Would the earth have soap if plants did not exist?

No, the earth would not have soap if plants did not exist. I believe this because soap plants (of the genus Chlorogalum) are essential to our making of soap. We use these plants to make all kinds of soap, by using the sap of these plants. However because this does not complete the question, I will explain further. Plants are the only way that the compound 'saponin' exists. Saponin forms the bubbly lather.