Scientists studying a 10,000-year old ice core noted trends in CO2 concentrations. This graph represents the rough trends for a sample spanning the earliest nine decades represented by the core. Based only on the data in the graph, which of the following would be a valid conclusion? (1 point) The increasing CO2 levels had a nonanthropogenic cause. CO2 levels were higher 10,000 years ago than they are today. CO2 played a greater role than methane in warming trends 10,000 years ago. CO2 levels are increasing at a greater rate today than they were 10,000 years ago. Human activities 10,000 years ago must have contributed substantial amounts of CO2 to the atmosphere.