What evidence suggests Earth is entering a sixth mass extinction?

Although it may not be obvious, another devastating mass extinction event is taking place today the sixth of its kind in Earth's history. The trend is hitting global fauna on multiple fronts, as hotter oceans, deforestation, and climate change drive animal populations to drop in unprecedented numbers. These alarming extinction trends are driven by one key factor: humans. According to a 2014 study, current extinction rates are 1,000 times higher than they would be if humans weren't around. A summary of a United Nations report released last month put it another way: "Human actions threaten more species with global extinction now than ever before," the authors wrote.