"Sand and gravel make up the most extracted group of materials, even exceeding fossil fuels. Urbanization and global population growth are fuelling an explosion in demand, especially in China, India and Africa. Roughly 32 billion to 50 billion tonnes are used globally each year, mainly for making concrete, glass and electronics. This exceeds the pace of natural renewal such that by mid-century, demand might outstrip supply (see ‘Global scarcity’). A lack of knowledge and oversight is allowing this unsustainable exploitation."