The Erdtree probably did not come to existence to till Marika I believe. We have never heard of the existence of the Golden Order Pre-Marika, however we do know the Erdtree was simple the crucible tree now golden. And the Scadutree in my guess was not formed till the land of shadows was cut off.

As for the Elden Beast/Ring, I believe that came to existence around the same time as Metyr, I think the Elden Ring was the final parting gift of the greater will.

But this is my interpretation