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Banded iron rocks, formed before oxygen saturated the atmosphere but after photosynthetic bacteria started releasing oxygen into the ocean, alternate layers of different iron-containing minerals that may reflect changes in bacterial population.
#geology #prehistory
https://www.atlasobscura.com/places/banded-iron-formation-stone
“The Mystery of Florida’s Cannonball-Eating Spanish Fort”
The rock it’s made from, coquina, is a sedimentary rock made up of compressed seashells. It turns out that under impact, the component shell fragments can shift, absorbing the impact. This explains why cannonballs simply sank into the walls like pressing into foam instead of shattering them.
https://www.atlasobscura.com/articles/coquina-fort-in-florida
Interesting #geology read: There’s a break in the rock layers in many places worldwide, ending 700 million years ago. One hypothesis: an ice age with enough glacial activity to scour the crust worldwide. As it turns out, they’ve found signs of a massive surge in rocks being recycled through volcanoes around that time…
https://www.latimes.com/science/sciencenow/la-sci-sn-snowball-earth-geology-20190103-story.html