It's impossible to say with absolute certainty what the very first solids that formed on Earth were, as those early conditions are incredibly difficult to recreate and study. However, based on our understanding of Earth's early history and the chemistry of the solar system, it's likely that the first solids were minerals formed from the cooling and condensation of the initial planetary disk.

Here's a breakdown of the likely candidates:

* Calcium-Aluminum-Rich Inclusions (CAIs): These are some of the oldest materials found in meteorites, and they are thought to have formed in the very early solar system. They contain minerals like perovskite, anorthite, and spinel, which could have been among the first solids to form on Earth.

* Olivine and Pyroxene: These are common minerals found in the Earth's mantle, and they are known to form at high temperatures. They could have been among the first minerals to crystallize from the molten Earth.

* Iron-Nickel Alloys: These metals are also common in meteorites and are thought to have been present in the early Earth. As the Earth cooled, these metals would have started to solidify.

It's important to note that these are just hypotheses based on our current understanding. The exact composition and formation of the first Earth solids are still subject to debate and ongoing research.