave our solar system and return many years or even
centuries later
b. comets have a “head” and a “tail”
1. the head is the dirty snowball part
2. the tail is the gases and solids ejected from the head as it orbits the Sun –
the surface of the head boils away over time
3. the tail always points away from the Sun due to the solar wind – charged
particles ejected by the Sun
c. a comet may have collided with the Earth as recently as 1908
3. Some of the smallest bits of matter are known as meteors
a. a lot of meteors are debris left behind by the passage of a comet
b. there are times during the year when the Earth passes through meteor
swarms and we experience meteor showers
Mahopac Central School
District Curriculum 2003-04
E.
F.
G.
H.
c. most meteors are so small that they burn up in the atmosphere – they are
called “shooting stars”
d. the bigger ones can survive their fiery trip through the atmosphere and strike
the surface
1. these are called meteorites
e. large meteors are responsible for the cratered surface of some planets and
moons
Today, we know that the Sun is one of millions of stars that reside off one arm of the
Milky Way Galaxy
1. A galaxy is a collection of billions of stars and their solar systems
2. Our star, the Sun, is average in size, temperature, and age – if hollowed out the
Sun could hold one million Earths inside
3. The Milky Way Galaxy is one of billions of galaxies in our Universe
a. all galaxies are moving relative to one another
Early man believed in a Geocentric Model
1. It said the Earth was the center of the Universe, did not move at all, and the
planets, moon, Sun and constellations all were orbiting the Earth
a. it was believed that the Sun orbited us daily
b. it could happen this way and it does explain most of what we see around us
c. it could not explain the fact that some planets appear to move backwards
during part of the year
By the Middle Ages, another model – the Heliocentric Model – replaced the older
version
1. This model placed the Sun at the center of our Solar System with planets, their
moons, asteroids, comets, etc. moving around the Sun
a. it did explain why some planets appear to move backwards during the year
b. it assumed that the Earth and other planets rotated (spun on an axis) while
revolving around the Sun
2. This model believed that stars (other than the Sun) were vast distances away
from our star
3. This model said one Earth rotation = one day, while one Earth revolution around
the Sun = one year
Evidence for rotation
1. Foucault Pendulum
a. a pendulum, once set in motion, should continue to swing in that same
direction (inertia)
b. however, after a period of time the Foucault Pendulum appeared to change
its direction of swing all by itself
c. Foucault concluded that the Earth’s surface turned underneath an
unchanging direction of swing
1) the observer is carried along with the moving surface
2. Satellite Images – they can actually record the rotational motion
3. Star Trails
a. a camera pointed at the North Star takes a time exposure photo of the night
sky
b. arc-shaped star trails are produced - 15 of arc for every one hour of
exposure
4. Rising and Setting of the Sun
a. either the Sun revolves around the Earth (Geocentric Model) or the Earth
rotates from west to east once every 24 hours
Mahopac Central School
District Curriculum 2003-04
b. solar day = the amount of time it takes the Sun to cross one meridian back to
crossing that same meridian – about 24 hours
5. Coriolis Effect – objects moving across the surface of the Earth appear to be
deflected from a straight path
a. this is seen in winds and ocean currents
b. in the Northern Hemisphere, the deflection is to the right due to a
counterclockwise rotation
c. in the Southern Hemisphere, the deflection is to the left due to a clockwise
rotation
I. Evidence for Revolution
1. Parallax – over the course of one year the position between a nearby star and a
distant star appears to change slightly
a. it’s actually the Earth (observer) changing its position slightly
2. Constellations
a. those visible to the naked eye change in a repeating pattern as the seasons
pass
b. either stars go around us (Geocentric Model) or we see different parts of
space at different times of the year
3. Sun’s Apparent Diameter – the size as seen by the observer
a. this size varies in a cyclic fashion
b. it is the largest in winter (Jan 3) and smallest in summer (July 4)
c. either the Sun expands and contracts in a cyclic fashion or the distance
between the Earth and Sun changes in a cyclic fashion
4. Changing Seasons – this is the strongest evidence for revolution
a. the Earth rotates on an axis that is tilted 231/2 from the vertical
b. this axis always remains parallel to its position the day before
c. this causes the altitude of the noontime Sun and the duration of insolation to
vary in a cyclic pattern
1) Summer Solstice – June 21
aa.) the Northern Hemisphere is most tilted towards the Sun
bb.) the Sun is highest in the sky at noon
cc.) the duration of insolation is at its maximum
2) Winter Solstice – December 21
aa.) the Northern Hemisphere is most tilted away from the Sun
bb.) the Sun is lowest in the sky at noon
cc.) the duration of insolation is at its minimum
3) Equinoxes – Vernal (spring) and Autumnal (fall) – March 23 and Sept. 21
aa.) the axis is tilted neither towards nor away from the Sun (it’s still
tilted, though)
bb.) the Sun is at an average altitude in the sky at noon
cc.) the duration of insolation is at an average value worldwide (12 hours
of daylight and 12 hours of darkness for all on Earth)
d. if the axis weren’t tilted your season would never change
e. orbital motion (revolution) occurs when there is a balance between inertia and
gravity
f. Kepler determined that the orbits of the planets were ellipses (oval shaped)
although the Earth’s orbit is nearly circular
J. The Moon and its Motion
1. The Moon shines because of reflected light from the Sun
Mahopac Central School
District Curriculum 2003-04
a. the Sun lights up the half of the Moon’s surface that faces it, only – the side of
the Moon not facing the Sun is not illuminated
2. Due to its lower mass, the Moon has only 1/6th the gravity of the Earth
3. The gravitational pull of the Moon and the Sun on the Earth causes the rhythmic
rise and fall of sea level at the shore (called tides)
a. the Sun’s effect is negligible due to its great distance from the Earth
b. there are 2 high tides and 2 low tides every 24 hours (roughly) – the tide
changes every 6 hours (roughly)
c. spring tides = high highs and low lows – the Sun, Moon, and Earth must be in
a straight line in space
d. neap tides = low highs and high lows – the Sun, Moon, and Earth must be
meeting at a right angle in space
4. The Moon’s period of revolution and its period of rotation are the same – 27.3
days
a. this causes the same side to the Moon to always face Earth
5. A Lunar Month is the amount of time it takes the Moon to revolve from one New
Phase to the next New Phase – 29.3 days
a. the “extra” two days are due to the time it takes the Moon to “catch up” to a
revolving Earth
K. Moon Phases – the amount of lighted Moon surface visible from the Earth
1. The changing angle between the Sun, Moon and Earth causes the amount of
lighted surface visible from Earth to change from night to night
2. There are 8 basic Moon Phases:
a. New Phase – Sun, Moon, Earth meet in a straight line in space – once a
month – NO lighted Moon’s surface is visible from Earth
b. Waxing/New Crescent – Sun, Earth, Moon meet at an acute angle in space –
more than 2 per month – less than half of the right side of the Moon’s surface
is seen as lit
c. Waxing/New Quarter – Sun, Earth, Moon meet at a right angle in space – one
per month – the right half of the Moon’s surface is lit
d. Waxing/New Gibbous – Sun, Earth, Moon meet at an obtuse angle in space –
more than 2 per month – more than half of the right side is lit
e. Full Phase – Sun, Earth, Moon meet in a straight line in space – one per
month – all of the Moon’s surface visible from Earth is lit
f. Waning/Old Gibbous – Sun, Earth, Moon meet at an obtuse angle in space –
more than 2 per month – more the half of the left side is lit
g. Waning/Old Quarter – Sun, Earth, Moon meet at a right angle in space – one
per month – the left half of the Moon’s surface is lit
h. Waning/Old Crescent – Sun, Earth, Moon meet at an acute angle in space –
more than 2 per month – less than half of the left side of the Moon’s surface
is lit
i. New Phase starts the cycle all over again
L. Eclipses – when the shadow of one object lands on the surface of another object
1. Solar Eclipse – when the shadow of the Moon falls on to the surface of the Earth
a. the Sun is blotted out
b. the Moon must come between the Sun and the Earth
c. you have to be at the right place at just the right time to witness a solar
eclipse
2. Lunar Eclipse – when the shadow of the Earth falls on to the surface of the Moon
a. the Moon’s surface is blotted out
Mahopac Central School
District Curriculum 2003-04
b. the Earth must come between the Sun and the Moon (Full Phase)
c. all people on Earth can see a Lunar eclipse on the night it occurs
M. The Earth is the Moon’s “partner” in space – their gravity has them locked together
1. The Earth is layered
2. The Lithosphere is the solid, rocky outer portion of the Earth that extends about
100 Km. Into its interior
a. it includes the crust and the upper mantle
3. The Crust is the uppermost region of the lithosphere
a. while the crust is solid, it’s very unstable
4. The Mantle is the layer under the crust made up of a plastic upper mantle and a
stiffer lower portion
a. a plastic is a substance that has the properties of a liquid and a solid at the
same time
b. there are huge convection cells that circulate in the upper mantle
5. The Outer Core is a liquid Nickel/Iron mixture
6. The Inner Core is a solid Nickel/Iron mixture
a. generally, the deeper within the Earth you get the higher the temperature and
the higher the pressure
7. This layering of the Earth’s interior occurred when the Earth first formed
a. high density materials sank to the center while lower density materials floated
to the surface
8. The Earth has other layers as well
a. the atmosphere is the shell of gases that surrounds the Earth
1) the atmosphere itself is layered
b. the hydrosphere is the thin layer of water that rests on the lithosphere
1) this includes oceans, lakes, rivers, streams, and ponds
2) some water is stored in small openings (pores) underground – this is
called ground water
3) some water is stored in the frozen form of ice caps, glaciers, and icebergs
c. the biosphere is the community of plants and animals on the Earth
N. Weathering is what occurs when the lithosphere interacts with the atmosphere,
hydrosphere, or biosphere
1. It causes rocks and minerals to break down into smaller sediments
2. There are 2 types of weathering: Physical and Chemical
3. Physical Weathering changes the size and shapes of rocks but not their
chemical compositions
a. frost action – liquid water seeps into cracks and other openings in rocks,
freezes, expands, and splits the rock into smaller pieces – potholes form this
way
b. thermal action – repeated heating and cooling causes expansion and
contraction – these stresses can cause rocks to split into smaller pieces – it
happens in deserts, especially
c. root pressure – the pressure exerted by the roots of plants/trees growing into
small fissures in rocks can split the rocks into smaller pieces – seen in
sidewalks, commonly
d. abrasion – wind and running water carry small particles which act like
sandpaper and grind up larger rocks into smaller ones – this is how stream
channels grow in size
4. Chemical Weathering – not only are rocks and minerals broken down into smaller
pieces, their chemical composition is changed
Mahopac Central School
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a. hydration – some minerals are soluble in water – they dissolve – water is
known as the “universal solvent” because so many materials dissolve into it
b. oxidation – elements in rocks and minerals combine with oxygen and break
down – iron and other metallic elements oxidize well
c. carbonation – carbon dioxide gas dissolves into water to form carbonic acid
1) this acid dissolves many minerals especially calcite – the mineral in
limestone and marble
2) ground water containing carbonic acid can cause caverns to form in
limestone and marble
d. acid precipitation – sulfuric and nitric acids falling to the surface break down
rocks and minerals by dissolving them
O. Erosion – the processes where sediments (created by weathering) are moved or
transported
1. Gravity is the main force that causes erosion
2. The agents of erosion include running water, wind, and glacial ice
3. Running water is the most important of the agents worldwide
a. runoff occurs when precipitation rates exceed infiltration rates
b. streams and rivers transport huge quantities of sediments to oceans or other
standing bodies of water
c. they also carve up the land by abrasion
d. ocean currents transport small particles as well as dissolved matter
e. ocean waves are an erosional agent responsible for many of the features of
shorelines
4. Wind can transport small sediments, only
a. usually wind is effective in dry environments where there is little vegetation
5. Glaciers are large bodies of moving ice
a. they form when snowfall rates exceed melting rates
b. glaciers move under the influence of gravity, by plastic flow, and by sliding
over a thin layer of liquid water at their base
c. glaciers transport sediments of all sizes
d. much of the landscape of New York and New England were shaped by
glaciers
1) the Finger Lakes and Lake George of the Adirondacks were formed by
glacial ice
e. U-shaped valleys and fine striations (scratches in bedrock) are left behind
when glaciers recede or retreat
6. It is possible to limit erosion of the land
a. Planting vegetation – their roots hold the soil in place and prevent its
transport
b. Contour Plowing – plowing at right angles to hillslopes slows down running
water
c. On Long Island erosion can be reduced by stopping the destruction of natural
sand dunes
P. Deposition – when agents of erosion release particles they can no longer carry
1. Sedimentation is the processes by which the particles are deposited
2. Sediments moved by running water are deposited in the water or near a
shoreline
a. deltas at river mouths are an example
b. sediments on the bottom of stream channels are another example
3. Streams and rivers slow as the land flattens
Mahopac Central School
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a. this causes the stream to meander (to curve or wind back and forth)
b. water on the outside of a meander moves faster and can carry sediments
(accomplishes erosion)
c. water on the inside of a meander moves slower and drops sediments
(accomplishes deposition)
4. Ocean waves and currents move sediments forming beaches
5. With glaciers, if melting occurs in the front of the glacier, sediments are sorted by
size by the running glacial meltwater (these are called outwash)
6. Behind the melting front, sediments are deposited in an unsorted fashion (these
are called till)
7. Wind forms sand dunes
a. these cut down on beach erosion
b. housing developments on Long Island have destroyed the dunes and
resulted in excessive beach erosion
8. Minerals dissolved in seawater are left behind when the water evaporates
a. halite (rock salt) and gypsum are deposits formed this way
Q. Soils – soils are formed from weathered rock
1. Some soils form from the weathering of local bedrock – others from sediments
deposited by agents of erosion
2. The length of time for formation of soils varies with the type of bedrock and the
climate of the area
3. Soils contain a number of layers
a. the soil in which food/crops are grown is called topsoil
b. it contains weathered sediments plus organic matter (decayed plants and
animals and the wastes of both)
4. Many organisms living in the soil fertilize it and aerate it
a. the waste products are the fertilizer
b. adding space for air to circulate is aerating it
c. bacteria that live in the roots of plants convert nitrogen from the air into
nitrates which act as fertilizer
d. these bacteria cycle nitrogen between the lithosphere and the atmosphere
R. Minerals
1. A mineral is a pure substance made up of only one type of matter
a. a pure substance can be an element or a compound
2. Minerals are identified on the basis of 5 properties
3. Hardness – the resistance of the mineral to being scratched
a. this is usually stated in terms of Moh’s Scale of Hardness and assigns the
mineral a number from 1 to 10
4. Streak – the color of the powdered mineral
5. Cleavage – the tendency of a mineral to break along regular surfaces in one or
more specific directions
6. Luster – how the mineral’s surface reflects light
7. Reaction to Acid – calcite is identified because it reacts with Hydrochloric Acid to
form bubbles of carbon dioxide gas
S. Rocks and the Rock Cycle
1. Rocks are any collection of 1 or more minerals
2. Rocks can be classified (divided into groups) on the basis of how they formed
3. There are 3 classes of rocks: Sedimentary, Igneous, and Metamorphic
4. Sedimentary Rocks – formed from the accumulation of sediments
Mahopac Central School
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a. some form when rock fragments (sediments) settle in water or are deposited
on land and the grains are cemented together
1) sandstone is a good example
b. some form by compaction – the weight of the overlying sediments causes
them to be pressed together
1) coal and shale are good examples
c. some form when ancient oceans evaporate away leaving behind the
dissolved salts
1) halite is a good example
d. sedimentary rocks show layering and only sedimentary rocks can contain
fossils
1) a fossil is any remains of past life
2) it may be the entire organism, an imprint, bones, shells or formed when
minerals replace living tissue (petrification), or an imprint can fill with
sediments forming a cast
3) fossils allow scientists to infer certain things about a regions climate and
environment at the time the living organism died
e. layered sedimentary rocks can tell the relative age of fossils
1) the oldest are on the bottom and the youngest are on the top of the
sequence of layers
5. Igneous Rocks – rocks that crystallize from molten (melted) materials
a. the molten rock may be underground (magma) or flowing on the surface or
flying through the air (lava)
b. igneous rocks that cool slowly from magma have large crystals – like granite
c. igneous rocks that cool quickly from lava have small crystals – like basalt
d. some lava cools so quickly that the crystals are invisible – forming natural
glass called obsidian
e. lava can mix with air to form a solid “froth” – this is called pumice
f. igneous rocks are classified by their mineral content and where they cooled
6. Metamorphic Rocks – a rock having undergone a change in form
a. heat and pressure are what usually cause a rock to change into a
metamorphic rock
b. these conditions are found within the Earth
c. under extreme heat and pressure minerals will migrate into zones
1) this gives some metamorphic rocks a color banded appearance
d. great heat and pressure cause the rocks density to increase, too
7. Rock Cycle – any type of rock can become another type of rock
a. cooling and solidification of molten materials yields an igneous rock type
b. weathering, erosion, and deposition produce, transport, and release
sediments
c. these sediments can form sedimentary rocks which pile up in layers
d. as heat and pressure grow on the bottom of the pile, metamorphic rocks can
form
e. if enough heat is generated rocks melt into magma and the cycle begins
again
f. there are “shortcuts” in the cycle that can occur, too
T. Plate Tectonics
1. Alfred Wegener proposed the Theory of Continental Drift after he noted that
certain continents appeared to fit together like pieces in a jigsaw puzzle
Mahopac Central School
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a. he also noted that plant and animal fossils found along the coastlines of
matching continents also matched up
2. Continental Drift says that all continents were once joined into one
“supercontinent” called Pangaea
a. Pangaea broke apart and over millions of years the pieces drifted into the
present position of our continents
b. convection currents in Earth’s interior are what powered the floating
continents along
3. The Theory of Continental Drift eventually gave rise to the modern day Theory of
Plate Tectonics
a. this theory states that the lithosphere is broken into a series of pieces called
plates
b. each continent is attached to its own plate – 6 huge pieces
c. there are numerous smaller pieces which carry no continent but still move
d. all these plates float and they move due to convection cells circulating in the
upper mantle
e. earthquakes and volcanoes occur at plate boundaries (where plates meet)
U. Plate Boundaries
1. When two continental plates collide, mountain building occurs
a. the Himalayas are the best example
2. When an oceanic plate (the thinner of the two) collides with a continental plate
(the thicker of the two), subduction occurs
a. the higher density, thin oceanic plate slides down under (subducts) the
thicker continental plate
b. ocean trenches are formed this way
c. volcanic mountain ranges form at subduction zones
1) the Cascade mountains of North America formed this way
d. island arc systems form – like the Japanese Islands or the Aleutians
3. Two oceanic plates can collide – this type of subduction produces trenches, too
4. Oceanic plates can pull apart – this causes mid-ocean ridges to form
a. molten rock from below flows out on to the ocean floor causing it to spread
and grow larger
b. the Mid-Atlantic Ridge is the best known example of this phenomenon
1) Africa and South America are moving apart as are North America and
Europe
2) Zones of subduction form at the opposite edges of the spreading oceanic
plates
3) South America and Africa must have been attached, split apart, and
oceanic crust filled the void between them
5. Continental crust can pull apart, too – this causes a Rift Valley to form
a. the Rift Valley of southeastern Africa is the best example
6. Ocean plates can drift over a “hot spot” – a rising plume of magma
a. rising magma melts through the plate, piles up, and a volcanic island is
formed
b. the plate moves on and a new, younger volcanic island is formed
c. the Hawaiian Island chain is the best example of this phenomenon
7. Plates can slide past one another – this is called a transform plate boundary
a. the San Andreas fault is a boundary between the Pacific plate and the North
American plate
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b. Los Angeles sits on the Pacific plate while San Francisco sits on the North
American plate – these cities are moving towards each other
V. Volcanoes – they form when magma reaches the surface through a crack in the crust
1. Most volcanoes occur in chains at plate boundaries
a. the “Ring of Fire” is a string of volcanoes that encircles the Pacific Ocean
b. zones of subduction and mid-ocean ridges produce chains of volcanoes
c. the flow of magma is gradual at mid-ocean ridges and more violent at zones
of subduction
2. Magma that reaches the surface is called lava
a. lava plateaus can form as layers of lava build up over the years
b. lava flowing from vents (roundish openings) create cone-shaped volcanic
mountains
3. Sulfur dioxide released from volcanic vents enters the atmosphere
a. it combines with water to form small sulfuric acid droplets
b. these droplets reflect sunlight and have a cooling effect on the lower
atmosphere
c. eventually, they fall to the ground as acid rain
W. Earthquakes – vibrations in the solid Earth
1. They are caused by faulting – rocks sliding past one another as a result of trying
to relieve stress
a. some faults are just plate boundaries like the San Andreas
2. The energy released by an earthquake travels through the Earth in the form of
seismic waves
a. primary waves have a longitudinal form and travel fast
b. secondary waves have a transverse form and travel slower
c. a seismograph is an instrument that detects and records the passage of
seismic waves through the Earth
3. The focus of an earthquake is the place where the fault moves
4. The epicenter of an earthquake is the place on the surface of the Earth directly
above the focus
5. If an earthquake happens in the ocean, a tsunami can occur
a. a tsunami is a giant ocean wave
b. it can travel at almost 600 mph – it passes unnoticed in deep ocean water
c. as they move from deeper to shallower water, they stand up – some as high
as a 10 story building
6. The strength of an earthquake is measured on two different scales
a. the Richter scale measures the actual amount of energy coming from the
earthquake
b. it uses a scale of 1 to 9
c. each value on the scale is a logarithm – a power of 10 – so each increase in
numerical value means 10 times more energy was released
d. the Mercalli scale assigns a number based on the damage the earthquake
causes
1) this is more subjective than the Richter scale
2) the damage varies with population density and building codes
7. Seismic Hazards & some solutions
a. buildings and bridges collapse – improved building codes call for steel
reinforcements to such structures
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b. roads and railroad tracks are displaced – all vehicles stop immediately the
moment the earthquake is detected – again, improved building codes
requiring stronger materials used in road and track construction
c. fires from ruptured gas lines – automatic shut off valves limit escaping gas at
the first breach in a line
d. landslides – don’t build structures at the base of steep slopes in earthquake
prone regions
e. falling debris – get far away from all buildings, especially glass wrapped
skyscrapers
f. tsunamis – get to high ground and away from shorelines immediately after
the earthquake
g. families become separated – have a family plan to meet at a particular time
and at a particular place after such a natural disaster strikes