This image shows a type of igneous rock called granite.
Click on image for full size
Image from: C. Alexander
Meanwhile the seeds of continents called the "continental shields" began to take shape. The material which makes the continents is lighter and more bouyant than other crustal material, somewhat like the granite shown in this picture. It took awhile for continental material to form. The oldest known rock of continental type is thought to be 3.2 BY old. The oldest continental material is called the continental shield.
This is page 9 of 10
Shop Windows to the Universe Science Store!
Our online store
includes issues of NESTA's quarterly journal, The Earth Scientist
, full of classroom activities on different topics in Earth and space science, ranging from seismology
, rocks and minerals
, and Earth system science