Oldest bit of Earth yet found!Zircons are tough little devils! They’re hard (7.5 on the Moh&rs

Oldest bit of Earth yet found!Zircons are tough little devils! They’re hard (7.5 on the Moh’s scale), do not melt or metamorphose easily (the melting point of zircon is over 2500 C), essentially they’re nearly indestructible. So, when a zircon is born from some magmatic event (or the melting of a previous solid rock), they tend to record for all posterity the oxygen isotope ratios of their general environment, and include enough uranium-thorium-lead to provide a geochronometric clock.This little zircon has apparently been hanging around for ~4.4 billion years. Okay, its dark blue core is 4.4 billion, the clear growth (also zircon) surrounding it is about 1 billion years younger. This means it originally crystallized ~114 million years after the original formation of the Earth from the solar nebula! It is considered the oldest little bit of the Earth yet discovered.Zircons provide the best tools known so far for following early Earth history: studying zircons of various old ages can show an evolution of oxygen ratios that indicate when conditions suitable for life were developed, even possibly suggesting the presence of liquid water. The fact that the zircons exist at all indicates that a solid silicate rock-based (rather than magmatic ocean-covered surface) was already in existence. In younger geologic environments, such as today’s Mid-Atlantic Ridge, some old zircons of 300 million years in age and even 1.6 billion years in age have been recovered hosted in recent lava eruptions: these are taken to indicate the “recycling” nature of the Earth’s lithosphere. Those indestructible little zircons have somehow made it from older continental sources, through the plate tectonic cycle, and have returned to the Earth’s surface via volcanic activity.Why blue? Most blue zircons that you buy as jewelry are heat treated to change the zircon’s original color (usually a mucky red brown) back to a pristine-appearing sparkling colored gem. But blue zircons can occur naturally (possibly a natural heat treatment with that clear zircon rim was added?). Oh, by the way, another fun fact about zircons is that they’re fluorescent in ultraviolet light! This zircon is being viewed in ultraviolet light so that it fluoresces, that way scientists can see the layering in the crystal and figure out which corner of it grew first. This zircon was located in a gneiss craton in Western Australia, where other very old zircons have also been located. If you like the Archean, read our Earth Story post: http://tinyurl.com/mgdfhstAnnie RPhoto downloaded from the NPR article: http://www.pbs.org/wgbh/nova/next/earth/4-4-billion-year-old-crystal-is-the-oldest-piece-of-earths-crust/Also read is you wish:http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2075.htmlhttp://www.nature.com/nature/journal/v393/n6686/full/393676a0.htmlhttp://minerals.gps.caltech.edu/files/Visible/zircon/Index.htm__ -- source link

More pics about