David Arnold, Museum Volunteer
Sedgwick Museum of Earth Sciences
While the objects that immediately stand out in the Sedgwick Museum are the large dinosaurs, my favourite specimen is much smaller, although far more out of this world. As an undergraduate natural science student at Cambridge I was unsure at the start of my second year which subject to specialise in. We were shown meteorites in one of the first practical sessions of the year. The objects, and the science that has been done using them, absolutely fascinated me.
Meteorites are the remnant fragments of proto-planets which were smashed to pieces right at the beginning of the Solar System, when the planets were forming. These fragments drift through space, and occasionally one of them collides with the Earth. Radiometric dating of specimens such as these provided the first conclusive proof of the age of the Earth and the Solar System. These are therefore the oldest objects in the Sedgwick Museum – at 4.6 billion years old, they are probably slightly older than the Earth itself.
The composition of meteorites is dependent on where in the protoplanets they came from – stony meteorites from the crust or mantle of planets and iron meteorites from the metallic core. My absolute favourites are the stony iron meteorites, which come from the coremantle boundary. The meteorites cooled with green rock crystals called olivine suspended in iron, and are incredibly shiny. At the end of the day, geologists are just people who like shiny things, and the chance to study objects such as these meteorites helped influence my decision to study geology – one that I haven’t regretted for a second.