Earth: Inside and Out: Course Preview

Banded Iron Formation

This video was developed for Week 3 of the AMNH online course Earth: Inside and Out, part of Seminars on Science, a program of online graduate-level professional development courses for K-12 educators. Explore more sample resources...


Authoring scientist Dr. Ed Mathez shows how the presence of banded iron layers in the bedrock of the oceans proves that at once point in time there must have been a good deal of iron dissolved in Earth's oceans. The iron began reacting with the oxygen released by organisms engaged in photosynthesis, forming crystals of iron oxide that became the reddish layers of banded iron seen in the rock in this video.