Sounds like a stupidly easy question to find out with a quick internet search, but it’s not.
I don’t want to know the average surface temperature, or the average ocean surface water temperature, or read another article about climate change.
But that’s all I found in the past hour.
I’d like to know the average temperature of all molecules that comprise earth, or a best guess scientific estimate.
I don’t think that’s an answer that really exists in any meaningful sense since temperature is a macroscopic phenomenon. When you get down to the scale of the microscopic, i.e. of molecules, then atoms, then particles, you really only have amounts of kinetic energy of said particles, typically measured in the unit electronvolt, or eV.
When said particles interact, they impart kinetic energy to one another, which directly constitutes the thermodynamic fluctuations we see in macroscopic systems.
Put simply, microscopic energy levels create macroscopic temperature readings.
In other words, “temperature” is just a macroscopic reading of collective microscopic energy levels.
tl;dr: Molecules don’t have temperature; they have energy.
You need this distinction when it’s about gas.
Here we are talking solid and fluid matter.