Earth is an island. When people say or think this they usually think of the Earth as a sensitive but contained system. One has to remember, however, that islands are repeatedly battered by waves and sometimes a massive storm can change the whole ecosystem.
Case in point is this map from Earth Sky which shows the current (February 13, 2013) meteor, asteroid, comet giant space rock, whatever traffic Earth has to navigate. And this is just the space debris we know of.
|Click to enlarge.|