Two theories about the Earth's early atmosphere give different proportions of gases. A student says that the theory with more supporting evidence must be the correct one. Which is the best evaluation of the student's statement?
Not valid, because a theory can be replaced when new evidence is found
Valid, because scientific theories are always based on strong evidence
Not valid, because no evidence about the early atmosphere can be found
Valid, because the amount of evidence decides how useful a theory is
40 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.