Earth’s magnetic field is a protective blanket. It keeps charged particles from the Sun and beyond from hitting the surface and much of the atmosphere, where they could cause a lot of problems. But it’s a lumpy blanket. It doesn’t provide the same level of protection for the whole planet. Instead, the magnetic field has peaks and valleys.

Today, there’s a deep “valley” over parts of South America and the South Atlantic Ocean. Known as the South Atlantic Anomaly, it allows particles in Earth’s radiation belts to come closer to the surface than anywhere else.

That’s a big problem for orbiting spacecraft. Some have been damaged when they passed through the anomaly. The International Space Station has extra shielding to keep its crew safe.

About 3,000 years ago, there was a big “peak” in the magnetic field over the Middle East. The field was stronger than usual there, and stayed that way for centuries.

Some of the most recent evidence for it came from bricks from Mesopotamia, around present-day Iraq. The bricks contain bits of iron oxide. When the bricks were fired, the iron particles recorded the condition of the magnetic field at the time. The bricks also contained the seals of kings. Archaeologists know just when the kings ruled. That allowed scientists to piece together the magnetic history of the region — confirming a big “lump” in Earth’s ancient magnetic field.

More about the magnetic field tomorrow.

Script by Damond Benningfield