Many frogs and other amphibians are disappearing, and scientists don't know why. Fish populations across the world are on the verge of collapse. We used to feed on top carnivores, like tuna - great big fish that are easy to catch and feed a lot of people. You can still catch those fish, but there aren't as many. The average fish we're catching now is lower in the food chain - it's smaller and feeds closer to algae.
Scientists say species are always going extinct, but usually at a much slower pace.
Large extinctions occur only every 20 million to 25 million years. Then the number of species gradually builds back up. That's what everyone is worried about. Most scientists would suggest it will be greater than what occurred during the dinosaur die-off about 70 million years ago. No one knows for sure why the dinos disappeared, but humans didn't have anything to do with it - they didn't exist.