In the vast sweep of history, even an empire can be forgotten. In this wide-ranging talk, Gus Casely-Hayford shares origin stories of Africa that are too often unwritten, lost, unshared. Travel to Great Zimbabwe, the ancient city whose mysterious origins and advanced architecture continue to confound archeologists. Or to the age of Mansa Musa, the ruler of the Mali Empire whose vast wealth built the libraries of Timbuktu. And consider which other history lessons we might unwittingly overlook.

With what3words, Chris Sheldrick and his team have divided the entire planet into three-meter squares and assigned each a unique, three-word identifier, like famous.splice.writers or blocks.evenly.breed, giving a precise address to the billions of people worldwide who don't have one. In this quick talk about a big idea, Sheldrick explains the economic and political implications of giving everyone an accurate address -- from building infrastructure to sending aid to disaster zones to delivering hot pizza.

Margrethe Vestager wants to keep European markets competitive -- which is why, on behalf of the EU, she's fined Google $2.8 billion for breaching antitrust rules, asked Apple for $15.3 billion in back taxes and investigated a range of companies, from Gazprom to Fiat, for anti-competitive practices. In an important talk about the state of the global business, she explains why markets need clear rules -- and how even the most innovative companies can become a problem when they become too dominant.

The Greenland ice sheet is massive, mysterious -- and melting. Using advanced technology, scientists are revealing its secrets for the first time, and what they've found is amazing: hidden under the ice sheet is a vast aquifer that holds a Lake Tahoe-sized volume of water from the summer melt. Does this water stay there, or does it find its way out to the ocean and contribute to global sea level rise? Join glaciologist Kristin Poinar for a trip to this frozen, forgotten land to find out.