A tree-ringed African lake has yielded a record of Earth's magnetic field spanning the past 150,000 years.
A core of rock and sediment drilled from the bottom of Lake Chala, a picturesque crater lake on the border of Tanzania and Kenya, contains records of the wobbles in the planet's magnetic field. This rock also contains valuable information about the climate over the past 150,000 years, when modern humans were flowing out of Africa, into the Arabian Peninsula and onward to Europe and Asia.
