Pangaea and the arrival of the Oceans
I would suggest here that the Mars size projectile would be covered by at least 50 km thick of ice in order to give us our oceans.
It would beggar belief that the oceans could arrive piecemeal onto a recent molten orb that even 250 million years ago was in support of a molten supercontinent.
However clearly it would take many millions of years to oxygenate those oceans.
I would further suggest the Mars size projectile was not a glancing blow but would burrow its way into the centre of planet Earth shedding its cargo of ice transforming the surface of planet Earth and leaving us with a safety valve for the molten material within which was to become our ancestral home Pangaea.
However the Mars size projectile would blast a large amount of molten material out into space in order to form our Moon.
We now consider what is called "the effects of gravity" Every particle in the Universe attracts every other with a force which is proportional to the product of their masses and inversely proportional to the square of their separation