1. The problem statement, all variables and given/known data What is the primary evidence that the Earth's outer core is fluid in nature? (2 marks) 3. The attempt at a solution The Earth has a magnetic field which is created by molten iron that is moving. If there were a solid outer core, there would be no moving iron and no magnetic field. Continental drift - all continents are still drifting and creating volcanoes - this includes the edges under the deep oceans. Is this what one needs to say for two marks, do you think? So is the primary evidence just the Earth's magnetic field? Or can the speed that waves travel at through the outer core also be taken as primary evidence? But what is THE primary evidence? I tried to look this up, but there doesn't seem to be a simple straightfoward answer. Please help. Please do not say that this does not belong in Advanced Physics. This is a question from a third year course and I find it complicated.