A high-fidelity geological archive
In the remote Trans-Baikal Krai of Siberia, the sediments at the bottom of lakes in the Chara Basin form a unique natural archive. For millions of years, tiny magnetic mineral grains, carried by wind and water, have settled on the lakebed. As they settled, these particles aligned with Earth's magnetic field, much like microscopic compass needles. Layer by layer, the accumulating sediment has locked in a continuous, high-fidelity record of the planet's geomagnetic history. This field of study is known as paleomagnetism.
Scientific drilling projects in the greater Baikal Rift Zone have extracted sediment cores hundreds of meters long. Analysis of these cores reveals a timeline of the Earth's magnetic field stretching back at least 5 million years. Some studies of deeper cores from Lake Baikal suggest the record may extend as far back as 6.7 million years, with a remarkably constant average sediment accumulation rate of about 3.9 to 4.3 centimeters per thousand years. This steady deposition is what allows for such a clear and unbroken history. Within these layers, every flip of the magnetic poles, a geomagnetic reversal, is visibly recorded as a 180-degree change in the orientation of the mineral grains.