JUDY WOODRUFF:

And now, a story on this Earth Day that seems lifted from science fiction.

Researchers and entrepreneurs, many in California, are trying to bring back extinct species. Some scientists believe it's a way to correct past mistakes and even help endangered animals.

But just because scientists might be able to do this, are they crossing a line they shouldn't?

Our colleagues at public TV station KQED in San Francisco explored that question in this story produced by Gabriela Quiros and narrated by Thuy Vu.