I want ask how to know the age of earth with superparamagnetism ( magnetic rock) ?
I think you will need to elaborate. i think what you might be confused with is oceanic spreading rates (the rate at which the spreading ridges form new oceanic crust). As these rocks cool down below the curie temperature, Earth's magnetic field will have an affect on mineral alignment, recording which way Earth's magnetic field was at the time the rock cooled.
As an aside, Earth's magnetic field is caused from the rotation of the hot metallic solid core; Earth has not always had this.
Thanks for your reply
I hope I get more information about this topic
The Earth's core has always been rotating to a degree, but the magnetic field it generates is not stable. That is why it has reversed thousands of times over the history of the Earth. When an igneous rock cools it will lock in the existing magnetic field when it cools down below roughly 1,200 F. One of the main sources of evidence for plate tectonics was the record of magnetic reversals shown by ships dragging magnetometers behind them on cross Atlantic and other ocean cruises. Especially across the Atlantic you could see a mirror effect depending on how far you were away from the mid Atlantic ridge.
Thanks Mr.Subductonzon for your reply
The age of the Earth is known from radiometric dating. We cannot determine the age of the earth from magnetic studies of rocks.
Yes and no. Magnetic studies certainly can yield a lower bound on the Earth's age.
Well no, really. You cannot independently determine the age of a rock based on magnetic data. In the study you referred they measured the magnetic signature on a rock that they already knew was more than 3 billion years old -- which they then inferred the presence of a geomagnetic field at the time of the rock's formation.
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Thanks for your participate
Exactly. It may also be mentioned that the paleo magnetic orientation of the Earth magnetic field is fixated in the volcanic strata and can be used for a continuous dating scale. See for instance this graph:
Note the white/black bar on top reflecting the paleomagnetic chrons, Matuyama, Gauss, Kaena etc witl alternating normal and reversed orientation of the Earth magnetic field with known reversal dates.
Yes. You can establish a record of how the magnetic field has varied with time once you know the age of the rocks concerned and use them to measure how the magnetic field varies. This effectively gives you a database, which can be correlated with magnetic readings from elsewhere to give you an inference of the age of those rocks. It's important to recognise that the magnetic field is merely a fingerprint (or distinctive pattern) that can give you a "smell" of what the age of the rocks are given prior knowledge -- you absolutely cannot tell the age of the rock given solely magnetic data and no other information.
The magnetic field arises from convection currents in the outer liquid core which constitute a self exciting dynamo.
4.5 bya is what my textbook says
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