There is nothing more fearsome for the Earth than for a large rock from space
to hit us. You have learned from the Meteorite page that large rocks repeatedly
strike the surface of the Earth, but in this section of the course we are looking
at really, REALLY BIG rocks. Rocks that are greater in diameter than 10,000
m or 10 km. These rocks lead to global extinction of life and pose the most
incredible threat of all. Whether such rocks hit the ocean or land, the results
are always catastrophic. To begin this page, please look at the diagram below
that clearly shows the geologic extinction events in the past 500 million years.
Other giant impacts must have happened in the more distant past, but life was
only at the single cell level prior to 700 mybp that their events are not recorded
here. The purpose of showing you this chart is to make you aware that Earth
has been hit by large rocks in the past, and will doubtless get hit again ...
but when is anyone's guess.
What can we expect if a rock greater than 10 km in diameter were to strike our
world? Here is a scenario of the sequence of events:
The incoming asteroid or comet nucleus would probably enter the atmosphere
at 66,000 miles per hour. This is the orbital velocity of the Earth, and since
it is most likely that Earth will run into the straying object, that then becomes
the speed of entry. This extreme velocity will generate a huge wave of compressed
and superheated air around the inbound object. The result is incineration for
many square miles of anything near the superheated air.
The rock will strike the Earth either in the ocean or on land. If the
rock hits the land, then a huge explosion from the inbound rock will transfer
energy of impact into outward explosive force and a shockwave of great power
will travel outward at tremendous speed. Whatever has not been incinerated
by the superheated air will be knocked over by the shockwave for a distance
of hundreds of kilometers. If the rock hits the ocean, then a shockwave
of energy will travel outward as forceable air and a giant tsunami. Some
scientists predict a tsunami rising to a height of 1500 meters or more ...
IN THE MID-OCEAN. The wave gets MUCH higher as it nears the coast. Whatever
is not knocked down by the shockwave of air will be wiped out by the giant
tsunami and tidal wave that would certainly wash well inland from any continental
The explosion will throw huge amounts of rock and dust high into the upper
atmosphere of Earth. The larger rocks in the mushrooming cloud will fall
back down and destroy things they will land upon. The smaller particles
will remain in the upper atmosphere and quickly scatter over the entire
globe. The result of this vast dust cloud is the real threat from the impact.
The cloud will darken the sky on a completely global scale and photosynthesis
will cease. Within a few days, phytoplankton will die. A short time later,
trees and grasses will die. With no more conversion of water into oxygen
by planets, small animals will perish in a few weeks. After a month or two,
every living organism will be dead ... on the land, in the air, and in the
The dust cloud will bring about extreme global cooling in an event called
"nuclear winter." This will last for 6 months to 3 years according
to different scenarios. Oceans will not necessarily freeze, but whatever
organisms that found some form of shelter underground might not survive
Eventually, the dust will settle to the ground, sunsets will be spectacular,
but nothing will be around to enjoy them.
Impact Details explores the potential catastrophe of a major strike, and
also proposes plans to locate potential impactors. To see that the US government
is doing about these threat, go to NASA
Asteroid site, click on the Earth-Target site and browse around. To see
how Asteroid Destruction
can be accomplished by an Empite Star-Destroyer, go to this cute webpage. To
look more closely at the Cretaceous Period ending event that probably killed
the dinosaurs, check out the KT
On April 23, 2004, I received my edition of Science magazine. In the early
parts of the magazine was a small article that offered an opportunity to use
a noew tool developed by the University of Arizona. The short article reads,
"Space chunks the size of a basketball slam into Earth more than once a
month, whereas boulders big enough to level Manhattan hit about every million
years. This new calculator
from researchers at the University of Arizona, Tucson, lets you determine the
destructive power of such collisions. It estimates the blast's impact from variables
such as the size of the object, its trajectory and composition, and your distance
from ground zero. For example, an iron-rich meteorite 10 meters in diameter
landing 20 kilometers from your home would rattle windows and produce a boom
as loud as heavy traffic. An object 1 kilometer across -- about one tenth the
size of the asteroid that snuffed out the dinosaurs -- falling the same distance
awayt would wrench and topple buildings; the resulting fireball would severely
burn anyone in your neighborhood, just before a shower of debris buried them."
To date, very little is being done to thwart a potential giant impact. Asteroids
that cross the Earth's orbit are called Near
Earth Objects (NEO's) or Near Earth Asteroids (NEA's). A few people are
dedicating their spare time to looking for asteroids that could pose a threat,
but there are many out there, lurking in the dark of space, that have not yet
been discovered. To look at the probability
of Earth being hit, check out the webpage and lose a lot of sleep at night.
Best of all is an entire site devoted to Catastrophism,
and this place explores everything bad about large impacts. I put the little
Andromeda image next to the Catastrophism site because it really is excellent
and worth some of your time.
you are now extremely concerned about this threat from space. Perhaps you are
even becoming paranoid, fearing that you might get hit while driving in your
car, or while out on a run, during a midnight's sleep, whatever. What can you
do to give yourself a sense of calm amid the impending disaster, be it great
or small. Well, I think you need to get some Asteroid
Insurance. This website is your opportunity to purchase a policy that will
restore your home, car, and other belongings should a rock from space come crashing
down on your dwelling. Apparently, all this policy costs is $19.95 plus a nominal
$3.00 fee for shipping and handling. There is another group that offers several
Asteroid Insurance Options
for those who want more than a general policy. This company has plans like The
Acopalypse Plan, The Catastrophe Plan, The Disaster Plan, and the Tragedy Plan.
What more can you want, you might ask? Well, there is a company that even offers
Alien Abduction Insurance :)
Okay ... so all of these little companies are gimmicks and pure humor, but
it still is interesting that someone had the creativity to generate these websites.
I wonder how many people have stumbled upon these places and plunked down money
without thinking about the insanity of it all. What good is an insurance policy
after a global extinction event?
Here is a suggested activity that helps you see the impact craters on the
Earth, and then do the activity to determine What
Killed the Dinosaurs?
Why be at the mercy of a menacing asteroid that has Earth in its cross hairs?
Now an expert team of astronauts and space scientists has blueprinted a safety
strategy for Earth: an asteroid tugboat. The group says NASA is already working
on the right recipe of technologies to make the tug a reality. It would be the
greatest public safety project in history. Furthermore, they propose a mission
to demonstrate the asteroid-tug concept by 2015.
Details of the asteroid tug are unveiled in the November 2003 issue of Scientific
Lead author of the article is former astronaut, Rusty Schweickart, Apollo 9's
lunar module pilot that put the Moon landing craft through its paces high above
Earth in March 1969. Other contributors are Piet Hut, Professor of Interdisciplinary
Studies at the Institute for Advanced Study in Princeton, New Jersey, and asteroid
specialist, Clark Chapman of the Southwest Research Institute here in Boulder.
The team has proposed a spacecraft designed to rendevous with a potentially
dangerous asteroid, attach to it, and then ignite thruster rockets to nudge
the asteroid out of the Earth's direction. The spacecraft and rendevous is shown
below left and right. To learn more about this mission program, click on B612
Now, you can go to see a little idea about what to do
with a near-Earth Asteroid ... mining.
Or you can move back to Asteroids, or the Planet
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