Yesterday, I came across this cool little representation of mid-ocean spreading centers. I really like this because so far as I can remember, paleomagnetism and it’s role in the establishment of continent drift as legitimate was kind of the first time everything “clicked” for me in regards to geology.
Before the discovery of plate tectonics, geologists assumed that the continents are where they are and always have been. They never suspected that they might be moving bodies. Alfred Wegener tried to change that thinking and was met with a great deal of opposition. He was German and the German’s were not well liked at the time (1920’s). He provided evidence of continental drift but had no idea how it could be occurring.
As igneous rocks like basalt cool, they have tiny magnetite crystals forming inside of them that act like a compass. As the heat energy within the melt lessens and the rock is actually formed, these magnetite crystals align themselves to the current polar north.
When scientists first developed instruments that could detect the magnetic field put off by rocks they were quite surprised to find that the magnetic orientation of many rocks did not match the orientation of today’s magnetic pole. That meant that either the rocks had moved, or the magnetic poles had. Initially, they assumed that it was the latter. However, when rocks of similar ages were tested from different continents, their magnetic orientations didn’t match. That means that relative to each continent, the magnetic pole would’ve had to been different; which isn’t possible. With that line of logic you’re left with the idea that the continents had moved as well as the magnetic poles moving! Wegener redeemed.
As time moves forward, technology advances and with the help of WWII, the geography of the ocean floor begins to surface (Not literally. Well, in some places literally). The discovery of mid-ocean ridges, trenches, sea mounts and fracture zones providing more tantalizing evidence for the theory that Wegener put forth years prior. Wegener suggested the idea of sea-floor spreading when he first proposed his ideas about continental drift, but had no evidence or way to test this hypothesis.
So how do you test it?
Aside from waiting and measuring if the continents were getting further apart, with our knowledge of paleomagnetism, one could simply measure the paleomagnetism of the rocks surrounding a mid-ocean ridge. You only have to look up at the above image to understand why this works: As the polar north wanders and reverses, that information would be preserved in the rocks around the mid-ocean ridge. If the sea floor is spreading, each side of the mid-ocean ridge, ideally, should be a mirror image of its opposite. If spreading is occurring, rocks are forming at the same time and being forced apart in opposite directions.
So when researchers headed out to get this data, and found this…
I can only imagine they were really excited. If you note that the mid-ocean ridges exists along all of the dark red portions of the map, and that each color radiating out from the red represents a polar reversal– you have direct evidence of sea-floor spreading and continental drift.
The way all these seemingly disparate elements come together to prove what is a foundation to a theory that would go on to be one of the greatest paradigm shifts in the history of science amazed me. It’s so tangible and easy to understand. Maybe I love it so much because it’s so easy to visualize. As an artist, I was obsessed with symmetry and motif, and this is the prime example of the organized chaos of nature: the repeating symmetry in the world that drives the random nature of what we see around us.
I’m sorry if this is really rambling and incoherent. I hope it makes sense. I don’t have an editor and this blog is stream of consciousness kind of thing. I apologize for typos and grammatical terrorism, I only give it a quick once over before hitting the submit button.