Meteorites: ‘rocks’ from space
Dr Vic Pearson (UK) Every year, thousands of tonnes of dust and rock penetrate the Earth’s atmosphere. The fiery passage of these objects produces the familiar ‘shooting star’ phenomenon, known as meteors. Much is destroyed during this descent, but some material is delivered to the Earth’s surface, either as meteorites or micrometeorites (the latter being typically less than 1mm). However, only 1% of the surviving material is large enough for identification and recovery, making meteorites and micrometeorites much sought after, both scientifically and commercially. Fig. 1. Meteors, or shooting stars, are a regular sight in our skies. Not all survive atmospheric entry but produce spectacular fireballs. (Image courtesy of A. Danielson.) Naturally, bombardment by extraterrestrial materials has been ongoing throughout Earth’s history. The early Solar System would have been a turbulent time and the young Earth was subject to much greater amounts of extraterrestrial infall than today. Our geological record contains many impact craters, and fossilised meteorites have been found in Ordovician sediments in Sweden (Schmitz et al., 2001), thought to be the result of the catastrophic break-up of an asteroid 470 million years ago. Today, it is accepted that the majority of meteorites are fragments of asteroids broken off during collisions with other extraterrestrial objects, perturbed from their orbits by the gravitational effects of Jupiter. The origins of micrometeorites are less well constrained and evidence abounds for both cometary and asteroidal origins. Types of meteorites Meteorites are generally classified as either falls or finds. Falls are those that are … Read More
