On rocks, from Mineral Cup’s admin, @mikamckinnon
She writes:
#Hematite is a key mineral in banded iron formations. And BIFs are my BFFs

Very well done! BIFs make their appearance around minute five.

https://www.ted.com/talks/mika_mckinnon_do_you_have_a_rock

Thanks for the heads up
@vickyveritas
@vickyveritas.bsky.social

#MinCup25 #BandedIronFormation #GreatOxidationEvent #Stromatolites #EarthHistory #EarthSystemScience

Banded Iron Formation

This beautiful rock from Australia is one of a type called Banded Iron Formation (BIF) found all over the world. BIF are very cool because they tell us about the evolution of the early atmosphere and that free oxygen was not widespread in the early Earth.

The oldest BIF appear in the rock record 3.8 billion years ago and the youngest appear 1.8/1.7 billion years ago. These rocks represent deposits of iron oxides that precipitate from iron in seawater as the result of oxygen production.

The fact that the early oceans contained iron means that they could not have contained much oxygen and, in the pre-BIF earth, free oxygen was likely rare or absent. The formation of BIF stopped once the majority of iron from the oceans was used up allowing the oxygen, created by early organisms engaged in photosynthesis, to build up in the atmosphere.

Banded iron formations appear to have been deposited in areas of the ocean where seawater with high contents of dissolved iron and silica came into contact with water containing higher amounts of oxygen, which resulted in the precipitation of hematite and chert (microcrystalline silica).

This rock is from the Karijini Gorge in Western Australia. This unique formation is the largest iron deposit on Earth and records evidence of what early oceans were like.

See also: https://en.m.wikipedia.org/wiki/Banded_iron_formation

Image from: http://www.globalstone.de/picas/australia/0101.jpg

#BandedIronFormation #BIF #geology #ScienceMastodon