The tusk of a woolly mammoth that lived some 18,000 years ago, from which researchers sequenced the extinct mammal's entire genome, is seen in northeastern Siberia in this photo from 2015. (Photo by Love Dalen/Handout via Reuters)

Fire fighters, emergency service vehicles and a helicopter in Moskovsky Prospekt at the entrance to Tekhnologichesky Institut station of the St Petersburg metro in the aftermath of an explosion which occurred in a train at 14:40 Moscow timeon April 3, 2017. (Photo by Peter Kovalev/TASS)

Revellers take part in an annual block party known as “Cordao de Prata Preta”, one of the many carnival parties to take place in the neighbourhoods of Rio de Janeiro, February 6, 2016. (Photo by Pilar Olivares/Reuters)

A visitor takes pictures with a smartphone of an artwork entitled “Blue Europe, 2015” by Chinese artist Liu Bolin, on display during the exhibition “Visible Invisible” at the Mudec Museum in Milan on May 14, 2019. Liu Bolin known as “the invisible man” for his photographic self-portraits, focused on a body-painting blending with the surrounding area. (Photo by Miguel Medina/AFP Photo)

In this photo taken Saturday, June 20, 2015, Mahmoud Abdulnabi tries out an oud, an Arabic instrument related to the lute, at his workshop in Baghdad, Iraq. “The oud is different than other musical instruments”, said Abdulnabi, who has crafted ouds played by some of Iraq's best known musicians, many of whom look down from headshots on the walls. “If you feel joyful, it can play your joy. If the circumstances are sad it can play your sorrow and... help to empty whatever is in your chest”. (Photo by Hadi Mizban/AP Photo)

Libya's leader Muammar Gaddafi attends a meeting with Italian President Giorgio Napolitano at the Quirinale Palace on June 10, 2009 in Rome, Italy. Colonel Gaddafi is in Rome to attend a meeting of G8 Development Ministers. (Photo by Franco Origlia/Getty Images). ROME – JUNE 10

A man poses for a picture to show his rings of gold, silver and bronze on his fist in Zamfara, Nigeria April 21, 2016. (Photo by Afolabi Sotunde/Reuters)