Financial markets on three continents sounded alarms Monday after Greece closed its banks in anticipation of a potential default on its debt and Puerto Rico announced it would be unable to pay back all of its $72 billion in debt, setting up a looming default of its own. Though separate events involving small economies, the twin debt crises exposed a new fragility in the financial system and came as a bit of a surprise to investors who had enjoyed relative tranquility in recent months.Read full article