When the Earth's oceans first formed, large amounts of atmospheric carbon dioxide dissolved in the water. Marine organisms incorporated the dissolved carbon into their shells and skeletons. Over millions of years, these shells compressed at the bottom of the ocean to form a sedimentary rock, permanently locking away the carbon.
What is the main chemical compound in these shells, and what is the name of the sedimentary rock formed?
Calcium carbonate (CaCO3\text{CaCO}_3CaCO3), forming sandstone
Silicon dioxide (SiO2\text{SiO}_2SiO2), forming limestone
Calcium carbonate (CaCO3\text{CaCO}_3CaCO3), forming limestone
Calcium sulfate (CaSO4\text{CaSO}_4CaSO4), forming gypsum
97 exam-style questions on Edexcel GCSE Chemistry 9.2 Earth and atmospheric science, covering 9.2.1 The Earth's early atmosphere, 9.2.2 How the atmosphere evolved, 9.2.3 Chemical test for oxygen, and 9.2.4 The greenhouse effect and climate change. Each one has a worked solution and a mark scheme showing where the marks go.