Hi -

From their later distirbution around the world, the construction of wooden henge structures was very ancient, with the early stone examples in Africa, Brazil, and Europe.

Stonehenge I was built around 3111 BCE, when fragments of Comet Encke hit the Earth.

From the new radioacarbon dates, Stonehenge II was built in 2360 BCE, when other fragments of Comet Encke hit the Earth. Some hit at Rio Cuarto in today's Argentina, and closer to Europe other fragments impacts likely extincted the people living on Malta.

The global climate consequences were severe globally.

These impacts explain the amount of effort that was spent in building Stonehjenge.

Stonehenge was not an "observatory", but rather a place for celestial ceremonies, likely of "magical" nature, trying to keep the sky in place, so to speak.

I hope this clarifies things for you.

E.P. Grondine
Man and Impact in the Americas