Can Atheism ground objective morality?

[The Tanager]

In my exploration and discussions, I have not seen an atheistic worldview be able to logically account for morality being objective. The closest I've seen is an atheistic platonic kind of moral system, but while that seems to be able to account for the existence of 'good' and 'evil', it still doesn't seem to account for why humans would be obligated to choose Good over Evil. I'd love to hear cases from those who think atheism can account for objective morality to make sure I haven't missed (or misunderstood) thoughts in my exploration.

[Bradskii]

I think you are still misunderstanding what is going on here. (a) is a definition and (b) involves what would follow from that definition, if theism were true. It doesn’t matter what the fact of the shape of the earth really is, whether theism or atheism is true, or anything like that.

Subjective means something which I prefer. You could say that if I'm going to design a simple shape from wood I might prefer it to be round. But when I've made it, the fact that I preferred what shape it was going to be doesn't make the shape subjective. It's an objective fact that it is round.

The fact that God decided the planet was going to be round doesn't make the shape subjective. If that was the case, then nothing is an objective fact. It wouldn't be an objective fact that we circle the sun, because God preferred that. It wouldn't be an objective fact we're an evolved species because God preferred that.