Joining the lights-out list was the Opera House in Sydney, Australia, where Earth Hour originated in 2007, as a small movement with a working title of "The Big Flick." San Francisco joined Sydney in that first year; the very next year, people in 35 countries got onboard. The number of people and countries participating has increased every year, even as the date for the annual event has changed. It is always the last Saturday in March.

Among the iconic world landmarks gone dark were these:

• the Empire State Building, in New York City
• Big Ben, in London
• the Great Pyramids, in Giza, Egypt
• the Christ the Redeemer statue, outside Rio de Janeiro, Brazil
• the Sydney Opera House, in Sydney, Australia
• the Eiffel Tower, in Paris
• the Acropolis, in Athens, Greece
• the Colosseum and St. Peter's Basilica, in Rome
• the Alhambra palace in Granada, Spain
• Taipei 101, in the Taiwanese capital
• the Burj Khalifa, the world's tallest building, in Dubai.