2015: The year in pictures

We ended 2015 the way we started, confronting terrorism both abroad and in the U.S. The Charlie Hebdo attack in early January in Paris shocked the world with its brazenness. The Paris and San Bernardino attacks at the end of the year dramatically increased our awareness of a global threat as the world confronted an increased sense of insecurity in our daily lives.

In between, we made history with the restoration of diplomatic relations between the U.S. and Cuba, the legalization of same-sex marriage nationwide and a landmark climate change agreement. We celebrated Team USA's third World Cup title, saw American Pharoah become a Triple Crown winner and applauded Serena Williams as Sportsperson of the Year. Deflate-gate took away some of the luster from Tom Brady and the Patriots.

The Black Lives Matter movement continued to spark debate about police violence against blacks and race in America.

We were confronted with dramatic, harrowing images of Europe's worst refugee crisis since WW II, bringing home the scale of the humanitarian crisis and the risks taken by hundreds of thousands to reach a better life.

Donald Trump's serious challenge for the Republican nomination surprised many, creating a tumultuous campaign with too many crazy moments to recount. We can only assume there are more to witness in 2016.

Science continued to awe us with amazing photos of Pluto and Mars. A child received the first double hand transplant. Cecil the Lion's poaching became a rallying cry for animal rights activists.

The "rock star" Pope Francis kept rocking the world as he toured Latin America, Cuba, Africa and the U.S.

All of these events and more were captured in photographs, leaving an indelible impression and helping us understand events both monumental and seemingly ordinary this past year.

Radhika Chalasani is senior photo editor at CBSNews.com - On Twitter