Ereshkigal in Proto-Indo-European myth...

When trying to validate the concept that 'our' myths have their origin in the Rig Veda, or rather, when trying to follow the paths the story-lines share, I keep on finding that what I have taken as pretty solid evidence keeps on crumbling away.

In the oldest of the Persephone stories, the dragon, the stranger, the mountains, the river took the sister of the Queen of Heaven.

And gave to her the Underworld.

No one could get her back...This story- from the tablet known as: Gilgamesh, Enkidu, and the Netherworld was probably composed during the Ur III period 2100-2000 BCE.

Is that older or younger than the Rig Veda?

It isn't hard to believe that a concern with water- too much or too little, with cattle and with women is pretty universal when farming begins. So, let's call that layer, Neolithic.

What lies deeper within?

The enveloping force personified as a serpent, is the enemy.
The weapon of choice is the thunder-bolt:
And the sacred drink: soma.

He slew the Dragon lying on the mountain: his heavenly bolt of thunder Tvaṣṭar fashioned.
Like lowing cattle in rapid flow descending the waters glided downward to the ocean.

Impetuous as a bull, he chose the Soma and in three sacred beakers drank the juices.
Maghavan grasped the thunder for his weapon, and smote to death this firstborn of the dragons.

When, Indra, thou hadst slain the dragon's firstborn, and overcome the charms of the enchanters,

Then, giving life to Sun and Dawn and Heaven, thou foundest not one foe to stand against thee.

Brewing developed with farming, but psychoactive plants just grow....As has been noted elsewhere, the Rig Veda often describes the effect of Soma and soma itself as fluid as rain, as brilliant as the lightning flash and radiant, like the sun:

He has clothed himself with the fire-burst of the sun..
Soma shines together with the sun...

Hasan Javaid Khan names the plant as ephedra.

When people first crawled inside mountains and discovered absolute and total blackness, they knew it to be sacred. The space of limitless potential. They drew animals because they saw animals in the rock illuminated by flame...the animals they had killed, and the animals that would flow like water through the land.

At that time the mountains were full of the power of the Underworld and that power was represented by the omega symbol of the womb.

Ereshkigal- Queen of the Great Earth was mother of wild things, Lady of the Stony Ground, her children are killed by hunters and harmed by captivity. Should any domesticated animal stray into her wasteland, it will die.

By the Neolithic period, the earth was the zone of regeneration, as the 56 Aubrey holes were dug at Stonehenge to receive cremated remains. The land was Aruru- birth giver.The origins of the solar symbols, the cross and the circle, were probably obscure even then, belonging to the time before farming. Likewise the internal structures of megaliths and perhaps even the carvings on the stones at Bryn Celli Dhu and Newgrange belonged to the time before farming. Many of the carved stones of Newgrange had been placed carved side backwards, as if they had been taken from another, perhaps older, structure and the carvings were incidental...

But the power lingers, and old pattens are repeated and preserved in Stonehenge and at The Sanctuary.

By 2200 BC in Britain, the importance of the sun as agent of growth made the glitter of gold and copper and the solar cross, extra significant. The winter sun is the male sun who takes longer and longer journeys travelling through the ground,seeking regeneration.

Nevertheless, the Underworld has a solar connection, and Ereshkigal was sister to the sun.

The Hittites had a sun goddess called Arinna who had a male reflection,  the "sun god in the water" His name was Ishtanu (Ištanu; from Hattic Estan, "Sun-god"). In Luwian he was known as Tiwaz or Tijaz depicted bearing a winged sun on his crown or head-dress, and carrying a crooked staff.

Hymn to Istanu (Hittite), CTH 372.1.39-46:
When in the morning Istanu rises in the sky, then on the upper lands and lower lands, all of them, comes your illumination, Istanu. You are the one that judges the case of the dog and the pig; the animals’ case, that do not speak with the mouth, you judge; the evil and wicked man’s case you, Istanu, do judge.

The Akkadian version of The Descent of Inana preserves the idea of the sun changing sex in the story of Dumuzi spending half the year in the Underworld until his sister returns to swap places with him.

The mother who gave birth, Ereshkigal,
lay there sick (with grief) for her children,
her pure limbs no linen veiled
her bosom had nothing drawn over it
her nails were like a copper rake upon her,
the hair on her head was like leaks....

And Ereshkigal becomes mother of demons.

The shivers and chills of death
that fritter the sum of things
spawn of the god of heaven
spawned on an evil spirit
the death warrants, beloved sons of the storm god
born of the queen of the Netherworld
who were torn out of heaven and hurled from the earth as castoffs
are creatures of hell, all.

Up above they roar, down below they cheep
they are the bitter venom of the gods
they are the great storms let loose from heaven
they are the owl (of ill omen) that hoots in the town
spawn spawned by the god of heaven, sons born by earth are they.
Over high roofs, over broad roofs like a floodwave
they surge
from house to house they climb over.

Doors do not hold them, locks do not restrain them,
through the doors they glide like snakes
through the hinge boxes they blow like wind.
From a man's embrace they lead off the wife
from the man's knee they make the child get up
and the youth they fetch out of the house of his in-laws
they are the numbness of the daze
that tread on the heels of man.

The Queen who loves battle-axes (from 'The Death of Ur-Nammu) .

Why did the Mesopotamian  Bronze Age story require Ereshkigal to be 'taken by the Kur'?

Because the story was written during the time of Sumerian renaissance, when the Akkadians were trying to restore their Sumerian identity after the Gutians (possibly from Kurdistan, beyond the Zagros mountains) had been expelled, and whilst the horror of abduction and murder by the foreigners from the mountain was still raw?

A poem recorded and un-dated by Thorkild Jacobson in The Treasures of Darkness page 77

Alas! that day of mine, on which I was destroyed;
alas! that day of mine, on which I was destroyed
.................................................................................

For on it he came hither to me in my house,
for on it he turned in the mountains
into the road
into me.

For on it the boat came on my river towards me,
the boat moored at my quay,
for on it the master of the boat came in to me,
for on it he reached out his dirty hands towards me,
for on it he yelled to me:"Get up! Get on board!"
for on it the goods were taken aboard in the bow,
for on it I, the queen, was taken on board in the stern.
For on it I grew cold with shivering fear.

The foe trampled with his booted feet into my chamber!
He reached out his dirty hands towards me!
He reached out the hand towards me, he terrified me!
That foe reached out his hand towards me,
made me die with fear.

That foe intimidated me- I did not intimidate him.
That foe stripped me of my robe,
clothed his wife in it,
that foe cut my string of gems,
hung it on his child
I was to tread the floors of his home...