Earth’s Dynamic Shields
SPACE is a dangerous place filled with lethal radiation and meteoroids. Yet, our blue planet seems to fly through this galactic “shooting gallery” with relative impunity. Why? Because earth is protected by amazing armor—a powerful magnetic field and a custom-made atmosphere.
Earth’s magnetic field originates deep inside the planet and stretches far into space, where it forms an invisible shield called the magnetosphere (shown at right). This shield protects us from the full force of cosmic radiation and from dangers emanating from the sun. The latter include the solar wind, which is a steady stream of energetic particles; solar flares, which release in minutes as much energy as billions of hydrogen bombs; and coronal mass ejections (CMEs), which blast billions of tons of matter from the sun’s corona into space. Both solar flares and CMEs trigger intense auroras (shown lower right), colorful displays of light visible in the upper atmosphere near earth’s magnetic poles.
Earth’s atmosphere provides additional protection. An outer layer of the atmosphere, the stratosphere, contains a form of oxygen called ozone, which absorbs up to 99 percent of incoming ultraviolet (UV) radiation. Thus, the ozone layer helps to protect many forms of life, including humans and plankton, from dangerous radiation. Interestingly, the amount of stratospheric ozone is not fixed but is directly proportional to the intensity of UV radiation, making the ozone layer a dynamic, efficient shield.
The atmosphere also protects us from a daily barrage of millions of meteoroids, ranging in size from tiny particles to boulders. Fortunately, by far the majority of these burn up in the atmosphere, becoming bright flashes of light called meteors.
Earth’s shields do not block radiation that is essential to life, such as heat and visible light. The atmosphere even helps to distribute the heat around the globe, and at night the atmosphere acts as a blanket, slowing the escape of heat.
Earth’s atmosphere and magnetic field truly are marvels of design that are still not fully understood. The same could be said of another terrestrial phenomenon—earth’s abundance of water in its liquid form.