When did the first frog appear on earth?

The correct answer will be around 250 million years ago.

Explanation:

Frogs are the cold-blooded animals which lives in both water and land. So, they belong to the class amphibia.

The first amphibians appeared during Devonian period around 370 million years ago when life moved on land from water but the evolution of frogs is a debated topic.

Fossil evidences have shown that they evolved around 250 million years ago during the early Triassic period from Triadobatrachus, or triple frog. The earliest known true frog was tiny Vieraella species found in the South America.

Thus, frogs appeared for the first time around 250 million years ago.