Chicago is the only airport in the United States, thus making the city of Chicago as well, that has direct flights to six continents. This makes this airport the best connected in the United States, offering direct flights to North America, South America, Europe, Asia, Africa, and Australia & Oceania. The only continent left to which there's no direct flight is Antarctica, with the reasons being the small interest, but much more the safety concerns as Antarctica is not the best place to have flights to considering its weather conditions. Chicago is actually only one of five cities in the world that has an airport that offers direct flights to six continents, being in the company of London, Dubai, Johannesburg, and Doha.
Except in the crust, the interior of the Earth cannot be studied by drilling holes to take samples. Instead, scientists map the interior by watching how seismic waves from earthquakes are bent, reflected, sped up, or delayed by the various layers.
