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Electromagnetic Link Deep in the Earth Varies the Length of the Day

Scientists find that 2600 kilometers down, the Earth is electrically conductive. The mineral responsible could point the way to new superconductors

3 min read

4 April 2008—You probably haven’t noticed, but the length of a day is not what it used to be. Though only on the order of a few milliseconds’ difference and observable only over a period of decades, the time it takes the Earth to make one revolution varies. This anomaly has teased earth scientists for some time. They suspected that it is due to the exchange in angular momentum between the Earth’s fluid core and rocky mantle, but how that happens was still a question.

In today’s issue of Science , researchers at the Tokyo Institute of Technology provide evidence that a mineral phase in the Earth’s mantle is electrically conductive and could be doing the job by electromagnetically linking the core to the mantle. The Tokyo scientists say that the conductive mineral could point superconductor researchers in a new direction, too.

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The Transistor at 75

The past, present, and future of the modern world’s most important invention

2 min read
A photo of a birthday cake with 75 written on it.
Lisa Sheehan

Seventy-five years is a long time. It’s so long that most of us don’t remember a time before the transistor, and long enough for many engineers to have devoted entire careers to its use and development. In honor of this most important of technological achievements, this issue’s package of articles explores the transistor’s historical journey and potential future.

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