What is the tallest organism on earth?

Answer 1

It only makes sense to talk about "height" (as opposed to "length") for land organisms supporting their own weight from the base. I could dangle a very long vine from the top of the Empire State Building, but that wouldn't make it "tall", just "long". Similarly, blue whales are very long from head to tail, but they don't stand on their tails (or indeed at all) so we can't really talk about how "tall" they are

The tallest animal (that's not extinct) is the giraffe; male giraffes reach a heights of around 18 feet. Some dinosaurs are estimated to have been as much as 60 feet tall, though this is based on the discovery of only a few fossilized bones and could be considerably off from the true value.

Giraffes are dwarfed in height by even a modestly-sized tree, though, and even the dinosaurs can't compete with the biggest trees. The tallest known living tree is a California redwood (Sequoia sempervirens) which is a little under 380 feet tall.