Final answer:
The majority of species loss in historical extinctions was due to environmental catastrophes, but the current extinction rate, which mirrors past mass extinctions, is primarily due to human activities such as habitat destruction and climate change.
Step-by-step explanation:
In all of the extinctions that have ever occurred on Earth, the majority of species loss was due to major environmental catastrophes. However, unlike the past mass extinctions caused by events like asteroid impacts or volcanic eruptions, the current period of increased extinction rate, often referred to as the sixth mass extinction, is primarily driven by human activities. These include habitat destruction, introduction of exotic species, over-harvesting, and climate change caused by human-induced increases in greenhouse gas emissions. Historical data show that extinction is a natural evolutionary process, yet the current rates are 500-1000 times the natural background rate, according to biologists. The pace of extinction today is alarmingly rapid, with predictions of species loss within the next century ranging from 10 percent to 50 percent, which has previously only occurred during five other cataclysmic periods in Earth's history.