Natural Hazards
Impacts and Extinctions
Chapter 14
1972 – Great Daylight Fireball
Earth-Grazing Meteoroid – partially vaporized by continued on to a
subsequent close approach in 1999
Sources:http://science.slashdot.org/story and
http://www.phys.ncku.edu.tw/~astrolab/mirrors/apod_e/image/0903/earthgrazer_ansmet_big.jpg
If it partially burned in the atmosphere, then
shouldn’t it be called a ‘meteor’ instead?
I observed a smoke and debris trail that lasted
for many seconds.
Various Web sites also noted that.
Ok, now let’s review our learning objectives

Know the difference between asteroids, meteoroids, and
comets

Understand physical processes associated with airbursts
and impact craters

Understand possible causes of mass extinction

Understand the process of mass extinction caused by
extra-terrestrial collisions with earth
More learning objectives

Know the likely physical, chemical, and biological
consequences of impact from a large asteroid or comet

Understand the risk of impact or airburst of
extraterrestrial objects

Understand how impact risk might be minimized
Earth’s Place in Space

The universe may have begun with a “Big Bang” 14
billion years ago

First stars probably formed 13 billion years ago.

Lifetime of stars depends on mass

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Large stars burn up more quickly ~100,000 years
Smaller stars, like our sun may last ~10 billion years
Supernovas signal death of star

Releases energy and shock waves
Earth’s Place in Space

5 billion years ago, supernova explosion triggered the
formation of our sun.

Sun grew by buildup of matter from solar nebula

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Pancake of rotating hydrogen and helium dust
Hydrogen fuses into helium, releasing electromagnetic energy,
some of which is visible light.
After formation of sun, other particles were trapped in
rings (orbits).
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Particles in rings attracted other particles and collapsed into
planets
Earth was hit by inter-stellar debris, adding/subtracting its mass

Bombardment continues today
Anthropocene (human)
epoch now?
Asteroids, Meteoroids, and Comets

Asteroids (10m –1000 km) - asteroid belt between Mars and Jupiter

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Composed of metals
Meteoroids are broken-up asteroids
Meteors are meteoroids that enter Earth’s atmosphere
Meteorites actually hit the earth’s surface
Chondrite – a meteorite with more stone than metal - 85% of all
meteorites
Comets 


have glowing tails – dirty snowball
composed mostly of frozen water or carbon dioxide
May have originated in Oort cloud far from our solar system
Comets are soft - gas and/or ice.
Asteroids are rocky or metallic.
Meteors and meteorites travel at relatively high speed – collision
with Earth atmosphere causes immediate combustion:
intense heat and flame.
The energy of colliding with earth is converted to heat and flame.
Asteroid - larger
Meteoroid – smaller fragments
Meteor
fully or partially vaporized on atmospheric entry
Meteorite
Very small remnants that
survive re-entry and land
on earth
Oort cloud is extremely
far away – most
knowledge of it is
inferential or theoretical
Figure 13.3
Pluto has been relegated to
association with the Kuiper belt
Airbursts and Impacts

Objects enter Earth’s atmosphere at 27,000 to 161,000 mph
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Meteorites
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Metallic or stony
Flash to flame on striking the atmosphere - bright light
Small pieces that did not vaporize but instead survive to hit the earth
Airbursts

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Meteor explodes on striking the atmosphere at high speed (Tunguska
1908)
Chelyabinsk (2013) included hundreds of meteorites large enough to be
collected by people on the ground.
Impact Craters

Provide evidence of meteor impacts.
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Bowl-shaped depressions with upraised rim
Rim is overlain by ejecta blanket of debris
Broken rocks cemented together into breccia
Features of impact craters are unique from other craters.
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Impacts involve high velocity, energy, pressure, and temperature.
Kinetic energy of impact produces shock wave into earth.
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Compresses, heats, melts, and excavates materials
Soil and water may vaporize from vast heat produced by collision
Other rocks may metamorphose or melt.
A half-ton iron
meteorite was
found near Delta
Utah.
The “Upheaval
Dome” site south
of Moab may be
the dot on the
map.
Utah’s Upheaval Dome
Circular, with center uplift typical of an impact structure.
Or, could it just be a collapsed salt dome?
http://www.hohmanntransfer.com/cg/upheaval/dome.htm
Severity of meteorite impact:
Worst = vaporize into basic elemental gases
Very bad = completely melt into new rocks
Bad = metamorph into a modified rock
Not bad = be thrown into the air and broken
apart
Note: Being blown into the air and broken into
pieces is similar to a student not finishing an
ePortfolio before the final exam.
Simple
Impact
Craters

Typically small
less than 6 km

Arizona’s Barringer
Crater
A “shatter cone” may
form under the
impact zone.
Complex Impact Craters

Larger in diameter
than 6 km

Rim collapses more
completely

Center uplifts following
impact leaving a peak
Impact Rebound
Source: joerenaissanceman.blogspot.com
Impact Crater Details
Craters are much more common on the Moon because:
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Moon has no atmosphere to incinerate incoming objects
On earth, most impacts are in the ocean, buried, or eroded
Impact alteration of rocks can occur in collisions between asteroids
as well - - they hit each other - - a few are bumped toward the earth.
Intense heat and pressure may metamorphose rocks.
“Contact metamorphosis” can also occur on earth by tectonic force,
including volcanism and pyroclastics.
Add Chelyabinsk – 2013 – estimated 20-meters wide before exploding arrived at speed of 12 miles per second – 12 x 60 x 60 = 43,200 mph
Estimates of energy released vary widely, but
include:
-
A 7-meter (22 feet) wide meteorite striking the
atmosphere releases energy equivalent to an
atomic bomb.
-
5-meter meteors arrive about every year.
-
50-meter rocks arrive once a thousand years.
(Source: en.wikipedia.org/wiki/Impact_event
The Chelyabinsk meteorite event knocked people off
their feet. Others were seriously burned or even
blinded by the bright light of combustion.
The effects were much more than just breaking glass.
Scientists are now considering that impacts of that
size may occur more frequently than previously
believed.
(Source:www.theguardian.com/science?across-the-universe/2013/feb/15/russianmeteorite . . )
Mass Extinctions

Sudden loss of large numbers of plants and animals
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Sudden climate change

Define the boundaries of geologic periods or epochs
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Mass extinctions can also be caused by meteorites and:

Plate tectonics
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Volcanic activity
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Moves habitats to different locations
Large eruptions release CO2, warming Earth
Volcanic ash reflects radiation, cooling Earth
Changes in solar energy can also be attributed to
weather and/or catastrophic effect.
Six Major Mass Extinctions
1.
Ordovician, 446 million years ago (mya), continental
glaciation in Southern Hemisphere
2.
Permian, 250 mya, volcanoes causing global warming
and cooling
3.
Triassic–Jurassic boundary, 202 mya, volcanic
activity associated with breakup of Pangaea
4.
Cretaceous–Tertiary boundary (K-T boundary), 65
mya, meteorite impact
5.
Eocene period, 34 mya, plate tectonics
6.
Pleistocene epoch, initiated by airburst meteor,
continues today, more recently enhanced by human
activity
Now, consider that aside from earth change
caused by meteorites and volcanoes, human
power arose when the Pleistocene “ice age”
withdrew.
The earth warmed enough to provide space for
people to start farming and burning fossil fuel.
So, the “Anthropocene epoch” makes sense.
We are ‘human bulldozers” powered by ancient
solar energy stored for millions of years as oil,
coal and natural gas.
Let’s look a little more at the “K-T
Boundary Mass Extinction” 65 million
years ago.
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Dinosaurs disappeared with many plants and animals.
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70% of all genera died
Set the stage for evolution of mammals (humans are mammals)
What does geologic history tell us about K-T Boundary?
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Walter and Luis Alvarez decided to measure concentration of
Iridium in clay layer at K-T boundary in Italy.
Fossils found below layer were not found above.
How long did it take to form the clay layer?
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Iridium deposits indicate that layer formed quickly.
Extinction probably caused by a single meteorite impact.
K-T Boundary Mass Extinction
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Alvarez did not have a crater to prove the theory.
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But we later found a crater in Yucatan Mexic0.
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Diameter approx. 180 km (112 mi)
Nearly circular
Semi-circular pattern of sinkholes on land define the edges
Possibly as deep as 30–40 km (18–25 mi)
Slumps and slides filled crater
Drilling located breccia under the surface

Glassy, indicating intense heat
Notice the center uplift
– consistent with large,
complex crater.
Iridium is part of the platinum group – it is more
common in meteorites than in native earth.
Iridium rivals Osmium as the most dense natural
element known in the universe and the most resistant
to heat and corrosion.
Most of our Iridium may have come from a
meteorite. The Iridium ‘layer’ of rock points toward a
meteorite strike.
Some evidence suggests that the element nickel may also
have an extra-terrestrial origin.
Considering Iridium and possibly
Nickel, and the origin of the Earth’s
Moon, can we say?
1. The earth has accreted (added) mass from meteorite
strikes.
2. The Earth has lost mass due to meteorite strikes.
Can we also surmise that after billions
of years of hard meteor strikes and
planet formation, there may be less
mass available for strikes in the future?
Iridium metal
Beautiful, strong, expensive
Source: en.wikipedia.org/wiki/Iridium
Sequence of Events
a)
Asteroid moving at 30
km (19 mi) per second
b)
Asteroid hit the Earth,
producing a crater 200
km (125 mi) diameter,
40 km (25 mi) deep
c)
Shock waves crushed,
melted and vaporized
rocks
Sequence of Events, cont.
Seconds after impact:
•
•
•
•
•
•
Ejecta blanket forms
Mushroom cloud of dust
and debris
Fireball sets off wildfires
around the globe
Sulfuric acid enters
atmosphere
Dust blocks sunlight
Tsunamis from impact
reach over 300 m (1000 ft)
Ask yourself: “What role would
nitrogen play?”
Sequence of Events, cont.
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Month later
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No sunlight, no
photosynthesis
Continued acid rain
Food chain stopped
Several months later
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Sunlight returns
Acid rain stops
Ferns restored on burned
landscape
K-T Extinction, summary

Impact caused massive extinction of plants and animals,
but allowed for evolution of mammals.

Another impact of this size would mean another mass
extinction probably for humans and other large
mammals.

However, impacts of this size are very rare.
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Occur once ever 40–100 million years
Smaller impacts are more probable and have their own
dangers.
Linkages with Other Natural
Hazards

Tsunamis
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Wildfires
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Earthquakes
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Mass wasting
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Climate change
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Volcanic eruptions
All of these events can
result from a major
meteorite strike on earth
Event Frequency and Risk
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Risk related to probability and consequences
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Large events have consequences, will be catastrophic
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Worldwide effects
Potential for mass extinction
Return period of 10’s–100’s millions of years
Smaller events may create regional catastrophe
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This outlook is from
the textbook and is
being re-evaluated
by scientists.
Effects depends on site of event
Return period of 1000 years
Likelihood of an urban area hit every few 10,000 years

Local events every 100 years (Tunguska, Chelyabinsk)

Micro events – many daily
Risk Related to Impacts, cont.
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Risk from impacts is relatively high.

Probability that you will be killed by


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Impact: 0.01%-0.1%
Car accident: 0.008%
Drowning: 0.001%
Emerging risk
assessment may
be altered upward:
Meteorite hazards
to humans may be
greater than we
thought.

However, that is AVERAGE probability over thousands
of years.

Events and deaths are very rare.
Meanwhile, if the chances of getting hit by a
meteorite are greater than drowning, then why
don’t we have reports of human deaths from
meteorites?
Minimizing the Impact Hazard

Identify nearby threatening objects.
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Spacewatch
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Near-Earth Asteroid Tracking (NEAT or NEO) project

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Inventory of objects with diameter larger than 100 meters in
Earth-crossing orbits
85,000 objects found so far
Identify objects diameter of 1 km or larger
Use telescopes and digital imaging devices
Most objects threatening Earth will not collide for
thousands of years from discovery.
Minimizing the Impact Hazard

Consider our options once a hazard is detected

Use nuclear explosion to fragment the object in space

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Nudge it out of Earth’s orbit
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Small pieces could rain radioactivity down on earth
Much more likely because we will have time to prepare
Technology can change orbit of asteroid
Expensive process will require coordination of world military and
space agencies
Evacuation

A good idea only if we can predict impact point
Could be impossible depending on how large an area would need
to be evacuated

Notice that no personal preparation options are provided -

“Bolide” (fireball) Meteor
Perhaps large enough to cause a sonic “boom”
Note the debris trail. The 1972 event also
included visible flame and smoke
Source: Astronomy.wonderhowto.com/inspiration/sonic-boom
Do regular meteor ‘showers’
occur? Yes.
Lyrid, Geminid, Leonid and other regular
meteor “showers” occur, based on routine
intersection of orbits about the sun.
Comets exhibit similar habits.
Clark Planetarium at the Gateway
< The planetarium has a selection of meteorites and vast other resources for
ePortfolios>
The planetarium also has very
cool light shows set to rock
music -- no pun intended.
Impact craters
Source: clarkplanetarium.org/venue/cosmic-light-shows
Why does the “dark” side of the
moon have much more
cratering?
Because the moon’s rotation is
earth-synchronous,
so that it keeps the same face to the earth at all
times.
So, the side facing away from the earth is not
shielded from meteorites.
Chelyabinsk – 2013
a major meteorite strike in Russia
This meteor was tracked en-route to earth, supporting the concept of
prediction and protection
NEO and NEAT space programs are tracking other dangerous
asteroids and comets
Conclusion
Current science suggests that if an asteroid is large
enough to cause world-wide damage,
then there is probably enough time to identify the
hazard and take action at least 100 years before the
collision.