The aftermath of the Moon-forming impact left Earth with a hot, CO2-rich steam atmosphere. Water oceans condensed from the steam after 2 Myr, but for some 10–100 Myr the surface stayed warm (~500K), the length of time depending on how quickly the CO2 was removed into the mantle. Thereafter a lifeless Earth, heated only by the dim light of the young Sun, would have evolved into a bitterly cold ice world. The cooling trend was frequently interrupted by volcanic- or impact-induced thaws.
The Variscan orogen formed between 380 and 300 million years ago through several accretionary and collisional cycles, culminating with the construction of the Pangea supercontinent. This process occurred via sequential opening and closure of oceanic basins, synchronous detachment of Gondwana derived continental ribbons, and their outboard amalgamation onto the Laurussia margin. The Variscan orogen is rather unique compared with other orogenic belts on Earth: its overthickened and dominantly magmatic crust in the central belt, surprisingly minor mantle involvement in the magmatic and geodynamic processes, coherent and pulsed magmatism along the collision suture, and its complex accretionary history. Because its final product, Pangea, is the youngest and best-understood supercontinent on Earth, the Variscan orogeny offers clues for understanding the mechanisms of supercontinent formation.
