Quite Plausible...read on....
well, hinduism is a pagan religion. there is no concept of God in Hinduism but several gods representing different forces of nature, indra, varun, etc. the purans and upnishads were written in medevial time by corrupt brahmins to fulfil their own interests. they all are well contradicting. shiva mahapuran states that in the beginning there was shiva, and he created brahma and vishnu, while vishnu puran states the same for vishnu.
as for shivling, one puran states that it's a representation of virility, ling means male genitals. scriptures say that once shiva was making love with parvati and agatsya muni knocked the foor. shiva couldn't open the door and was cirsed by agatya that he'll he'll be worshipped in the same form (ling over yoni, the common depiction of shivling).
another legend states that some sages who were jealous of shiva's masculinity cut his genitals, which fell through all the worlds(loks) creating tremors. parvati was requested to stop the ling, so she stopped it on her yoni. so you can see how much the purans differ.
as for the pagan hindu gods, they are considered to be the souce of/or eveloved from the same source as greek and roman pagan gods (like zeus:indra, uranus:varun, jupiter:brihaspati/guru).
some even say that abraham and sara are obscure forms of brahma and sarasvati, but this is debatable.
the legend of noah or nooh is stated in vedas as the legend of manu. manu saved the mankind from the flood, so the sanskrit word for man is "manav", son of manu. and it's so similar to the word "man".
i can go on forever but in a nutshell, humanity evolved at a single place and migrated, and carried along with it the legends. which changed significantly as generations passed. and also due to the later inter mixings and migrations.
-anonymous