Intruder' stars have changed Earth's climate over the eons. Here's how.

The thing that interests me most about this story is the passage of HD 7977 about 2.8 million years ago. That is almost exactly when the most recent series of ice ages is believed to have started. Previously, theories for the start of this series of ice ages focused on the rise of the Central American mountains cutting off sea level flow of water between the Atlantic and Pacific, plus rapid weathering of rocks exposed by the tectonic uplifting there and concurrently elsewhere, such as the Himalayas, which is believed to have substantially lowered atmospheric CO2 levels.

But, if this passing star changed Earth's orbital parameters, that could be a big factor in this substantial climate change, too.

Looking at the geology and the astronomical information together might give a better picture of both how the climate changed and how close the star probably came to us.

On another note, I am wondering what the night sky looked like 2.8 million years ago when this star was at its closest approach. For that matter, would it have been visible during the day, too?

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