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Some people have said that a meteor hitting the Earth is like a bug hitting the windshield of a car while the car is moving. The bug is so small and the windshield is so big that the bug just splatters. Yes, the bug makes a big mess, but the mess is all on the surface and doesn't affect the structure of the windshield or the interior of the car.

I believe that, while the bug hitting the windshield (BHTW) concept is too simplistic to describe what happens when celestial objects collide with the Earth, the windshield analogy can be employed to provide a picture of what does happen when objects collide with Earth.

There are three major factors that argue against the simplicity of the BHTW concept. These factors are:

1. The worst earth impacts are rocks, not bugs.

2. The speed of the impact objects is orders of magnitude faster (i.e. 24,000 mph vs. 60 mph).

3. The Earth's windshield is actually only its lithosphere (which is only 4 to 40 miles thick) rather than being the entire Earth, itself. Furthermore, the Earth is filled with liquid rock, the equivalent of having the car filled with liquid water, which would transfer the force if the windshield were deformed inwards or broken.

There are also the mitigating factors of the air in the atmosphere and the water on the surface of the arth, should an object happen to collide with Earth in a watery location.

Nevertheless, the BHTW concept can be modified to provide an easy, everyday understanding of what happens when cosmic objects collide with earth.

The first change to the BHTW concept is to change its name to the Rock Hitting The Windshield (RHTW) concept. The RHTW concept more accurately describes the severe nature of the worst cosmic impacts. When a rock hits a car windshield, the extent of the damage depends upon the size of the rock, the angle of impact, the hardness of the rock and the relative speed of the object, compared to the windshield.

When a small pebble hits a windshield, often there is no damage at all. Sometimes, depending upon the angle and speed of the pebble, a small pock mark might result.

The impact of a bigger pebble or a small rock may cause anything from no damage to a big pock mark with cracks propagating out into the rest of the windshield. The impacts of larger rocks and boulders can cause catastrophic damage, ranging destruction of the windshield to destruction of the car, itself. If the car had been been filled with water, the transferred energy would have blown out at least the rear window.

If a small rock were fired from a high speed rifle at 5000 mph, the effect would be similar to a high speed bullet … The windshield would be pierced and the rock would damage the interior of the car, as well. Most meteors hit the earth at speeds up to five times faster than a high speed bullet.

We can apply the RHTW concept to cosmic impacts. In effect, the Earth has its own windshield, called the lithosphere. This hard outer shell is 4 to 40 miles thick, depending where on earth it is measured. However, the thinnest sections of the lithosphere are located at the bottom of the ocean, where they are protected by miles of ocean water, which can greatly dissipate the effect of an impact.

Below the lithosphere, the Earth has various molten layers, which then culminate in the heavy solid core, which is composed mostly of iron. Regarding impacts, the important characteristic of these layers is the fact that two of them are not solid, but liquid.

Impacts on Earth's small hard shell with molten inner layers can have different effects, depending upon the size of the impact object, the angle of the impact, the hardness of the impact object and the relative speed of the impact object, mitigated by the effect of the air in the atmosphere and water at the impact site, if the object hits an area that contains a substantial depth of water (more than half of the Earth's surface is located under deep ocean water).

This list of impact factors sounds very much like the list of factors we examined with the RHTW concept. However, the size, speed and some other factors can be very different. Nonetheless, viewing the lithosphere as Earth's windshield can be a useful visualizing device.


Because of the interplay between the many factors involved in a cosmic collision, I believe that the best way to categorize impacts is to rate these impacts based upon their results, rather than upon how big the impact object was, how fast it was going or what the angle of impact was (among many other factors).

My Cosmic Impact Rating Scale goes from one to seven, with one being very minor and seven being the absolute obliteration of the planet.

1. GRADE 1 IMPACT—-Lack of Seismic Effect
A Grade 1 Impact is so minor that the seismic effect of the impact registers less than 3.0 on the Richter scale.

2. GRADE 2 IMPACT—Minor Seismic Effect
A Grade 2 Impact registers between 3.0 and 7.0 on the Richter scale as a seismic event.
The impact can be felt locally or regionally.

3. GRADE 3 IMPACT—Major Seismic Effect
A Grade 3 Impact registers more that 7.0 on the Richter Scale as a seismic event, but it does not transfer enough force through the molten layers of the inner earth to produce a volcanic eruption at the antipode (the spot on the exact opposite side of the Earth) of the impact site.

4. GRADE 4 IMPACT—Antipodal Volcanism
A Grade 4 Impact hits the Earth with so much force that the transfer of force through the molten layers of the Earth causes volcanic eruption at the antipode of the impact, resulting in what is known as a "hotspot." However, a Grade 4 Impact is not so great as to create continental uplift.

5. GRADE 5 IMPACT—Continental Uplift
A Grade 5 Impact imparts impact forces that are so huge that the impact not only forms a hotspot at the antipode of the impact site, but it also causes major continental uplift at and near the antipode. The usual shape of this continental uplift is "a blob with a tail." The volcanism at the antipode is extensive and can even result in some ejecta being thrown into space and (mostly) swept up by the Moon. However, a Grade 5 Impact is not so great as to create a major moon.

6. GRADE 6 IMPACT—Moon Formation
A Grade 6 Impact is so severe that ejecta is thrown into space and in orbit around the planet. The formation of our Moon is the only sure Grade 6 Impact that the Earth has ever experienced.

7. GRADE 7 IMPACT—Obliteration
A Grade 7 Impact erases the planet from existence.