Introduced in 2009, Bitcoin was the world's first decentralized digital currency. It quickly gained traction amid lingering uncertainty in the wake of financial crisis. Designed to be as rare as gold, Bitcoin was created to have a maximum of 21 million "coins." Initially worth just a fraction of a cent, by February 2011 the currency had gained parity with the US dollar, then it really took off.

The name Satoshi Nakamoto is synonymous with Bitcoin. It is said to be the alias for an unknown IT whizz who invented the cryptocurrency. But despite claiming to be a 30-something Japanese national, it is generally thought that several computer science experts created the technology behind the digital coin. One rumor even suggested that Tesla chief Elon Musk is the real Satoshi, which he denied.

Instead of being printed like dollars and euros, each Bitcoin is created on a global network of computers and verified by the system rather than a bank. There are no transaction fees. The smallest amount you can buy is a "Satoshi" or one-hundred-millionth of a Bitcoin. Purchases can be made anonymously and even at digital currency ATMs. When you buy Bitcoin, it is often stored in a digital wallet.

To ensure that not too much Bitcoin comes into circulation, a process called mining was created where blocks of transactions could only be processed once a difficult math problem was solved by geeks. The puzzles are becoming so complex that bigger and bigger computers are being utilized to decipher them. That's led to concerns about the amount of electricity used to handle Bitcoin transactions.

Due to its anonymous nature, Bitcoin's success is likely being fueled by organized crime, including money laundering and the purchase of illegal goods. The currency is also being targeted by cybercriminals. A recent hack blamed on North Korea forced a South Korean digital currency exchange into bankruptcy. Reports suggest the "Islamic State" armed group used Bitcoin to receive funds to buy arms.

Bitcoin is the largest of all the cryptocurrencies and its incredible rise has spawned many imitators. Other large digital cash creators include Ethereum, Zcash, Bitcoin Cash, Ripple and Litecoin. As of November 2017, their number had swelled to 1,324. Hundreds of others have attempted and failed to launch their own digital coins. The market is now coming under increasing scrutiny by regulators.

2017 was a stratospheric year for Bitcoin. Worth close to $1,000 in January, some twelve months later it had scaled to an all-time high of $19,784. Despite much skepticism, the currency started to see serious interest from institutional investors. Two exchanges began Bitcoin futures trading, allowing speculators to punt on the incredible volatility in the value of the cryptocurrency.

From central banks to respected investors, almost the entire financial establishment warned of a massive Bitcoin bubble, which they said can only end in disaster for holders of the digital currency. Among them was Nobel prize-winning economist Joseph Stiglitz who said Bitcoin "ought to be outlawed." Jamie Dimon, the CEO of JPMorgan Chase labeled those who buy the currency "stupid."

Just before Christmas 2017, Bitcoin saw a dramatic rally, topping out at nearly $20,000 before losing a third of its value in just five days. More intense volatility followed early in the New Year, only to be reversed when it plummeted by almost half. Are we in for an even bigger rollercoaster ride if Wall Street adopts Bitcoin?

Some 2,500 scientists, policymakers and managers came together in Honolulu in June 2016 for the world's largest summit dedicated to the future of coral reefs. With coral reefs threatened by global warming, participants at the 13th International Coral Reef Symposium are calling for a joint rescue effort.

The event gathered guests from 97 countries, including the presidents of Palau, Micronesia, and the Marshall Islands. Coral reefs are a key source of income in those countries, mostly through tourism.

The Pacific nations are worried about the future of their tourist hotspots, as coral reefs face so-called "bleaching" due to rising sea temperatures. "If our coral reefs are further degraded, then our reef-dependent communities will suffer and be displaced," leaders of Palau, Micronesia, and the Marshall Islands said in an open letter.

Bleaching happens when coral is stressed by hot ocean waters or other changes in the environment. In response, corals may release tiny symbiotic algae which drains them of color. More importantly, bleaching affects their ability to feed and reproduce.

Severe or prolonged bleaching might kill off corals entirely. Scientists have detected bleached coral in the past two years in oceans around the world. They expect the process to continue thought 2016.

The 2,300-kilometer-long (1,429-mile-long) Great Barrier Reef is the world's largest coral reef system and its largest living structure. It is also among Australia's main tourist attractions, generating around $3.9 billion (3.5 billion euros) annually.

Almost one-half of the coral in the reef's northern third have died in the past three months [in 2016], according to James Cook University professor Terry Hughes. The most affected area is remote and unpolluted, with very little fishing and no coastal development. "That's an absolute catastrophe," Hughes said. "There's nowhere to hide from climate change."

Despite the bad news, scientists claim the problems can be managed with proper funding and political backing. "We are not ready to write the obituary for coral reefs," Professor Hughes said. The scientific community at the conference pledged to work with leaders across the world in order to "curb the continued loss of coral reefs."