During the Earth's early history, carbonate sediment formed on the floor of a newly formed ocean. A researcher concludes from this sediment that carbon dioxide was the most abundant gas in the atmosphere. Which is the best evaluation of this conclusion?
Valid, because evidence that much carbon dioxide entered the ocean is sufficient to identify it as the main atmospheric gas
Not valid, because the sediment supports the presence of atmospheric carbon dioxide but does not establish its proportion
Valid, because the amount of carbonate in the sediment reflects the share of carbon dioxide in the atmosphere at that time
Not valid, because forming carbonate sediment transferred carbon dioxide from the ocean to the atmosphere as the Earth cooled
79 exam-style questions on AQA GCSE Chemistry 9.1 The composition and evolution of the Earth's atmosphere, covering 9.1.1 The proportions of different gases in the atmosphere, 9.1.2 The Earth's early atmosphere, 9.1.3 How oxygen increased, and 9.1.4 How carbon dioxide decreased. Each one has a worked solution and a mark scheme showing where the marks go.