The future of Europe hangs in the balance, the head of the European Parliament Martin Schulz said on Monday after euro zone leaders argued late into the night with near-bankrupt Greece at an emergency summit. "Today the European project is on a knife edge," Schulz, a member of Germany's Social Democrats (SPD), told Deutschlandfunk radio. "In Brussels, things are on a knife edge and the euro zone could fly apart," added Schulz, who said the SPD wanted Greece to stay in the euro.