Impact Hazards

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.

  1. 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 coast.

  2. 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 waters.

  3. 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 the cooling.

  4. Eventually, the dust will settle to the ground, sunsets will be spectacular, but nothing will be around to enjoy them.

More 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 website.


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.

Perhaps 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 American.
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 Foundation.

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 Introduction.

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