Why the Moon’s initial magnetic field may be responsible for life on Earth

The habit of a planet depends on many factors. A strong and long-lived magnetic field exists. These regions originate in their liquid cores thousands of kilometers below the surface of the planet and spread to space, removing the atmosphere from harmful solar radiation.

Without a strong magnetic field, a planet struggles to rotate on a breathless atmosphere – which is bad news for life as we know it. A new study published in Science Advance suggests that the now extinct magnetic field of the Moon may have helped protect our planet’s atmosphere as life was formed around 4 billion years ago.

Today, the Earth has a strong global magnetic field that protects the atmosphere and low-orbiting satellites from harsh solar radiation. In contrast, the Moon does not have either a breathless atmosphere or a global magnetic field.

Global magnetic fields are generated by the motion of molten iron in the cores of planets and moons. The fluid needs energy to keep moving, such as the heat trapped within the core. When there is insufficient energy, the field dies.

Without a global magnetic field, charged particles of the solar wind (radiation from the Sun) passing close to a planet generate electric fields that can accelerate charged atoms, called ions, out of the atmosphere. This process is occurring on Mars today and is resulting in a lack of oxygen – something that has been directly measured by Mars’ atmosphere and the Unstable Evolution (Maven) mission. Solar wind can also hit the atmosphere and knock molecules into space.

The Maven team estimates that throughout its history the amount of oxygen lost from the Martian atmosphere is contained in a global layer of water 23 meters thick.

[Read: The Moon’s surface is rusting — and Earth may be to blame]

Ancient magnetic fields test

New research shows how the early regions of the Earth and Moon would have interacted. But examining these ancient areas is not easy. Scientists rely on ancient rocks that have small grains that are magnetized as rocks, saving the direction and strength of the magnetic field at that time and place. Such rocks are rare and require careful and delicate laboratory measurements to extract their magnetic signal.