I think it's because the context going by the title is earth based for me. Whenever I've heard mention of tectonics it's related to earth and and the only mercu

I think it's because the context going by the title is earth based for me. Whenever I've heard mention of tectonics it's related to earth and and the only mercury on earth is the element, so my brain zoomed in on that. I remember once asking a german friend if she didn't think that english was better for only having one form of my, the, etc. She said that in german there was less room for confusion because the listener would immediately know whether 'my friend', for example, was a boy or a girl. German is more strongly typed, we rely more on the context in english. It seems that in my experiences Mercury the planet and Mercury the element have never before come up in a context where there could be ambiguity.