How does magnitosphere protect life on the earth?

Answer 1

The magnetic field of the Earth tends to deflect charged particles that are directed towards Earth and thus provides important protection from the radiation associated with such particles.

The magnetosphere originates as the Earth's magnetic field which is shaped and modified by the solar wind, i.e. the stream of charged particles constantly emanating from the Sun, and the result of the two is called the magnetosphere.

(One might prefer to say that it is the Earth's magnetic field, rather than magnetosphere, that protect the Earth from most radiation, but they are really combined and it is not obvious how one distinguishes the ultimate resulting protection as being from one thing or the other. )

The protection depends on the type of particle and the type of protection. One can think of several examples of relevant phenomena; solar wind, cosmic rays, and solar flares with coronal mass ejections.

Cosmic rays are affected by the magnetosphere, but the predominant influence on cosmic rays comes from the Earth's atmosphere. The magnetosphere is capable of deflecting low energy cosmic rays away from Earth. The higher energy cosmic rays have collisions in the atmosphere create new particles and ionizing radiation that are unhealthy for life on Earth. The magnetosphere provides some protection from cosmic rays.

Without the Earth's magnetic filed, there would be a complete transformation of the magnetosphere, to the point that it would not exist in the sense that it does now. In such an event, the Earth's atmosphere would encounter direct collisions with the solar wind and and cosmic rays and there would be "atmospheric stripping" by the solar wind. One initial effect would be the loss of the ozone layer and the associated protection from the UV light from the Sun. Of course, more atmospheric loss over time would ultimate make life impossible, an even which seems to have occurred on Mars after its magnetic field disappeared.

Solar flares are often accompanied by a coronal mass ejection (CME) that consists of a large number of energetic charged particles. Sometimes these particles are directed towards Earth and encounter the Earth's magnetosphere and create what is called a geomagnetic storm. Depending on the size of the event, this creates a radiation hazard. Without the magnetosphere the CME would interact directly with the atmosphere and one might expect even more serious consequences for life on Earth.

For these various reasons, one can say the magnetosphere is essential for continued life on Earth.