Learn German: Gab es früher Leben auf dem Mond? - Was there life on the moon in the past?

Gab es is the simple past tense of the very common phrase gibt es (is there / are there). It is formed by putting the verb geben into the past tense (gab) and swapping it with es to ask a yes/no question.

früher is the comparative form of früh (early). Why is it translated as 'in the past'?

In German, the comparative word früher (literally 'earlier') is the standard, everyday way to say 'in the past', 'formerly', or to talk about how things 'used to' be.

Since this lesson is about superlatives, what is the superlative form of früh?

The superlative of früh is am frühesten (earliest). Notice the extra -e- before the -sten ending, which is added to make the word easier to pronounce!

Why is it auf dem Mond (dative case) instead of auf den Mond (accusative case)?

auf is a 'two-way' preposition. We use the dative case (dem) when talking about a fixed location—answering 'where?' (Where was the life? On the moon). We would use the accusative case (den) if we were talking about movement towards a destination, like a rocket flying to the moon.