Learn German: Ist die Erde am ältesten? - Is the Earth the oldest?

In German, when a superlative describes how something is (like here, 'the Earth is the oldest') rather than being placed right in front of a noun (like 'the oldest planet'), it requires the word am and the ending -sten. This is called the predicate form.

Why does ältesten have an umlaut (ä) when the basic word for 'old' is alt?

Many short, common adjectives with the vowels a, o, or u get an umlaut in their comparative and superlative forms. So, alt (old) changes to älter (older) and am ältesten (the oldest).

Why is there an extra e before the -sten ending in am ältesten?

If an adjective ends in certain consonant sounds like -t, -d, -s, or -z, German adds an extra e before the -sten ending to make it easier to pronounce. Because alt ends in a t, we say am ältesten instead of am ältsten.

Does die Erde mean the planet Earth or dirt/soil?