Remember the dinosaurs? They were part of a mass extinction. There's nothing unusual or unnatural about extinction. It's part of life's history. Even mass extinctions have happened before. Today, we are in another period of mass extinction mostly because of human activities.

Scientists have identified around 1.75 million species on Earth, but there are millions still unidentified. Some species might hold the secret to medical cures—but if they disappear, how will we ever know? We're only beginning to understand how complicated all living relationships are!