The overall structure of Mars is well documented thanks to observations made by scientists. However, without setting foot on the planet, we only know about it through observation. For this reason, the question of plate tectonics on Mars is a controversial issue. While scientists are sure that Mars' core is not active, meaning there is no plate tectonics; they cannot be sure that there never was a time when there was. Mars was formed by materials released by the first solar nebula. The core of Mars has a radius of 1,300 to 1,500 km and is not active. The lack of movement of the core results in a lack of magnetic field on the planet and a lack of plate tectonics. Mars formed very quickly and the extent of its accretion led to global melting. This allowed iron-rich molten material to settle in the center of the planet, forming a core separate from the mantle, filled with silicate. The lack of a moving core means that there is no magnetic field on Mars. However, the Mars Global Surveyor mission, which ran from 1996 to 2001, observed broad bands of magnetic anomalies on the crust, indicating that a magnetic field once existed. Loss of heat and solidification of the core caused the magnetic field to stop. Allan Hills 84001, a meteorite discovered in Antarctica in 1984, contained 3.9 to 4.1 billion year old carbonates that contained magnetized minerals, indicating that Mars had a magnetic field for the magnetic field. The cores of Earth and Mars share certain similarities, which can be attributed to the two planets being terrestrial and differentiated planets. Both have a central metallic core, composed of iron and nickel, surrounded by a silicate mantle. The similarities, however...... middle of paper ......iveScience." Current news on space, animals, technology, health, environment, culture and history | LiveScience . Web. May 03, 2011. "Plate Tectonic on Mars - Evidence of the magnetic field | GEOLOGY.COM." Geology.com - Earth Science News, Maps, Dictionary, Articles, Jobs. Web. May 3, 2011. "Science Magazine: Connect." Science. Web. May 3, 2011. "Science News: Plate Tectonics ...on Mars." Student Research Libraries. Web. May 3, 2011. .Shirley, James H. and Rhodes Whitmore Fairbridge. Encyclopedia of Planetary Science. Berlin [etc.: Springer, 2006. Print.