Minerals & Fossils

The oldest rock on earth

The oldest dated rocks on Earth are more than 4 billion years old, formed during the Hadean Eon of Earth’s geological history. Such rocks can be found in very few places, like the Canadian Shield, Australia, Africa and in a few other old regions around the world. The ages of these felsic rocks are generally between 2.5 and 3.8 billion years. In 1999, the oldest known rock on Earth was dated to 4.031 ±0.003 billion years, and is part of the Acasta Gneiss of the Slave craton in northwestern Canada. Researchers at McGill University found a rock with a very old age (3.8 to 4.28 billion years ago) in the Nuvvuagittuq greenstone belt on the coast of Hudson Bay, in northern Quebec. Older than these rocks are crystals of the mineral zircon, which can survive the disaggregation of their parent rock and be found in younger rock formations. Three of the very oldest zircons have been found in Australia’s Jack Hills, They date back to almost 4.4 billion years ago. Trace elements in these zircons suggest they came from water-rich, granite-like rocks such as granodiorite or tonalite. That means Earth cooled quickly enough for surface water and continental-type rocks just 100 million years after the moon impact, the massive collision that formed the Earth-moon system.

Rocks and minerals

A mineral is a naturally occurring chemical compound, usually of crystalline form and not produced by life processes. A mineral has one specific chemical composition, whereas a rock can be an aggregate of different minerals or mineraloids.

Minerals are classified by variety, species, series and group, in order of increasing generality. There are more than 5,500 known mineral species.
Minerals are classified by key chemical constituents; the two dominant systems are the Dana classification and the Strunz classification. Silicon and oxygen constitute approximately 75% of the Earth’s crust, which translates directly into the predominance of silicate minerals. The silicate minerals compose over 90% of the earth’s crust. The silicate class of minerals is subdivided into six subclasses by the degree of polymerization in the chemical structure. Other important mineral groups include the native elements, sulfides, oxides, halides, carbonates, sulfates, and phosphates.

read more