Why are weeks 7 days?

Why are weeks 7 days? Why do we have five weekdays and then two days for the weekend? 

I understand there is a religious backstory...but are there any other causes for this structure? 

It was associated with the seven heavenly bodies; the Sun, Moon, Mars, Mercury, Jupiter, Venus and Saturn. For this reason, some believe, marking rituals every seventh-day became important. A seven-day week based on these same celestial bodies was adopted as far away as Japan and ancient China. 

It seems like a stupid but actually quite important question. Who is to say that we would not all be happier and more efficient people if we worked 3 days, took a one day break, and then worked another 3 days. 

Or what if weeks were 30 days long? 

Or 4 days long?

Like why 7? 

Are companies more productive (output) when their employees work like this? Who makes more money because of this structure?

I feel like we are missing some sort of necessary logical explanation here. 

If not, has anyone ever experimented on this? Would it make a difference? 

Curious your thoughts. 

1 response
I think a "day" should be 36 hours long. 12 hours to work 12 hours to sleep and 12 hours yo do whatever. Work weeks should be 3 12 days a week only. Just my thoughts.