TIMELINE: BHP Billiton's year-long pursuit

(Reuters) - The world's top miner BHP Billiton said on Tuesday that it is dropping its proposed $66 billion hostile takeover of rival Rio Tinto, citing worsening market conditions and European regulator's demands it sell prized iron ore and coal assets.

Following is a chronology of the long-talked-of bid, which would have created the world's biggest mining force.

* November 8, 2007 - BHP, the world's biggest mining group, proposes to buy Rio through a three-for-one share swap. Rio shares soar as much as 30 percent. Rio rejects the proposal as vastly undervaluing the firm and its prospects.

* November 12 - BHP says takeover plan would result in $3.7 billion in synergies in seven years. It promises to hand $30 billion to shareholders via a share buyback if deal goes through. Rio says the bid remains "well out of the ballpark."

* November 14 - Aluminum Corp of China Ltd. (Chalco) says it is worried about BHP's bid.

* November 20 - China's steel industry, the world's largest, is deeply concerned about proposed BHP-Rio merger, a Chinese state newspaper reports. Eurofer, the lobby group for the European steel industry, says it will ask European Commission to block it.

* November 26 - Rio says it does not need BHP's offer, unveiling plans to double iron ore output by 2018, raise its dividend and generate at least $15 billion in asset sales.

* November 27 - Seven banks pledge to raise $70 billion of financing for BHP's planned bid.

* December 4 - A Chinese newspaper says China's top steelmaker, Baosteel, may bid for Rio, but later the firm denies the report.

* December 7 - Rio says it has had offers from other suitors, but has not engaged with them and is sticking with its independent growth strategy.

* December 11 - Rio asks Britain's Takeover Panel to set a deadline under its "put up or shut up" rule, under which BHP has to formalize its bid or walk away.

* December 21 - Britain's Takeover Panel imposes February 6 deadline for BHP to make a formal bid, or abandon bid for six months.

* January 25, 2008 - Rio CEO reiterates BHP bid is too low, saying it was "two ballparks away" from fair value.

* February 1 - Aluminum Corp of China (Chinalco) and Alcoa say they bought a 9 percent stake in Rio worth $14 billion. They say they do not currently intend to make an offer for Rio, but reserve the right to do so in the future.

* February 6 - Rio Tinto rejects sweetened BHP $147.4 billion takeover bid.

* April 14 - Rio defends its rebuff of unwanted suitor BHP, saying it is better off riding China's commodities boom alone.