What is Planet Earth?

The ground beneath our feet seems to be the most solid and unchanging thing we know. It forms foundations for our cities and an environment in which we can live. Yet in reality, Planet Earth is spinning on its axis and hurtling through hostile space, as it orbit the nuclear furnace of our Sun. It is an active, dynamic, living planet.

The rock-solid surface is not as solid as it appears. The Earth has 3 well-known layers. Earth has an inner core of solid rock, which is mostly iron. The temperature here is probably around 4,500 C. Beyond the inner core is a layer of liquid rock, called the outer core, which extends halfway to the surface. Beyond this is a thick layer of rock called the mantle, which is partly molten and runny. The thinnest layer, or crust, is on the Earth's surface, floating on the red-hot liquid mantle. The crust is about 6 km thick under the oceans, but 30-40 km thick beneath the land.

The seemingly rock-solid surface of the Earth is cracked like giant slabs of crazy paving. Earthquakes shake our cities and volcanoes erupt, giving clues to the fiery movements beneath the grounds. From above, the planet is buffeted by radiation and particles streaming at it through space. But in between is an atmosphere, and oceans with liquid water, and temperature which are just right for life.

To an alien spacecraft travelling past the solar system, Planet Earth would immediately stand out as something special. The composition of the atmosphere, with free oxygen and traces of gases like methane can only be sustained by life. The aliens might detect the characteristics colors of chlorophyll, the pigment used by plants on land and algae in the sea to trap sunlight. If our aliens were not careful they would pick up the radio cacophony of our broadcast, revealing that life here is at least moderately intelligent.

Life has transformed Earth and Earth continues to support life. Buried in the rock s are minerals, gems and precious metals. Using energy from Earth in the form of coal and oil, we have transformed into the artifacts of civilization from books and building to cars and computers. We all depend on Earth.