Mismatched mountains

WHAT a striking display of the greatest powers on Earth: layers of rock, stacked over millions of years, ripped apart by tectonic forces. This satellite image is of the Piqiang fault in north-western China. The horizontal stripes are geological layers that have been scrunched up and pushed to the surface by the Indian tectonic plate colliding with the Eurasian plate. In each band of stripes the coloured layers from green  to red  span about 50 million years, capturing  pivotal moments in our planet’s history. Take, for example, the lower green layer, representing the moss blankets that thrived in the Silurian period. It gives way to a thin, pale blue stripe in the middle, formed in the early Devonian, around 400 million years ago. This is when ferns and shrubs came into their own, full of insects and other creepy-crawlies like mites and scorpions. By the mid-Devonian – the large red band – rooted shrubs had cropped up, soon followed by Earth’s first trees. A deep vertical fault line splits the mountains in two. Those to the right of the picture are  sliding northwards at a rate between 5 and 10 centimetres a year – “about as fast as your fingernails grow,” says geologist John Cosgrove of Imperial College London. As you can see, they have been travelling for quite some time. The 3 kilometre offset between them took tens of thousands of years to form.  Catherine Brahic