This Earth closely mimics the real Earth from between AD 1700 and AD 1750. The only two major differences are that most of its ancient cultures' myths were based more on fact than is presently believed, and a handful of its most significant historical figures were not actually human.
History of Earth's Isolation
Of all the worlds, Earth does the least communication and trade with other worlds. Only if absolutely necessary will it break its silence and embargo, and it will only do so away from the eyes of the majority of its inhabitants. This stems mostly from the rise of Christianity in the West and Islam in the Middle and Far East. Both religions regard any sapient non-human as demonic, and therefore evil. Thus, slowly, every other world housing a sapient species has voluntarily severed contact and trade for the safety of its people.
The rebirth of critical, rational thinking with the dawn of the Enlightenment brought hope to many that Earth would once again open its ports to rich, otherworldly trade, however this hope backfired when the lack of Charts to other worlds inspired the harshest of criticism from the Enlightenment's intellectual leaders. Without proof of these beings, rational thinkers dismissed even the possibility of their existence, much less the existence and value of their extra-terrestrial homelands. Hence the Enlightenment acted to hasten, rather than slow, the total isolation of Earth from the other worlds.
Present Inter-Worldly Status
Currently the Earth contains fewer Charts to other worlds than any other world, for the reasons outlined above. As such, it has become almost as much a place of myth in the common consciousness of other worlds as those worlds have become in the common consciousness of humanity, however the definitive existence of Charts to Earth keep the more extreme effects of this at bay. Very few sapient non-humans maintain residence on Earth, and most of those who still do are immortal one way or another and thus do not need contact with or supplies from any other world.
Earth is the most self-sufficient world, able to maintain its culture and lifestyle indefinitely without supplies or contact from any other world.