A meteorite with a 1km diameter will undoubtedly cause global damage. It is believed that a meterite a bit larger was responsible for the extinction of dinosaurs. Rocks this big only appears to hit Earth once every 100 million years.
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It would catastrophic. Depending on the composition of the object, and where it hit, the effects would be "very bad" at a minimum, and "globe-altering" at worst. The impact would probably devastate any continent that it hit, and would likely cause earthquakes around the world. If it were to crash into the Indian Ocean, the tsunami would probably scour western Australia, eastern Africa, and most of India, and would inundate most of the middle east all the way to the Mediterranean Sea.
The "best" case might be an impact in Antarctica, which would not cause hundreds of millions of immediate fatalities, but probably would cause long term climatic changes including the worst components of "nuclear winter" and global warming; the Antarctic ice cap would probably melt substantially, and the debris thrown into the air would probably block most sunlight for a decade.
Fortunately, very rarely! Because those "intermediate" sized asteroid impacts do not cause global damage, we can't be entirely certain when in the distant past they happened. But not more often than every 3,000 years or so.
The last major impact may have struck in the southern Indian Ocean about 3500 years ago. Parts of western Australia appear to bear the marks of ancient inundations from the sea, and there is an interesting structure called the Burckle Formation on the floor of the Indian ocean. A tsunami generated by a large impact could easily have caused the hills we see today, and similar marks in India and Africa. Did I mention that this would also be a fairly good match for the legends of Noah and the Flood, or the Sumerian "Gilgamesh" epics? Many middle eastern cultures share legends of a major flood.
Before that, perhaps the impactor in northern Canada that correlates with the Younger Dryas mini-ice age, and the extinctions of most large life forms in North America about 14,000 years ago, including the Clovis People. Although at this point, we're well into the realm of speculation and conjecture, and have strayed from real facts.
However, there is a definite periodicity to major extinction events, about every 25 million years or so.
On average, a one-kilometer object hits Earth about once every few million years. These events are classified as rare but have the potential to cause significant damage if they were to occur.
NASA's Near Earth Objects program is one group that tracks object that pass near the Earth (you might have expected that from the name).
Probably Earth. It is assumed that in the very early life of the Earth it was hit by an object the size of Mars, resulting in matter ejected from the Earth, forming the Moon.
Chances are, no. There was some concern in 2004 that the asteroid Apophis might hit earth in 2029, but it is now known that the object will narrowly miss earth, though there is still some uncertainty of a few thousand miles as to how close it will come. There is still a very slight chance that it could hit earth in 2036.Even if we did predict that an asteroid would hit earth, we could not predict the path so precisely as to whether it would hit a particular city.
The object of the prepositional phrase "about dinosaur extinction" is "extinction".
Orbital ephemera. They consider its position relative to the sun, earth/moon, and other planets. Over a period of days they can determine its orbit, and whether that orbit likely intersects ours.