The Jaramillo reversal was a reversal and excursion of the Earth's magnetic field that occurred approximately one million years ago. In the geological time scale it was a "short-term" positive reversal in the then-dominant Matuyama reversed magnetic chronozone; its beginning is widely dated to 990,000 years before the present (BP), and its end to 950,000 BP (though an alternative date of 1.07 million years ago to 990,000 is also found in the scientific literature).