PHYSICAL GEOLOGY
Meteorite Impacts
Name ________________
Period ___ Date_______
© E. Fermann, 2008
Barringer Meteorite Crater
Photo credit: David Roddy, USGS
Materials
This lab
Internet connection
Microsoft Excel
Google Earth
Introduction
A meteorite is a solid object found on Earth's surface after it entered Earth's
atmosphere from interplanetary space. Meteorites are classified into different types based
on their mineral composition and on the presence or absence of chondrules.
Chondrules are spherical aggregates of minerals, usually olivine or pyroxene. Scientists
believe chondrules formed by the crystallization of a droplet of silicate melt.
(Source: http://research.amnh.org/earthplan/collects/metegrp.html)
Meteorite Impact Frequency
One approximation places the number of meteorites that land on the earth every year
at about 26,000. Most of these are, however, very small. Meteorites with diameters of
about 1 mm strike the Earth about
once every 30 seconds. Upon entering
Earth's atmosphere the friction of
passage through the atmosphere
generates enough heat to melt or
vaporize these objects, resulting in socalled shooting stars. Larger
meteorites strike Earth less frequently,
but may only partially melt or vaporize
on passage through the atmosphere,
and thus may strike Earth’s surface.
Objects with sizes greater than 1
km are likely to produce catastrophic
effects. Such impacts occur relatively
infrequently -- a 1 km sized object
strikes Earth about once every million
years, and a 10 km sized object strikes
Earth about once every 100 million
years.
Meteorite Impact Effects
Looking at the surface of the Moon, one is (or
should be) impressed that one of the most common
surface features of the Moon are impact craters.
The Earth is subject to more than twice the amount
of impacting events than the moon because of its
larger size and higher gravitational attraction. Yet,
the Earth does not show a cratered surface like the
moon. The reason for this is that the surface of the
Earth is continually changing due to processes like
erosion, weathering, tectonics, sedimentation, and
volcanism. Thus, the only craters that are evident
on the Earth are either very young, very large, or
Lunar Craters, NASA
occurred on stable continental areas that have not
been subject to intense surface processes. There are
approximately 200 terrestrial impact structures
which have been identified, with the discovery rate of new structures in the range of 3-5
per year.
The effects of an impact by an object with a size greater than about 1 km would be
likely to be felt over the entire surface of the Earth. Smaller objects would certainly
destroy local ecosystem in the same way that a volcanic eruption would, but larger
impacts could have a worldwide effect on life on the Earth.
Humans have never observed impacts of large meteorites (thank goodness). Much of
our knowledge about what happens from such an event must come from scaled
experiments or computer models. Dr. Jay Melosh (from the University of Arizona) has
created a web site that can be used to predict the crater size and effects from various
meteorite impacts. In this lab, you will use this web site and the program Excel to create
a graph that relates the diameter of a meteorite to the crater size it would create.
Meteorite Classification
There are several types of meteorites. They include the three basic categories of stones,
irons, and stony-irons. Each has a different composition, density, and relative abundance in
the solar system.
Stone (stony) Meteorites
Stone meteorites make up approximately 94% of observed falls and are thought to be
material from mantle and crust areas of asteroids. Stony meteorites contain approximately
75-90% silicate (stony) minerals (mostly olivine and pyroxene) and 10-25% nickel-iron
metal and iron sulfide. Some stone meteorites are believed to have originated from other
planets, especially Mars.
Iron Meteorites
Iron meteorites are composed almost entirely of nickel-iron. They often have mineral
inclusions and are believed to originate from the core of large asteroids. Approximately
4.8% of all meteorites are irons.
Stony-Iron Meteorites
Stony-iron meteorites are composed of approximately 50% nickel-iron and 50% silicate
material. They make up only 1 to 2% of all meteorites.
Directions
1. Go to the internet web site developed by Dr. Jay Melosh (Univ. of Arizona)
http://www.lpl.arizona.edu/impacteffects/ and get yourself oriented. There are
several parameters you will need to manipulate before you estimate the crater size of
a particular meteorite.
Parameters
A. Distance from impact – this has no effect on the size of the crater, but choose a
distance about 200 km away (That’s just a little farther than the distance from
here to Philadelphia).
B. Projectile Diameter – This is the one you will want to vary…start with a
diameter around 100 meters (about as large as a football field).
C. Projectile density – Choose the dense rock (3000 kg/m3) option from the pull
down list. We will use this one because it is most like the majority of meteorites,
the stony irons.
D. Impact Velocity – Use the ‘typical’ velocity of 17 km/s.
E. Impact Angle – Use the most probable angle of 45 degrees.
F. Target Parameters – Since much of Earth’s surface is covered with sedimentary
rock, select sedimentary rock.
When you finish entering the first set of parameters, select ‘calculate effects’ at the
bottom of the page. Read through the effects that this impact would create.
a.
b.
c.
d.
e.
f.
g.
How much energy is released? _______________
Does the meteorite reach the ground in one piece or broken up? ________
At what altitude would the meteorite begin to break up? ____________
Does this meteorite shift the Earth’s axis? _________
How large is the final crater from this impact? __________
What earthquake magnitude would this impact create? ________
What would the impact feel like (Mercalli Index) to someone 200 km away?
________________
h. Would you be able to hear this impact 200 km away? ________
Impressive, no? Just wait until we get to larger meteorites!
2. Create a graph of the data you have collected. Go to the shared Fermann folder and
open the document called Impact.xls. Save a copy of this file to your folder using an
appropriate name. (mine might be: fermann_impact.xls).
Run the Impact Effects calculator on the website we were just looking at several
more times while changing the projectile diameter between 1 meter and 10,000
meters (10 km). Keep all the other parameters the same. Complete the data table on
the Excel sheet. As you complete the table, graphs will be produced.
Print out your graphs and include them with this lab.
Questions:
1. What size crater would result from the impact of a 5000-meter diameter stony iron
meteorite with the Earth?
2. Approximately how often would you expect such a crater to be formed on Earth’s
surface? (Refer back to the figure on pg. 1)
3. According to the graph on page 1, a meteorite with a diameter of 1 meter strikes
Earth’s atmosphere approximately once each year. What effects would you expect
this ‘yearly event’ to produce?
4. Think about the moon’s surface... Explain why there are so many more craters on the
moon’s surface than on Earth’s surface. Hint: think about geological processes.
5. The Barringer Meteorite Crater in Arizona (see the picture at the top of this lab) is
nearly a mile wide, and 570 feet deep. If the meteorite responsible for this crater was
a stony meteorite, how large must it have been? What effects would this impact have
had locally? Globally? (Maybe re-run the web-program once you know the meteor
diameter…)
6. The Cretaceous Extinction (66 million years ago) was thought to have been at least
partially the result of a meteorite impact that altered the Earth’s climate. The impact
crater for this meteorite is believed to have been found off the coast of what is now
Mexico (see figure to the below).
http://www.student.oulu.fi/~jkorteni/space/boundary/yucatan.jpg
How large would the meteorite have been to create a crater this size? (you might need to
estimate or play with the web-program)
7. How would this meteorite have impacted the Earth’s atmosphere?
8. Open the Google Earth Impact.kmz file from the shared geology folder. “Fly
around” for a bit from crater to crater to see some impacts. Choose three impact
locations and complete the table below. Use the measure tool in GE to measure the
crater diameter.
Inferred Size of
Impact Name
Age of Impact
Crater Diameter
Meteorite
9. Why some craters clearly visible and others are are VERY difficult to see?