Between them lies the tropical belt, and here - it can be said - is the 'kingdom of Sun'. The ancient Chinese  knew that the width of this belt was slowly decreasing. They had old observatory posts stationed on the tropic of Cancer, and they discovered they had to move them further south as time went on.

North and south of the tropical belt were domains outside the kingdom of Sun. The opposite of the warm and light rays of the sun were, I think, regarded as the cold and dark waves of the sea.

This symmetric model of the globe of the earth was found, however, not to be true. Land was not symmetrically distributed, there was more land in the north than in the south. Water follows the law of gravitation and flows downwards and south should be downwards. Flames, on the other hand, move upwards.

From this experience it was natural to divide the sky similarly, with 'water' in the south and 'dry land' in the north, to create a globe of the sky which reflected the firsthand knowledge of earth.

The Nauru myth of creation (cfr Old Spider and the Clam in the Index) has the salty sea collecting in the lower half of the 'clam':

... One day the Old-Spider found a giant clam, took it up, and tried to find if this object had any opening, but could find none. She tapped on it, and as it sounded hollow, she decided it was empty. 

By repeating a charm, she opened the two shells and slipped inside. She could see nothing, because the sun and the moon did not then exist; and then, she could not stand up because there was not enough room in the shellfish. Constantly hunting about she at last found a snail. To endow it with power she placed it under her arm, lay down and slept for three days. Then she let it free, and still hunting about she found another snail bigger than the first one, and treated it in the same way. Then she said to the first snail: 'Can you open this room a little, so that we can sit down?' The snail said it could, and opened the shell a little. 

Old-Spider then took the snail, placed it in the west of the shell, and made it into the moon. Then there was a little light, which allowed Old-Spider to see a big worm. At her request he opened the shell a little wider, and from the body of the worm flowed a salted sweat which collected in the lower half-shell and became the sea. Then he raised the upper half-shell very high, and it became the sky. Rigi, the worm, exhausted by this great effort, then died. Old-Spider then made the sun from the second snail, and placed it beside the lower half-shell, which became the earth ...

Rigi, the one who died of the effort of raising the upper half-shell very high, I will equate with Kuukuu the planter who died of the effort of lifting the 'turtle'.

The opposite of raising the sky dome high is to helplessly (with arms akimbo) watch it sink down, not only to its original position but down to a lower level. But such is the rule of the world, any action will cause a reaction.

On Easter Island, they must have been aware of their position - outside the tropical belt, and threatened to be washed out into the dark and cold waves of the southern sea. But in cosmic terms (in the language of Manuscript E) it was not down on earth Uoke worked with his pole, it must have been in the sky.

The 'sea' in the sky was in the south, also on Easter Island, and 'land' must have been in the north.