Earth is the third planet from the Sun and the only object in the Universe known to harbor life. We believe Earth was formed over 4 billion years ago, over time we learned many things about it. Earth is the only planet with plate tectonics. Plate tectonics is the theory that Earth’s outer shell is divided into several plates that glide over the mantle, the rocky inner layer above the core. The plates act like a hard and rigid shell compared to Earth’s mantle. Subduction zones and trenches, the polarity of earth, and the age of rocks at mid ocean ridge.German Scientist Alfred Wegener proposed the theory of continental drift – the idea that Earth’s continents move. The processes of subduction and seafloor spreading can change the size and shape of the oceans. Due to these processes, the ocean floor is renewed about every 200 million years. Because of seafloor spreading, the distance between Europe and North America is increasing by a few centimeters per year. This supports the theory of plate tectonics because it shows that plates below sea level move, making continents be more apart from each other. The change in polarity in tectonic plates makes Earth behave like a giant magnet. Earth’s magnetic field is mostly caused by electric currents in the liquid outer core, which is composed of conductive, molten iron. Earth’s magnetic poles have reversed themselves many times during Earth’s history. The last reversal happened 780,000 years ago. Scientists discovered that the rock that makes up the ocean floor lies in a pattern of magnetized “stripes.” These stripes hold a record of reversals in Earth’s magnetic field. The rock of the ocean floor contains iron. The rock began as molten material that cooled and hardened. As the rock cooled, the iron bits inside lined up in the direction of Earth’s magnetic poles. This locked the iron bits in place, giving the rocks a permanent “magnetic memory”. So because of this tectonic plates move and are attracted to each other like magnets.