Markets sunk sharply from the off on Thursday morning as the FTSE 100's losing streak was extended into its fourth day, with RBS in focus after shocking the City with the surprise resignation of Chief Executive Officer (CEO) Stephen Hester. Following the impressive rise seen at the start of the year, recent market volatility has hit the FTSE 100 - and indices across the globe - hard over recent weeks, with London's benchmark index now trading down at levels not seen since late January. Including this morning's slump, the Footsie's year-to-date rise has now been trimmed to around just 5.5%.Continuing uncertainty regarding the Federal Reserve's 'exit strategy' from stimulus and a strengthening yen saw Japan's Nikkei index plummet over 6.0% on Thursday, while China's Shanghai Composite and Hong Kong's Hang Seng lost nearly 3.0% of their value. "Despite the fact that it remains unlikely that either the Fed or the Bank of Japan are likely to start reining back on their stimulus measures any time soon, investors appear to have decided that the mere prospect of an exit strategy is enough of a reason to look at pulling money off the table on a fairly comprehensive scale," said Senior Market Analyst Michael Hewson from CMC Markets.Markets were also hit yesterday by renewed fears about political tension in Greece following reports of an emergency cabinet meeting in Greece and rumours of a potential vote of confidence for Prime Minister Antonis Samaras.Dampening sentiment further was the World Bank which yesterday cut its forecast for global economic growth to 2.2% in 2013, down from its initial 2.4% estimate in January. Meanwhile, the bank said it now expects China to grow by just 7.7% this year, down from its previous 8.4% prediction.RBS in focus as Hester steps downAs expected, RBS tanked early on after announcing late last night that Stephen Hester will step down as CEO after five years. The boss, praised widely for his work for turning the bank around following its government bailout in 2008, said he was stepping aside as the lender prepares for a re-privatisation. Meanwhile, according to Sky News City Editor Mark Kleinman, RBS is to announce plans to cut up to 2,000 investment-banking jobs as part of its ongoing restructuring.Sector peers Barclays, Lloyds, HSBC and Standard Chartered were also in the red. Homebase and Argos owner Home Retail slumped early on as both chains suffered a decline in margins in the first quarter. Nevertheless, CEO Terry Duddy said that overall the group's trading has been consistent with the board's expectations.Luxury fashion group Mulberry gained after revealing full-year results in line with expectations, with revenues up 8.0% to £107.2m.Retail WH Smith fell after saying that sales in the third quarter were down 5.0%, while like-for-like sales fell by 6.0%.FTSE 100 - RisersUnited Utilities Group (UU.) 729.50p +0.21%Petrofac Ltd. (PFC) 1,263.00p +0.16%FTSE 100 - FallersRoyal Bank of Scotland Group (RBS) 305.40p -6.20%Aberdeen Asset Management (ADN) 387.70p -3.68%Old Mutual (OML) 179.10p -2.77%Barclays (BARC) 288.25p -2.55%GKN (GKN) 292.60p -2.47%Evraz (EVR) 110.90p -2.46%Schroders (SDR) 2,102.00p -2.23%easyJet (EZJ) 1,187.00p -2.22%Lloyds Banking Group (LLOY) 59.04p -2.20%Resolution Ltd. (RSL) 273.40p -2.18%FTSE 250 - RisersAlent (ALNT) 358.00p +0.82%COLT Group SA (COLT) 102.50p +0.49%PZ Cussons (PZC) 366.80p +0.38%NMC Health (NMC) 312.00p +0.29%Pennon Group (PNN) 662.00p +0.23%UK Commercial Property Trust (UKCM) 74.00p +0.07%Menzies(John) (MNZS) 696.00p 0.00%BH Global Ltd. USD Shares (BHGU) 11.4 0.00%Bumi (BUMI) 259.30p 0.00%Renishaw (RSW) 1,702.00p 0.00%FTSE 250 - FallersUnite Group (UTG) 326.20p -6.13%Home Retail Group (HOME) 135.70p -5.83%Computacenter (CCC) 446.60p -4.55%Genesis Emerging Markets Fund Ltd. (GSS) 495.60p -4.51%Man Group (EMG) 84.35p -4.09%JPMorgan Indian Inv Trust (JII) 339.90p -3.49%Barratt Developments (BDEV) 295.50p -3.40%Ferrexpo (FXPO) 140.00p -3.31%Morgan Advance Materials (MGAM) 262.10p -3.21%Imagination Technologies Group (IMG) 286.40p -3.15%