Natural Hazards

Impacts and ExtinctionsChapter 14

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

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

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

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). Particles in rings attracted other particles and collapsed

into planets Earth was hit by inter-stellar debris, adding to its

formation Bombardment continues today

Anthropocene (human) epoch now?

Asteroids, Meteoroids, and Comets

Asteroids (10m –1000 km) - asteroid belt between Mars and Jupiter

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 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.

MeteorMeteorfully or partially vaporized on atmospheric entry

Meteoroid – smaller fragments

Asteroid - larger

Meteorite Meteorite Very small remnants that survive to land on earth

Figure 13.3

Oort cloud is extremely far away – most knowledge of it is inferential or theoretical

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 Metallic or stony Flash to flame on striking the atmosphere - bright light

Meteorites Small pieces that did not vaporize but instead survive to hit the

earth

Airbursts Meteor explodes on striking the atmosphere at high speed

(Tunguska 1908) Chelyabinsk (2013) included hundreds of meteorites large enough

to be collected.

Impact Craters Provide evidence of meteor impacts.

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. Impacts involve high velocity, energy, pressure, and

temperature. Kinetic energy of impact produces shock wave into earth.

Compresses, heats, melts, and excavates materials Soil and water may vaporize from vast heat produced by collision

Other rocks may metamorphose or melt.

Severity of meteorite impact:

Worst = vaporize into basic elemental gasesVery bad = completely melt into new rocksBad = metamorph into a modified rockNot 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:

Moon has no atmosphere to incinerate incoming objects

On earth, most impacts are in the ocean, buried, or erodedImpact 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/russian-meteorite . . )

Mass Extinctions Sudden loss of large numbers of plants and

animals

Sudden climate change

Define the boundaries of geologic periods or epochs

Mass extinctions can also be caused by meteorites and: Plate tectonics

Moves habitats to different locations Volcanic activity

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.

Dinosaurs disappeared with many plants and animals. 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? 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?

Iridium deposits indicate that layer formed quickly. Extinction probably caused by a single meteorite impact.

K-T Boundary Mass Extinction

Alvarez did not have a crater to prove the theory.

But we later found a crater in Yucatan Mexic0. 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.

Iridium metalBeautiful, 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)

Sequence of Events, cont.

Month later No sunlight, no

photosynthesis Continued acid rain Food chain stopped

Several months later 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. Occur once ever 40–100 million years

Smaller impacts are more probable and have their own dangers.

Linkages with Other Natural Hazards Tsunamis

Wildfires

Earthquakes

Mass wasting

Climate change

Volcanic eruptions

All of these events can result from a major meteorite strike on earth

Event Frequency and Risk Risk related to probability and consequences

Large events have consequences, will be catastrophic Worldwide effects Potential for mass extinction Return period of 10’s–100’s millions of years

Smaller events have regional catastrophe 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

This outlook is from the textbook and is being re-evaluated by scientists.

Risk Related to Impacts, cont.

Risk from impacts is relatively high. Probability that you will be killed by

Impact: 0.01%-0.1% Car accident: 0.008% Drowning: 0.001%

However, that is AVERAGE probability over thousands of years.

Events and deaths are very rare.

Emerging risk assessment may be altered upward:

Meteorite hazards to humans may be greater than we thought.

Minimizing the Impact Hazard

Identify nearby threatening objects. Spacewatch

Inventory of objects with diameter larger than 100 meters in Earth-crossing orbits

85,000 objects found so far Near-Earth Asteroid Tracking (NEAT or NEO) project

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

Small pieces could rain radioactivity down on earth

Nudge it out of Earth’s orbit 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

Bolide Meteor? Large enough to cause a sonic “boom”

Source: Astronomy.wonderhowto.com/inspiration/sonic-boom

Note the debris trail. The 1974 event also appeared to include visible flame and smoke

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>

Source: clarkplanetarium.org/venue/cosmic-light-shows

Impact craters

The planetarium also has very cool light shows set to rock music -- hah hah - no pun intended.

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 – 2013a 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.