Every recorded meteorite strike on Earth since 2,300 BCE mapped
osm2.cartodb.com
osm2.cartodb.com
I think "almost never" would be more accurate here.
Mercator is only used because it's the projection you get when you don't apply any projection to longitude/latitude. It's a result of the map creator being lazy.
I could equally well say it's lazy to use just use Google Maps or some other convenient mapping service that uses Mercator projections at the world level when those services are not really optimized for displaying at that scale.
Many orthogonal, North-aligned projections will look fairly similar same when zoomed into a street at least a couple degrees latitude away from the poles. Ideally, you would always use a 3D projection of that section of the sphere (e.g. Google Earth not Google Maps) or a local two-point equidistant projection since these are always the most accurate. An orthogonal projection only suffices in common usage because there is so little need for maps near the poles.
In any case, I should have qualified my original comment with: "for a whole-earth map or a map showing distributions". Mercator is always a bad projection for a map showing distributions because it seriously misrepresents area, undermining the effort to accurate portray distribution.
You see a lot of Google Mercator because it's the native projection of Google Maps and pretty much all subsequent slippy map libraries and tilesets. It's a great projection when you want something that works easily with map tiles and is zoomable. But it's not a great choice for a whole-earth visualization.
Some kind of explanation would be helpful, though. Apparently the size of the circle is related to the mass of the meteorite, and color is density of circles. But it took me a while to figure that out.
Also, what happened in Oman?
EDIT: Wikipedia says, "The central desert of Oman is an important source of meteorites for scientific analysis." Possibly meteorites are just easier to find there, due to properties of the terrain. Perhaps meteorite hunting is a popular sport/business, too?
Note the large number of strikes in the Sahara desert (and Antarctica, as someone else noted).
There are at least two things going on here, probably more:
1) Population density 2) Ease of finding the meteorite or crater (this is easier in barren areas with relatively homogeneous terrain, like the desert and Antartica).
In fact, the effects of 2) are reinforced even more, since my guess is that many, if not the majority of these findings were by scientific studies/surveys (note that they typically list the date found, not the date it occured). And since no one likes wasting their time, they would obviously pick areas where it would be easiest to find evidence.
One would expect the true distribution to be extremely uniform, right?
However, there could be a favoured plane of arrival, like the solar system plane, and with a circular cross section of the Earth I'd expect less debris/area near the poles. (I don't know this, I'm just extrapolating from what I actually know.)
As it turns out, Antarctica is a very productive place to look for meteorites, first because there isn't really a preferred geographical zone for meteorite impacts, and second because of the large, empty ice fields, against which newly fallen meteorites stand out.
One of the most famous meteorite finds of all time, ALH84001, was located by simply driving across the Antarctica landscape and watching for dark objects.
;)
Also notice: the only plotted strikes in Antarctica are right near the scientific stations -- but the intensity is very high at those points.
If you plotted theoretical meteorite distributions, there would be more strikes at the poles than the equator (due to the Earth's rotation, the poles receive many more meteorites) but at a given latitude the distribution would be even.
If you plotted theoretical meteorite distributions, there would be more strikes at the poles than the equator (due to the Earth's rotation, the poles receive many more meteorites) but at a given latitude the distribution would be even.
Could someone who understands this really well explain why the rotation of earth would change the number of meteorite strikes near the equator?
(It seems to me that strikes should be completely randomly distributed across the earth's surface and if a meteorite was headed for one area of the equator and the earth was spinning, the meteorite would simply hit another area of the equator.) I'm probably missing something here, but I can't figure out what.
Found some answers here: http://curious.astro.cornell.edu/question.php?number=746
Oh! The one that killed the dinosaurs. It was pretty big. Maybe only the big ones leave a mark on the ocean floor.