A member of an expedition group stands on the edge of a newly formed crater on the Yamal Peninsula, northern Siberia, on November 9, 2014. A group of scientists and discoverers went on an expedition initiated by the Russian Center of Arctic Exploration to research the crater after pilots captured it on video in July of 2014 which attracted the attention of world public.(Reuters/Vladimir Pushkarev/Russian Center of Arctic Exploration)
A member of an expedition group on the edge of a newly formed crater on the Yamal Peninsula, northern Siberia, on November 8, 2014. A group of scientists and discoverers managed to descend down to about 16 meters (52.4 feet) and reached the frozen surface of the base of the crater with a lake at least 10 meters (32.8 feet) deep below, according to Vladimir Pushkarev, head of the Russian Center of Arctic Exploration. Experts, including geologists and historians, have not come to a consensus about the origin of the funnel yet, Russian media report. (Reuters/Vladimir Pushkarev/Russian Center of Arctic Exploration)
Scores of riot police march to confront protesters near the airport in Mexico City on November 20, 2014. Protesters, some with their faces covered in masks or bandannas, scuffled with police as they tried to block a main expressway to the Mexico City international airport. Protesters hurled rocks and fireworks at the police, at least one of whom was hit by the projectiles. Protesters marched in Mexico City to demand authorities find 43 missing students on Thursday, a day traditionally reserved for the celebration of the country's 1910-1917 Revolution. (AP Photo/Marco Ugarte)
A motorcycle burns after protesters threw Molotov cocktails at riot police near the airport in Mexico City on November 20, 2014. (AP Photo/Marco Ugarte)
Joe Bernard, left, and Justin Sian kiss after being married at the Yellowstone County Courthouse in Billings, Montana, on November 20, 2014. A federal judge had just struck down the state's ban against gay marriage. (AP Photo/Matthew Brown)
A young Hong Kong couple who did not give their names wear gas masks as they pose for a wedding photographer prior to their marriage next to the tents used by pro-democracy demonstrators at the Admiralty protest site on November 14, 2014 in Hong Kong. (Kevin Frayer/Getty Images)