This has been Dhiman’s first experience working with hard rock because Bangladesh only has loose, young sedimentary rocks. In Meghalaya, India we find extremely old metamorphic rocks - rocks that have been altered under high heat and pressure. We also find igneous rock called basalt that formed from molten rock (magma and lava), and sedimentary rocks such as sandstone and limestone. The sandstone here had millions of years to get compacted and cemented, and it’s so strong that it forms cliffs and giant waterfalls. Limestone is made of shells that have turned into rock.
What secrets can we learn from these rocks?
You remember one: we can learn how the Earth has folded using our compasses to measure the strike and dip! Once we put all our measurements on a map we can learn about the 3-D shape.
Antje’s also been collecting lots of samples of basalt (igneous rock), and she’ll process them in a paleomagnetics laboratory in order to learn about how the rocks have moved (remember that the Earth’s crust is made of plates that move around!). If you’ve ever used a compass, you probably know that Earth has a magnetic field. Magnetic minerals in rocks align with the magnetic field when they form, kind of like little compass needles. Since the Earth’s magnetic field doesn’t vary that much, we can figure out how the rock has moved and rotated since it formed by determining where the magnetic minerals point.
Unlike Bangladesh, Meghalaya has plenty of rocks exposed at the surface. The problem here is that the jungle makes them hard to find! We find the best outcrops along new roads and rivers. We have spent many days hiking through the canyons, climbing our way over huge boulders and getting our feet wet in search of outcrops. The rivers are at the bottom of deep canyons, so we often have to hike many thousands of steps to reach the water.