The Earth's magnetosphere is what protects us from harmful radiation from the sun and other cosmic particles. Without the magnetosphere, there would be increased cancer rates, many navigational issues, and our atmosphere would be slowly stripped away by solar winds.
How the Earth's Magnetosphere was Formed
The Earth's magnetosphere is formed from the conductive metallic alloys from its core, mainly composed of iron and nickel, both ferromagnetic materials. The moving liquid metal generates magnetic fields because of Ampère's circuital law, while magnetic fields in the liquid iron generate more currents that move the liquid by Faraday's law. This feedback loop is called a geodynamo.
How Cosmic Rays are Deflected by the Magnetosphere
Cosmic rays get deflected by the magnetosphere using the Lorentz Force. The Lorentz Force causes charged particles to move in a way that is determined by magnetic fields. Most of the particles that are moving towards the Earth are charged protons (+) and electrons (-) from the sun, which gives the right conditions for the Lorentz Force to be exerted on the particles. The Lorentz Force exerts a perpendicular force onto the particles, causing the particles to spiral in the magnetic fields. Therefore, the Van Allen Belts and auroras borealis are created by the Lorentz Force.
How Cosmic Rays Could possibly Enter the Atmosphere
Even though most of the cosmic rays that are towards the Earth get blocked by the magnetosphere, highly charged cosmic rays with the energy of around 1 GeV, or about enough energy to allow a pea to cruise along at 0.25 millimeters per second (or 2 micrometers a second for a 70 kg human). A proton that has the energy of 1 GeV, however, would be moving at 78% the speed of light. A cosmic ray at this energy level can rip through, ionize atoms, and reach the Earth's surface. They also have a chance to alter the DNA in our cells. However, these are usually very minimal parts and are fixed by our bodies almost immediately. Since the Lorentz Force has less impact on higher energy particles, they are only weakly deflected and therefore most reach the surface of the Earth.
How Bit Flips Happen
If you haven't watched The Universe is Hostile to Computers, which you definitely should, a bit flip can cause many different otherwise unexplainable glitches in computers, such as a plane crash, an altered speedrun, and a triggered election recount. When high energy cosmic rays hit the RAM (memory), changing a 0 to 1 or vice versa by disrupting the charges in the capacitor, or the place that stores the data. It can either add charge or remove charge from a capacitor, flipping the value. Without the magnetosphere, there would be more cosmic rays causing more bit flips to occur.
Conclusion
We are extremely lucky to have the Earth's magnetosphere; without it, life would be extremely difficult as the atmosphere would get slowly stripped away. Even though most particles are blocked, extremely high energy cosmic rays can still reach the surface of the Earth. With the swift advance of technology and space exploration, it is essential to understand the magnetosphere and the effects of cosmic rays without the magnetosphere where such shielding does not exist.