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.

explanation:

b,bacteria convert nitrates

into nitrogen gas.

d,plants and animals take in

and use nitrogen compounds.

e,bacteria break down waste    

products and return nitrogen  

to the soil.

a,bacteria convert atmospheric

nitrogen to ammonia.

c,bacteria convert ammonia

to nitrites and nitrates.

this age may represent the age of the earth's accretion, of core formation, or of the material from which the earth formed. this dating is based on evidence from radiometric age-dating of meteorite material and is consistent with the radiometric ages of the oldest-known terrestrial and lunar samples.