It's impossible to say exactly how many different types of organisms scientists have discovered so far. There are a few reasons for this:

* Ongoing Discovery: New species are being discovered all the time, especially in remote areas and in microscopic life forms.

* Difficult Classification: Defining a "species" is complex and can be debated. The criteria used for classification vary between groups of organisms.

* Uncounted Microorganisms: The vast majority of microorganisms, like bacteria and fungi, haven't even been identified yet. Some scientists estimate we've only identified 1% of all microorganisms.

However, here are some estimates:

* Named Species: There are approximately 1.8 million named species of plants, animals, fungi, and microorganisms.

* Estimated Total: Some scientists believe there could be anywhere from 5 to 100 million species on Earth, with many estimates falling between 8 and 10 million.

The Bottom Line: We know a lot, but we're still discovering and learning about a tremendous amount of biodiversity on Earth.