The Science of Game of Thrones

Shortly after the end of the Pleistocene epoch in a parallel universe, a comet impacted with the Moon. The resultant meteor shower of large chunks of the Moon drastically altered the geography of the Earth. Although the comet impact did not completely shatter the Moon, it did destroy enough of the Earth's satellite to significantly decrease its size. A gravitational effect of the smaller Moon is that the Earth's rotational axis has been permanently destabilized. Because of that, the planet has inconsistent and unpredictable seasonal lengths. The altered planetary geography (which includes extremely large oceans, an abundance of gigantic mountains, exceptionally strong currents and extremely powerful prevailing winds) also contributes to the creation of the unpredictable weather trends. Along with the altered geographical landscape, another effect of the meteor was a brief but considerable disruption of the stratosphere's blocking of cosmic radiation. During that disruption, the bombardment of radiation caused various mutations to take place amongst life on Earth. Animals that arose include direwolves, shadowcats, dragons and krakens. Even new plant life such as weirwood trees arose. Humanity was also effected. From the mutations arose new human races such as the Children of the Forest and the White Walkers. A benevolent mutation that spread among all humanity was the capacity to mentally summon entities from extra-dimensional realms in order to manipulate and alter reality. Known as "magic" this capacity was especially strong in the Children of the Forest. This is the Earth in which the continents of Westeros and Essos exist and which the War of the Five Kings are fought.