Authors such as Elizabeth Kolbert were beginning to warn that human activity — greenhouse-gas emissions, urbanization, the global spread of invasive species —were driving Earth toward a “mass extinction” event and something that had occurred only five times since life emerged over 3 billion years ago.
A were driving Earth toward a “mass extinction” event and something that had occurred only five times since life emerged
B were driving Earth toward a “mass extinction” event,
...
A were driving Earth toward a “mass extinction” event and something that had occurred only five times since life emerged
B were driving Earth toward a “mass extinction” event,
...






