Learn Finnish: Uskooko kukaan, että ennätysmäinen maanvyörymä on mahdollinen? - Does anyone believe that a record-breaking landslide is possible?

This ties into exactly what you are learning! In direct questions like this one, as well as in conditional clauses and comparisons, negative pronouns like kukaan (usually 'no one') are used to mean 'anyone' at all. If you used joku instead, the question would specifically mean 'Does someone believe...?' rather than 'Does anyone...?'

How does the suffix in ennätysmäinen work?

The word is formed from the noun ennätys (a record, like a world or historical record) and the adjective-forming suffix -mäinen. This suffix means '-like' or '-esque'. So ennätysmäinen literally means 'record-like', which translates smoothly to 'record-breaking' in this context.

What are the root words that make up maanvyörymä?

It is a compound of maan (the genitive form of maa, meaning earth, land, or ground) and vyörymä (a slide or avalanche). The word vyörymä itself comes from the verb vyöryä, which means to roll, surge, or avalanche.

The verb uskoa (to believe) often requires the partitive case. Why isn't there a partitive word here?

You are right that when you believe a person or a thing, that object is usually in the partitive (for example, Uskotko minua? - Do you believe me?). However, in this sentence, uskooko is followed by an että (that) clause rather than a direct object noun. The whole subordinate clause acts as the thing being believed, so no partitive noun is needed here.