what are the causes of impact craters?
111889
Ummm...impacts?  :)\n\n"An impact crater (impact basin or sometimes crater) is a circular depression on a surface, usually referring to a planet, moon, asteroid, or other celestial body, caused by a collision of a smaller body (meteor) with the surface."
149121
Soddy is an eroded lunar impact crater that lies to the south-southeast of the prominent King crater. Material from the ray system surrounding King covers the sides and interior of Soddy crater. Less than a crater diameter to the west of Soddy is the smaller Heron crater.\n\nThis crater has been heavily worn and eroded, so that only a remnant of a crater depression survives. There are small craterlets along the rim edge to the southwest and southeast. The interior is uneven and almost indistinguishable from the surrounding terrain.\nhttp://en.wikipedia.org/wiki/Soddy_%28crater%29
423720
Sure, in simple terms the main theory right now is that of a large meteoritic impact, proposed back in 1980.  It fits the requirement of a rapid and sudden kill-off event.  What killed the dinosuars?  Well the immediate effect of a large asteroid impact would be global firestorms.  The ejecta reaches low earth orbit and then superheats as it re-enters the atmosphere.  This pretty much covers much of the planet in fire.  Other bad things happen, toxic metals in the air and water, dust obscuring the sun, many bad things, but the main killing factor is the global fire storm.\n\nAs scientists we really like the asteroid impact theory as it is supported with the following eveidence (I have not heard any serious arguments about a double impact by the way):\n\n1. The boundry layer in which the extinction occured is ultra-rich in the element irridum.  These irridium levels are not found on earth, but match very well to those of meteoritic samples that we have.  This boundry layer with irridium has been found all over the globe.\n\n2. Shocked quartz deposits have been found in the regions near central to lower north america, indicating a large shockwave propagated across the area\n\n3. Tiny glass beads have been found in the same regions, with larger ones more concentrated near the Yucatan.  Thes glass bead are most closely related to objects we call Tektites, glass that forms from meteorite impact ejecta.  (cool science thing: you can get tektites for a couple dollars at any rock shop!)\n\n4. Tsunami deposits from that era have been found in the gulf of mexico region, indicating massive tidal wave events\n\n5. A crater caused an impact large enough to cause all of these things has been found right on the coast of the Yucatan, centered on Chicxulub, and dating to the right time period.
91362
It's tranferred to heat/friction from the impact
460102
Depends on the size of the comet, many just disintegrate on the atmosphere. A really big one could create:\nShift in the orbit, heat from the explosion, smoke and dust from the explosion covering the Sun. Earthquakes and volcanic eruptions from shift in magnetic field due to orbit shift. Basically extinction of many forms of life, possibly even human.
437156
Sure, the main theory right now is that of a large meteoritic impact, first seriously proposed back in 1980. It fits the requirement of a rapid and sudden kill-off event. What killed the dinosuars? Well the immediate effect of a large asteroid impact would be global firestorms. The ejecta reaches low earth orbit and then superheats as it re-enters the atmosphere. This pretty much covers much of the planet in fire. Other bad things happen, toxic metals in the air and water, dust obscuring the sun, many bad things, but the main killing factor is the global fire storm.\n\nAs scientists we really like the asteroid impact theory as it is supported with the following evidence:\n\n1. The boundry layer in which the extinction occured is ultra-rich in the element irridum. These high concentrations of irridium are not found on earth, but match very well to those of meteoritic samples that we have. This boundry layer with irridium has been found all over the globe.\n\n2. Shocked quartz deposits have been found in the regions near central to lower north america, indicating a large shockwave propagated across the area\n\n3. Tiny glass beads have been found in the same regions, with larger ones more concentrated near the Yucatan. Thes glass bead are most closely related to objects we call Tektites, a glass that forms from meteorite impact ejecta. (cool science thing: you can get tektites for a couple dollars at any rock shop!)\n\n4. Tsunami deposits from that era have been found in the gulf of mexico region, indicating massive tidal wave events\n\n5. A crater caused an impact large enough to cause all of these things has been found right on the coast of the Yucatan, centered on Chicxulub, and dating to the right time period.
86914
It's probably all land - some lowlands, some highlands, *LOTS* of craters.
85952
(You probably mean NON-terrestrial planets.)  Craters (whether you mean meteor craters or valocanic craters) on earth are less evident because they are constantly being eroded by weather effects such as wind, rain including floods, and geological activity such as volcanoes and plate tectonics.  The moon for example, does not have any of that, so the only thing that might make meteor craters less evident is another later meteor strike.
320584
Yes, it's only a matter of time.  Scientists are finding more and more places on Earth that are actually meteor craters.  They have found that Meteor Crater in Arizona actually was created by one, that a large valley in Germany is actually a large meteor crater, that the dinosaurs were killed off when a meteor hit the Yucatan peninsula, etc., etc.  The only reason they don't show up as well on Earth is because of erosion.  But if there is shocked quartz nearby, a meteor has hit, because it is not found naturally, but is caused by a meteor strike.  There are hundreds, if not thousands, of orbit-crossing meteors, so it is only a matter of time before another one gets us.
754417
a sudden break in the rocks of Earth because of being stressed .. at depths range from the earth surface to 720 km .. this releases kinetic energy which spreads in every direction as seismic waves wich cause the vibration of the molecules of the meduims they move through !!!
79281
It is thought that an object the size of Mars impacted with earth and created the debris that colesced into the moon.  I'm not sure that this impact is thought to have brought life to Earth, but other impacts from comets and meterorites that contain complex proteins or simple microbes could be the answer.  try reading "A Short History of Nearly Everything" by Bill Bryson for more detail.
360341
We have an atmosphere and weather.  That is always changing the surface of the earth.  Erosion takes place and over time things flaten out.\nIn other cases the craters are still there, they just happen to be so large the only way we see them is through pictures from satellites.  The vegitation also help mask the craters
561205
D. Fissure eruptions\nand it also happens mostly under water.
1067986
The Tunguska Event.\n\nA huge non-nuclear, sub atomic explosion in the skis over Siberia. \n\nThe theories around the cause of the explosion are varied;\n\nStray Anti-Matter particle.\nComet/ Meteor overheating and exploding on entry.\nSolar Particle disruption caused by mass sunspot activity.\nBy product of a Solar Mass Ejection event. \nA Primordial Black hole.\n\nOne theory I read stated that according to the "math" the instantaneous opening and collapse of a wormhole would release the same amount of energy.\n\nAny way, it happened in 1906, but a "rescue" mission wasn't sent for 10 years because at the time that part of Siberia was so remote they had to build railways roads and bridges to get there.
762290
Water...\n\n* Liquid water, eg in rivers and coasts (in the sea this is largely caused by the gravitational effect of the moon);\n* Liquid water is a major cause of landslides - soil becomes over-saturated and therefore loses its adhesion to the soil or rock beneath;\n* The action of freeze-thaw where liquid water seeps into cracks, expands when it freezes thereby widening the crack and ultimately splitting rocks apart;\n* Frozen water in the form of glaciers grinding away at mountains;\n\nOther causes of erosion include:-\n* the wind, especially when it blows sand particles with it which erode rocks;\n* the Sun which alternatively heats and cools rocks so that they split in much they same way as freeze-thaw (especially in desert areas);\n* humans - we contribute to many of the above processes by our own actions, eg deforestation prevents the soil from holding as much water so landslides become more likely; over-farming creates deserts which are subject to wind and sun; coastal "management" often results in more rapid erosion of some areas of coastline
849034
Yes, when a comet or Meteor hits the atmosphere the pressure of the air and speed of the object causes the object to expand so rapidly that a hugh explosion occurs.\nthere was one in 1908 in Tunguska Siberia which flattened trees for thousands of miles\nand the shockwave was detected in London\n\nhttp://www.psi.edu/projects/siberia/siberia.html\nhttp://www.world-mysteries.com/dougy_tunguska.htm\nhttp://www.doomsdayguide.org/Mystery/unexplained_tunguska.htm\nhttp://www.themystica.com/mystica/articles/n/nuclear_tunguska.html
760730
Rays.  Rays are composed of ejecta from the impact, tend to be intrinsically brighter than the surrounding material and also scatter light differently.  They are relatively brighter at full moons (they tend to preferentially back scatter light towards the source better than the surrounding soil.)