The sun's massive power source has two main disadvantages -- ultraviolet light and the solar wind. Ultraviolet light can cause cancer, cataracts and other health problems. The solar wind, a stream of charged, or ionized, particles that stream off of the sun, could strip away our atmosphere. Fortunately, the Earth has some natural defenses against both. Our ozone layer protects us from ultraviolet (UV) light, and our magnetic field protects us from the solar wind.
The stratosphere, the layer of atmosphere just above the one in which we live, contains a thin layer of ozone (O3). This layer wouldn't exist without the sun. Ozone is made of three atoms of oxygen. It's not a very stable molecule, but it takes a lot of power to create it. When UV light hits a molecule of oxygen (O2) of, it splits it into two atoms of oxygen (O). When one of these atoms comes into contact with a molecule of oxygen, they combine to make ozone. The process also works in reverse -- when UV light hits ozone, it splits it into a molecule of oxygen and an atom of oxygen.
This process is called the ozone-oxygen cycle, and it converts UV light into heat, preventing it from reaching the surface of the Earth. Without the sun, the Earth wouldn't have an ozone layer -- but without the sun, the Earth also wouldn't need it.
But while the sun creates the ozone layer, the Earth itself creates its defense against the solar wind. Without the Earth's magnetic field, ionized particles from the solar wind could strip the planet's atmosphere away. This magnetic field comes from deep inside the Earth's core. Interactions between the inner and outer core create the magnetic field.
The planet's inner core is made of solid iron. Surrounding the inner core is a molten outer core. These two layers are very deep within the Earth, separated from its crust by the thick mantle. The mantle is solid but malleable, like plastic, and it's the source of the magma that comes from volcanoes.
The Earth's inner core spins, much like the Earth spins on its axis. The outer core spins as well, and it spins at a different rate than the inner core. This creates a dynamo effect, or convections and currents within the core. This is what creates the Earth's magnetic field -- it's like a giant electromagnet. When the solar wind reaches the Earth, it collides with the magnetic field, or magnetosphere, rather than with the atmosphere.
The poles actually change places periodically -- about 400 times in the last 330 million years. The field weakens while the shift takes place. But computer simulations predict that the sun might come to the rescue, interacting with the atmosphere to supplement the magnetic field, while the shift is in process.
The Earth's physical composition generates its magnetic field. That composition is a product of the Earth's creation, which would not have been possible without the sun.