NPR News

First Aid Kit is two young Swedish sisters — that's Klara Soderberg on the left and Johanna Soderberg on the right — who make utterly charming, folk-infused pop music that lulls and enchants, with an obvious nod to late-'60s and early-'70s bands like Crosby, Stills & Nash. Their voices intertwine in that way sibling singers' sometimes do, with disarmingly lovely results, but the music remains distinctly alluring and adventurous.

Imagine your kitchen, if you have one. What's in it? Appliances? Food on the counters? Is it messy or sparse? Fully stocked or running on empty?

The late astronomer Carl Sagan presented this paradox to his colleagues: We know the sun was a lot fainter two billion years ago. So why wasn't the Earth frozen solid?

We know it wasn't because there's plenty of evidence for warm seas and flowing water way back then. The question is still puzzling scientists.

But new clues to that paradox come from an unlikely source: fossilized raindrops, from 2.7 billion years ago. Back then, the Earth had no trees or flowers or animals birds or fish. But it did have volcanoes. And it did rain.