10 Questions That Science Can't Answer Yet

How Many Species Are on Earth?
By some estimates we’ve still only accounted for 1.5 million species, or around 15 percent of the total number on Earth. Danita Delimont/Getty Images

Earth is home to a dazzling array of creatures and plants. Pink flamingos fill the skies, humongous elephants stomp through the savannas, and weird fruits and ferns hide in crevasses everywhere. We'll never know how many different species roam our planet. There are just too many. But that doesn't stop scientists from trying to determine that elusive number.

Botanist Carl Linnaeus realized two and half centuries ago that humans needed a system for keeping track of our planet's species. He began classifying both plants and animals using taxonomic language that named, ranked and classified creatures and plants.

After generations of work, by some estimates we've still only accounted for 1.5 million species, or around 15 percent of the total number. That means the majority of organisms still need adequate description. That's especially true for undervalued and underappreciated species such as fungi, of which we've really only described maybe 10 percent. In contrast, we've done a pretty good job with our fellow mammals, most of which are already logged.

All of the numbers are simply statistical guesses, so we may never really know if they're accurate. Perhaps the bigger concern is that species seem to be disappearing a rate faster than at any time since dinosaurs vanished 65 million years ago. After all, if creatures are disappearing en masse, we humans could be next.