Rocks!

This is the Hadean Era. On my International Chronostratigraphic Chart it is represented by a magenta blob. 

 Magenta denotes the known unknown of Earth's early days. 

Magenta denotes the known unknown of Earth's early days. 

Forming now on the planet Earth: granite. And cousins of granite: granodiorite (think Plymouth Rock!) and tonalite. No idea what that is. Generally speaking, granite is an intrusive (or plutonic) rock, which means it solidifies below decks. It’s high in silica, as opposed to basalt which is more of an iron situation. Right now, some 500 million years after the birth of the planet, granite is cooling and solidifying beneath the surface of the Earth, then bobbing up through the denser basaltic magma to form the building blocks of continents. There’s quartz in it, silica dioxide, which over time will erode and crumble to make beach sand. There’s plagioclases, white and pink, and mica, shiny black. There are zircon crystals here and there. Over billions of years, as the rock wanders on Earth’s plate tectonic conveyor belts, the granite will deform and compress and warp and stretch — in short, it will metamorphose - into an orthogneiss. In the 1980s it will be in Northwestern Canada, near Yellowknife, where a man named Sam Bowring will chip away at it, finding zircon crystals that will tell him, back in the lab, that these are the oldest known rocks on the planet Earth. More from Sam - a professor now at MIT - in the days to come.