We know that the earth is made up of more than just granite and basalt. Volcanoes erupt, bringing materials like mantle xenoliths to the earth"s surface. Seismic waves are able to travel through the earth. Waves that travel deeper in the earth move faster. This is evidence of a change in materials. S-waves that travel too deep never reach the surface. We have evidence on the surface and from seismic waves that the mantle is plastic. Fragments of mantle that are brought up to the earth"s surface without melting. Leftover material from the formation of the solar system. Much more rich in iron than silicates on earth. Made of intrusive igneous and metamorphic rocks. Location where mantle changes from brittle to malleable. Internal melting that causes heavier materials to sink to the center. Samples that come from the centers of exploded planets. Variation in temperature deep within the earth. Earth is about 4. 57 billion years old.