Meteorites
Authors: Wang Kun , Korotev Randy 
Published: September 2017

For thousands of years, people living in Egypt, China, Greece, Rome, and other parts of the world have been fascinated by shooting stars, which are the light and sound phenomena commonly associated with meteorite impacts. The earliest written record of a meteorite fall is logged by Chinese chroniclers in 687 bce. However, centuries before that, Egyptians had been using “heavenly iron” to make their first iron tools, including a dagger found in King Tutankhamun’s tomb that dates back to the 14th century bce. Even though human beings have a long history of observing meteors and utilizing meteorites, we did not start to recognize their true celestial origin until the Age of Enlightenment. In 1794 German physicist and musician Ernst Chladni was the first to summarize the scientific evidence and to demonstrate that these unique objects are indeed from outside of the Earth. After more than two centuries of joint efforts by countless keen amateur, academic, institutional, and commercial collectors, more than 60,000 meteorites have been catalogued and classified in the Meteoritical Bulletin Database. This number is continually growing, and meteorites are found all over the world, especially in dry and sparsely populated regions such as Antarctica and the Sahara Desert. Although there are thousands of individual meteorites, they can be handily classified into three broad groups by simple examinations of the specimens. The most common type is stony meteorite, which is made of mostly silicate rocks. Iron meteorites are the easiest to be preserved for thousands (or even millions) of years on the Earth’s surface environments, and they are composed of iron and nickel metals. The stony-irons contain roughly the same amount of metals and silicates, and these spectacular meteorites are the favorites of many collectors and museums.

After 200 years, meteoritics (the science of meteorites) has grown out of its infancy and become a vibrant area of research today. The general directions of meteoritic studies are: (1) mineralogy, identifying new minerals or mineral phases that rarely or seldom found on the Earth; (2) petrology, studying the igneous and aqueous textures that give meteorites unique appearances, and providing information about geologic processes on the bodies upon which the meteorites originates; (3) geochemistry, characterizing their major, trace elemental, and isotopic compositions, and conducting interplanetary comparisons; and (4) chronology, dating the ages of the initial crystallization and later on impacting disturbances. Meteorites are the only extraterrestrial samples other than Apollo lunar rocks and Hayabusa asteroid samples that we can directly analyze in laboratories. Through the studies of meteorites, we have quested a vast amount of knowledge about the origin of the Solar System, the nature of the molecular cloud, the solar nebula, the nascent Sun and its planetary bodies including the Earth and its Moon, Mars, and many asteroids. In fact, the 4.6-billion-year age of the whole Solar System is solely defined by the oldest age dated in meteorites, which marked the beginning of everything we appreciate today.