Final Exam ESCI 1000

Final

Climate, Weather and the Atmosphere

• Currently, the climate is warming
• Based on decades of warming in atmosphere
• Also, global increase in sea temp, widespread melting of snow, glaciers, ice sheets, and permafrost, and sea level rise
• Earth’s climate includes interactions of: Atmosphere, Hydrosphere, Geosphere, Biosphere, Cryosphere.

Referred to as global warming

• 99% probability that humans are responsible
• Ecosystems capable of adjusting, but changes are too fast for these to take place

Definition of WEATHER and CLIMATE

• Weather – conditions of atmosphere at
particular time and place
• Climate – long-term average of weather

Earth’s temperature depends on
three things:

1. Amount of sunlight received
2. Amount of sunlight reflected
3. Degree to which the atmosphere
retains heat

Greenhouse effect is a natural and necessary process.

• Earth would be 33C colder without it
• All surface water would be frozen.
• Little life would exist.
• Natural effect is from water vapor.
• 66–85% of greenhouse effect
• Absorption by greenhouse gasses (carbon dioxide,
methane, nitrous oxide, CFCs and ozone)
• Enhance the greenhouse effect

1. Permanent Gases
2. Variable Gases

1.
•Concentrations of which do not change
• Ex: nitrogen, oxygen
• Nitrogen composes about 78% of the volume of all permanent
gases
• Relatively unimportant to atmospheric dynamics
2.
• Concentrations of which vary in time and space
• Ex: carbon dioxide, water vapor, methane.

Carbon Dioxide

Makes up a very small percentage of the atmosphere
• Released naturally by volcanic activity, plant and animal
respiration, wildfires, and decay of organic material
• Removed through photosynthesis, chemical weathering, and
absorption by sea water
• It also enters the atmosphere through the burning of fossil fuels by people
• Increased greatly since the Industrial Revolution
• Recent change unprecedented, more likely the result of human activity rather than natural causes

Methane (CH4)

• Primary constituent of natural gas
• Occurs naturally from bacterial decay, intestinal tracks of
termites, cows, and sheep
• Anthropogenic sources: coal mines, oil wells, leaking natural gas pipelines, rice cultivation, landfills, and livestock
• Levels have doubled since 1700 and is a significant contributor to warming

Ozone O3

• Forms when atomic oxygen (O) collides with oxygen molecule
(O2)
• Mostly found in stratosphere
• Acts as a shield for ultraviolet light and is essential to life on earth
• Chlorofluorocarbons (CFCs) partially destroyed ozone shield
• Increases skin cancer, cataracts, caused local crop failures

Aerosols

• Microscopic liquid or solid particle that acts as nuclei for
water particles to condense to form clouds
• Associated with air pollution
• Natural sources: desert dust, wildfires, sea spray, and
volcanoes
• Anthropogenic sources: burning of forests and fossil fuels
• Effects are complex

Paleoclimatology & Proxy Data (6)

Paleoclimatology
• Analyzing proxy data in order to reconstruct past climates
Proxy data – indirect evidence using natural recorders of climate variability
1. Tree Rings
2. Sea Floor Sediments
3. Ice Cores
4. Corals
5. Pollen
6. Historical Documents

1. Tree Rings

• Growth of trees depends on rainfall and temperature
• Dendroclimatology: climate data provided by tree rings
• Proxy record that extends back more than 10,000 years

2. Sea Floor Sediments

• Recovered by coring lakes and ocean basins
• Samples are analyzed to provide data on climate change

3. Ice Cores

• Obtained by drilling into the ice
• Contain small bubbles of air deposited at the time of snow
• Composition of past atmospheric gases are studied

4. Corals

• Their skeletons have alternating light and dark layers that result from seasonal changes in growth rates. The light and dark layers represent annual bands, similar to tree rings, that can be used to determine the age of the coral skeleton. Variations in the chemical
composition of the skeleton can be calibrated to environmental parameters such as seawater temperature, salinity, and pH as the coral grows.

5. Pollen

• Accumulates with sediment in a variety of environments
• The types of pollen found reflects climate
• Preserved in sediment layers that can be independently dated
• A chronology can be developed
• Composition of past atmospheric gases are studied

6. Historical Documents

Books, newspapers, personal journals, ship logs, crop records
• Measurements of temperature and precipitation date to the late 17th
century
• Carbon dioxide in the atmosphere has been measured since 1958

Climate Change on Short Term Scales: Solar Forcing

• Solar energy changes
1. Variable energy from the Sun over time
2. Luminosity
3. Sunspots
4. Faculae
• Lack of correlation between solar activity and average Earth
temperature.

Variations in Earth’s Orbit: Milankovitch Theories (3)

1. Orbit or Eccentricity
2. Tilt
3. Wobble/angle or precision

Variations in Earth’s Orbit

• Changes in Earth’s orbit around Sun, tilt and wobble of Earth’s axis of rotation.
• Orbit – 100,000yrs – orbit
• Tilt – 41,000 yrs – angle of Earth’s axis
• Wobble – 26,000 yrs wobble of axis
• Variations contribute to glacial and interglacial episodes

Volcanic Forcing

• Ash from eruptions becomes suspended in the atmosphere, reflects sunlight having a cooling effect.
• Mount Tambora, 1815 eruption contributed to cooling in North
America and Europe.
• Volcanic ejecta may block sunlight
• Need many eruptions in short time period
• Not observed in recent history

Human Forcing

Intergovernmental Panel on Climate Change (IPCC)
• Global group of scientists
• Peer-reviewed literature
• Published assessments since 1990

There is sufficient evidence to state:
1. There is widespread evidence of human influence on global climate.
2. Warming is now occurring.
3. Mean surface temperature of Earth will likely increase between 1.40 and 5.80 C during this century.

Hazards Associated with Climate Change:

• Sea surface temperatures risen mostly since 1970
• Deep waters showing increases

Hazards Associated with Climate Change:

• Circulation of ocean water in oceans
• Can cause fast changes in climate
• Keeps Northern Europe warmer than without it
• Cold dense water sinks - oxygen

Hazards Associated with Climate Change:

Increased Hurricane Activity
• Warmer water fuels hurricanes
• Severity of recent Atlantic hurricanes
• Number of global tropical storms have not increased worldwide
• Intensity of storms has increased
• More Category 4 and 5 hurricanes (Warmer Ocean= bigger hurricane aka intensity)

Climate Patterns

• Changes in Climate Patterns: Increased Storm's
• Temperature and precipitation patterns, soil moisture
• Increase in the frequency or intensity of violent storms
• Change in the frequency and strength of El Nino and La Nina events (they get stronger)

Hazards Associated with Climate Change:

• Rising Sea Level – already occurring
• Main contributors:
• Melting of Antarctic and Greenland ice sheets
• Thermal expansion of ocean surface waters
• Melting of land glaciers and ice caps
• Thermal expansion of deep-ocean waters

Hazards Associated with Climate Change:

• Polar Ice Melting
• Arctic amplification
• Loss of more than 2 million square kilometers (800,000 square
miles) of Arctic sea ice in last decade
• Loss of ice = enhanced warming due to lower albedo

Hazards Associated with Climate Change:

Polar Ice Melting
• Arctic ice melting affects polar bear survival.
• Food sources are dwindling for human Arctic dwellers.
• Marine species migration

Hazards Associated with Climate Change: Climate Patterns

Thawing of Permafrost
-Release of carbon dioxide into the atmosphere from the decay of organic sediments

Hazards Associated with Climate Change:

• Climate change models can mimic modern conditions only if
human emissions are taken into account.
• IPCC assessments continue to provide strong documentation of
human-induced climate change.
• The concentration of atmospheric carbon dioxide was
approximately 280 ppm in 1750
• Today, the concentration is 413ppm
• Expected to reach at least 460 ppm in 2050

Hazards Associated with Climate Change:

• Some atmospheric carbon dioxide dissolves in ocean water
– produces carbonic acid
• Acidifies ocean
• Unable to make calcium carbonate shells
• Threatens calcifying organisms such as Coccolithophores, Foraminifers, Sea urchins and corals

Threshold 480ppm

Hazards Associated with Climate Change:

Ocean Acidification.
(Anything that has a shell will dissolve)

Hazards Associated with Climate Change: Climate Patterns

Desertification
• Human-induced degradation of productive land
• Preceded and accompanied by loss of vegetation and soil erosion
• Land may lose productiveness and not recover for decades or centuries
Drought
• Could increase in length and severity
• Areas that become drier and warmer will have more droughts
• Drought in Canada could be exacerbated by a reduction in the amount of snow and glacier ice
• Will have an effect on summer streamflow in many areas

Hazards Associated with Climate Change: Climate Patterns

Wildfires:
An increase in wildfires in many regions
Accelerate replacement of ecosystems that are poorly adapted
to a warmer climate with ones that can tolerate more warmth

Minimizing the Effects of Global Warming: International Agreements

• Montreal Protocol
• 1987 agreement to limit depletion of the ozone layer by CFCs
• CFCs have declined since the protocol was implemented
• Kyoto Protocol
• 1997 agreement from the United Nations Framework Convention on climate change
• Establishes targets for nations to reduce greenhouse gas emissions by 2012
• Canada was a signatory but recently withdrew after emission targets were not being met
• Withdrawal of the U.S. has severely reduced its effectiveness

Minimizing the Effects of Global Warming: International Agreements

Summit in The Hague, 2000
• 2000 conference that focused on alternative methods to reduce
emissions including:
• Clean development methods that improve the carbon balance of
developing nations
• Joint implementation, which allows emission credits to be shared between developing countries and wealthy countries
• Emission trading, where countries that easily meet targets can sell credits to countries that fail to meet their own
• The conference ended without an agreement
Paris Climate Agreement, 2017
• The agreement sets out a global action plan to put the world on track to avoid dangerous climate change by limiting global warming to well below 2°C.
• The US withdraws from the accord – only country do to so

Minimizing the Effects of Global Warming: Carbon Sequestration

• A process that refers to the capture and storing of carbon
dioxide before it enters the atmosphere
Biological sequestration
• Planting more trees
Oceanic Sequestration
• Injecting carbon dioxide deep in the oceans
Geological Sequestration
• Power plants and industrial facilities designed to capture CO2
• CO2 is then compressed and injected under pressure into wells drilled into the crust

Minimizing the Effects of Global Warming

• Two scenarios for climate change and sea level rise during the next 100 years
• Both scenarios assume economic growth, with population peaking in the middle of the 21st century
• Scenario 1
• More efficient energy technologies, but still fossil fuel intensive
• Average temperature will rise by about 4.5°C and sea level may
rise by 1.4 m
• Scenario 2
• Clean resource-efficient technologies, economic systems change
• Average temperature will rise by about 2°C and sea level may
rise by 0.5 m

(We'll most likley be in scenario 1)

Introduction to Wildfires

• Nature’s oldest phenomena.
• Before humans, fires would burn until they ran out of fuel naturally.
• Initiates plant re-growth, when the cycle restarts.
• Natural fires allowed humans to harness fires for their uses.
• Heat, light, cooking, hunting, etc.
-Lightning is the #1 product to start wildfires 2/3.
-Also, human caused-campfire & smoking 1/3.

Introduction to Wildfires (map) *Boreal Forest

• During a typical year there are over 9,000 forest fires in Canada, burning an average of 2.5 million hectares (ha) or 25,000 square kilometers. The number of fires and area burned can vary dramatically from year to year.

Wildfire as a Process
(Definition & 3 phases)

• Essentially, wildfires are a way to remove vegetation
• Fires reverse the process of photosynthesis
• Carbon dioxide, water vapor, and heat released
• Water vapor and carbon dioxide are the most abundant gases
released in fire
• Others (e.g., nitrogen oxides, carbon monoxide, and methane) are
released in trace amounts
• These gases along with ash and soot comprise part of the smoke
• Three phases of a wildfire
1. Pre-ignition
2. Combustion
3. Extinction

1. Pre-ignition

1.
• Fuel achieves temperature and humidity favorable to ignition.
• Preheating
• Fuel loses water and other chemical compounds
• Pyrolysis
• Processes that chemically degrade fuel
• Products include volatile gases, mineral ash, tars, etc.
• Heat, radiating from flames, causes both preheating and pyrolysis in advance of the fire
• These processes produce the fuel gases

2. Combustion

2.
• Begins with ignition
• Preignition absorbs energy, combustion releases energy
• External reactions liberate heat and light
• Ignition doesn’t always lead to wildfires - Sufficient fuel must
be present
• Ignitions are common on time scale relevant for mature vegetation
• In period of 50 to 100 years, every acre of land is struck by
lightening

2. Combustion

2.
• Flaming combustion
• Dominates early fire
• Rapid high temperature conversion of fuel into heat
• Characterized by flames and large amount of unburned
material
• Smoldering combustion= releases ash
• Takes place at lower temperatures
• Does not require pyrolysis for growth
Fuel, Weather and Topography
Fuel- Time, size, arrangement (crowded or not), types (canopy)
Weather- Hot, low humidity, wind
Topography- Slopes

3. Extinction

3.
• Point at which combustion, including smoldering, ceases
• There is no longer heat and fuel to sustain fire
** Every type of fire always has all 3 steps.

Types of Fires

• Classified according to the layer of fuel that is allowing the fire to
spread

1. Ground Fires

1.
• Creep along underground surface
• Little flaming, more smoldering
• Burn through the litter and humus layers
• Fires occur during periods of drought

2. Surface Fires

2.
• Move along surface
• Vary in intensity
• Burn slowly with smoldering, limited flaming
• Burn the upper litter layer and small branches on ground
• Do not consume all organic matter

3. Crown Fires

3.
• Occur when surface or ground fires ignite lower branches of standing trees
• Flaming is carried via tree canopies.
• Driven by strong winds and steep slopes.
• Generate tremendous heat – convection column, drawing in
surface winds

Effects of Wildfires (6)

• Affect many aspects of the local environment
1. Burn vegetation
2. Release smoke into the environment
3. Char soil
4. Create favorable conditions for landslides
5. Increase erosion and runoff
6. Harm wildlife
• Important to consider changes that may occur in the geologic and atmospheric environments

Effects of Wildfires

• Wildfires create their own clouds
• Release smoke, soot, and gases contributing to air pollution
• Significantly increase concentration of particulates
• Can be observed thousands of miles downwind
• Contribute to smog formation
• Release large quantities of carbon monoxide, volatile organic
compounds, and nitrogen oxides
• Form harmful ground-level ozone

Effects of Wildfires

• Effects can vary from moderate to severe, depending on the fire
type, size, location, duration, and intensity
• Can affect:
Vegetation
• Some plants are susceptible to fire, whereas others are not
• Can make plant vulnerable to later destruction by disease or drought
• Some plants use fire to propagate
• Important long-term control of plants
Animals
• Most animals may flee or hide unharmed
• Habitats are altered
• Can determine the type and number of vertebrates that can thrive

Effects of Wildfires

Humans
• Water quality is affected through increase of erosion potential
• Smoke and haze produce eye, respiratory, and skin problems
• Destroys personal property
• More and more living on the fringes of wildlands in the wildland-urban interface
• Naturally occurring fires surpressed resulting in longer return intervals and accumulation of fuel

Effects of Wildfires

• Climate change increases intensity and frequency of wildfires.
• Caused by changes in temperature, precipitation, and the frequency and intensity of severe storms.
• Increases in temperature, decreases in humidity.
• Grasslands replacing forests creating more fuel.
• Lightning strikes increase ignitions.
• Insect infestations make trees more vulnerable to fire.

Minimizing the Wildfire Hazard: Fire Management

• Task is decided when fires should be allowed and when suppressed
• Science
• Fire regime for site
• Types of fuel available
• Fire behavior
• Fire history
• Education
• Educating people to reduce their risk

Minimizing the Wildfire Hazard: Fire Management

• Data collection
• Mapping vegetation and potential fuel
• Moisture content
• FPI (Fire Potential Index) maps
• Prescribed burns
• Controlled burns to manage forests
• Reduces fuel for more catastrophic fires
• Necessary to predict the behavior of the fire and control it

Benefits From Wildfires

•Benefits to soil:
-increasing nutrient content
•Benefits to plants and animals:
-reduce bad microorganisms )
- reduce number of species of plants) No competition
-can release seeds
-more sunshine will produce more plants (no canopy)
-release nutrient back onto soil

Introduction to Coastal Hazards

• Coast also influenced by geology, climate and organisms.
• Canada has longest coast in the world.
Coastal hazards include:
• Strong coastal currents
• Coastal erosion
• Sea-level rise
• Storm surge
• Tsunamis

Introduction to Coastal Hazards: The Shoreline

pic

Introduction: Waves, Currents and Coastlines

Waves are generally produced by the wind, but there is other
mechanisms:
Splash Wave
• coastal landslides, calving icebergs
Seismic Sea Wave or tsunami
• sea floor movement
Tides
• gravitational attraction among Moon, Sun and Earth
Wake
• ships

Wave Generation: Wave Size (3)

• The size of waves in deep water depends upon:
1.Wind Speed
2.Wind duration
(how long does it blow in the same direction?)
3. Fetch
(the distance of open water over which the wind blows)

Wave Generation: Maximum Wave Height

• Wave height is directly related to the energy of the wave
• Waves heights in the sea – less than 2m, but can reach to 10m
• U.S. Navy Hydrographic Office – maximum wind generated waves to be no higher than 18.3m (60 ft).
• Waves become sorted into groups.
• Rogue waves are exceptions to these groups
• In fact, several large ships disappear every year

Wave Generation: Maximum Wave Height

• USS Ramapo (1933): 152-meters (500 feet) long ship
caught in Pacific typhoon
• Waves 34 meters (112 feet) high

Wave Dynamics: Wave Definitions

• Wave height (H)
• Distance from crest to trough
• Wavelength (L)
• Distance from crest to crest
• Wave period
• Time between crests
• C = wave velocity

Wave Dynamics: Wave Characteristics

• Diameter of orbital motion decreases with depth of water.
• Waves in shallow water become ellipses as waves “feel bottom.”
• When depth is 1/2 wavelength
• Hardly any motion below waves base due to wave activity

Wave Dynamics: Waves Approaching Shore

As a deep-water wave becomes a shallow-water wave:
1. Wave speed decreases
2. Wavelength decreases
3. Wave height increases
4. Wave steepness (height/ wavelength) increases
5. When steepness 1/7, wave breaks

Wave Dynamics: Sand Transport

Two Major Types:
1.Perpendicular to shoreline (toward and away)
• Swash – water rushes up the beach
• Backwash – water drains back to the ocean
2. Parallel to shoreline (up-coast or down-coast)
• Longshore drift – transports sand along the beach.
Sediment is moved in zig-zag steps along the shore.

Wave Dynamics: Tides

Regular variations in sea level as a result of: The Moon (2/3 rds) and the Sun (1/3 rd)
Spring tides:
• New or full moons
• Tidal range greatest
Neap Tides:
• Quarter moons
• Tidal range least

Wave Dynamics: Tidal Ranges in Eastern Canada

• Burntcoat Head
• Highest Tides in the World
• >16m
Why so high?
a. shape of channel- width depth
b. resonance of tides
c. moon and sun interactions

Wave Dynamics: Tidal Ranges in Eastern Canada

pic

Coastal Hazards – Rip Currents

• Currents that move away from shore.
• Develop when waves pile up water between longshore bar and swash zone.
• Becomes concentrated in narrow zones
•In U.S. 100 people are killed by rip currents.
• Currents are narrow and widen and dissipate once they reach line of breaking waves
• Escape requires swimming parallel to shore
• Don’t panic!

Minimizing Coastal Erosion – Cliff Erosion

• Sea cliffs and lakeshore bluffs erode due to wave action, running water, and landslides
• Causes the cliffs and bluffs to retreat
• Human activities increase erosion rate
•Increase surface runoff
•Increase groundwater discharge
• Addition of weight to cliff
• Can be monitored using LIDAR.

Minimizing Coastal Erosion (4)

• Hard stabilization
• Creating structures meant to protect shoreline
1. Groins
2. Sea Walls
3. Jetties
4. Break Waters
• Soft stabilization
• Adding sand to depleted beaches
• Land use changes
• avoid building in hazardous areas

1. Groins

1.
• Structures built perpendicular to shoreline usually in groups
• Traps sand from longshore drift
• Causes increased erosion in down-drift area

2. Sea Walls

2.
• Structures built perpendicular to shoreline usually in groups
• Traps sand from longshore drift
• Causes increased erosion in down-drift area

3. Jetties

3.
• Built perpendicular to shore
• Built in pairs
• Built to protect harbor entrances

4. Break Waters

4.
• Built parallel to a shoreline
• Designed to protect harbors from waves
• Can cause excessive erosion, requiring dredging to keep area
stable

Minimizing Coastal Erosion – Soft Stabilization.

Beach Nourishment
• Adding sand to replace sand that has eroded.
• Aesthetically preferable to hard stabilizations.
• Temporary solution.
• Sand must be chosen carefully to match conditions at beach.

Artificial Bypassing

- Marina del Rey
- sand pumping system (pics)

Minimizing Coastal Erosion

Relocation
• Move structures rather than protect them in areas
of erosion
(pics)

Human Interaction with Coastal Processes

Atlantic Coast-characterized by barrier islands
Removal of coastal dunes
• Increased vulnerability to storms
Jetty construction
• Interrupts longshore drift
• Increases erosion at some locations
Point Pelee
-coastal erosion owning to sediment starving

Linkages with other Natural Hazards

Earthquakes, volcanic eruptions, tsunamis
• Change the shape of shoreline
Storm waves, storm surge, and coastal flooding
• Increase coastal erosion
Landslides
• Caused by eroding cliffs and bluffs
Climate change
• Storm frequency and intensity change with climate conditions

Natural Service Functions (3)

Pleasing Landscapes
• Cliffs and bluffs are result of erosion
Beaches
• Maintained or created by erosion and deposition
Recreation
• Swimming, sailing, fishing, and sunbathing

Perception of Coastal Hazards

•Perception of erosion hazard depends on people’s experience, proximity to the coastline, and probability to suffering damage
•Many people are complacent about wave and current hazards

Earth’s Place in Space

• The universe was created in an explosion known as the “Big Bang” 14 billion years ago
• Explosion produced the atomic particles that later formed galaxies, stars, and planets
• First stars probably formed 13 billion years ago
• The life span of a star depends on its mass
• Large stars burn up more quickly ~100,000 years
• Smaller stars, like the sun ~10 billion years
• A supernova signals the death of a star
• Release of huge amounts of energy

(Elements of the table come from exploding stars.)

Earth’s Place in Space: Where do the Elements Come From?

Nebular hypothesis– all bodies in the solar system formed from nebula.
• The Solar System formed from a rotating
cloud of gases and space dust about 4.6 billion years ago.
• This cloud, upon condensing, collapsed
under the influence of gravity and flattened into a rotating disk.
• The sun, planets, and moons formed within this disk.

Asteroids, Meteoroids

• Particles in the solar system are grouped according to
their size and composition
Asteroid
• 10 m – 1000 km in diameter
• Consist of rock, metallic material, or mixtures of the two
• Most are located in an asteroid belt between Mars and Jupiter
Metroid
• Smaller pieces of asteroids that range from dust to objects a few
meters across.

Meteor, Meteorite and Comet

• Particles in the solar system are grouped according to their size and composition
Meteor (usually blows up before hits ground)
• A meteoroid that has entered Earth’s atmosphere
• Emits light as it moves through the atmosphere
Meteorite
• A meteor that strikes the Earth
Comet (heats up by getting close to sun- how it gets its tail)
• Has a glowing tail of gas and dust
• Consist of a rocky core surrounded by ice and covered in dust
• Form outside the solar system in an area called the Oort Cloud.

Asteroids, Meteoroids and Comets

3 Classifications:
C-type: carbon
S-type: silicate rock
M-type: metallic – iron nickel
As long an asteroid remains in the asteroid belt between Mars
and Jupiter, it poses no hazard to Earth
An asteroid’s path can be disrupted by a collision
Path may then become elliptical and cross the
orbital path of Earth, in which case it is called a
near-Earth object.

Asteroids, Meteoroids and Comets

• Objects enter Earth’s atmosphere at 12 to 72 km/s (~7 to 45
mi per second)
• Metallic or stony
• Heat up due to friction as they fall through atmosphere, produce bright light and undergo changes
• Meteoroid will either
• Explode into an airburst
• Object explodes in atmosphere 12 to 50 km (~7 to 31 mi.)
• Ex: Tunguska
• Or collide with Earth as a meteorite
• If the object strikes Earth
• Concentrated in Antarctica

Airburst (pic)

Ex. Tunguska- 1908. Explodes before hitting ground, flattens surface.

Asteroids, Meteoroids and Comets

• Provide evidence of meteor impacts.
• Bowl-shaped depressions with upraised rim
• Rim is overlain by ejecta blanket
• Broken rocks cemented together into breccia
• Features of impact craters are unique from other craters.
• Impacts involve high velocity, energy, pressure, and temperature.
• Kinetic energy of impact produces shock wave into earth.
• Compresses, heats, melts, and excavates materials
• Rocks become metamorphosed or melt with other materials.

Asteroids, Meteoroids and Comets (3)

Impact craters are much more common on the moon for
three reasons:
1. Most impact sites on Earth are in oceans.
2. Impact craters on land have been eroded or buried.
3. Smaller objects burn up and disintegrate in Earth's atmosphere.

The Sudbury Basin- 1.8 billion years (pic)

Result of meteorite impact created nickels.

1. Simple Impact Craters

1.
• Typically, small (a few kilometers in diameter).
• Do not have an uplifted centre.
• Barringer Crater - Arizona.
(Raised rim, ejecta blanket)

2. Complex Impact Craters

2.
• Larger in diameter; can be 100 km
• Rim collapses
• The centre of the crater floor rises following the impact
• Most impact craters on Earth that are larger than 6 km are
complex

Minimizing the Impact Hazard

• Once a large near-Earth orbit object is known to be on a
collision course with Earth, options to avoid the effects
are limited
• Space guard Program
• Study Near-Earth objects with a diameter larger than 1 km
• Intercept the object and blow it apart.
• Small pieces could become radioactive and rain down on
Earth
• Divert the path of the object.
• Much more likely since we will have time to study the object
• We have the technology to change the orbit of an asteroid
• Small nuclear explosions would alter its path

Mass Extinctions

• The sudden loss of large numbers of species of plants and animals
• Coincide with boundaries of geologic periods or epochs
• Most hypotheses to explain mass extinctions involve rapid climate change caused by:
Plate tectonics
• Create new patterns of ocean circulation
Volcanic activity
• Large eruptions release huge quantities of carbon dioxide, warming climate
• Some eruptions release ash and Sulphur dioxide, cooling climate
Extraterrestrial impacts
• Release of dust blocks solar radiation
Climate Change

Mass Extinctions

• Geologists have documented five major mass extinctions during the past 550 million years
1. The first extinction could have been caused by global cooling
followed by rapid warming
• 446 million years ago
2. The Late Devonian mass extinction (365 million years ago) Life in shallow seas were the worst affected.
3. The Permian mass extinction (250 million years ago) The Great Dying
(2&3 also could've been volcanism too), chemistry in atmosphere.