Downward

The order, and why it is this one

Join anywhere. Each stop carries the route with it, so the foot of every question here offers the next one and the way back to this page.

1. 01What is inside the Earth?What we know about the inside of this planet comes mostly from earthquake waves passing through it, read against laboratory experiments. Mantle rock lies under the crust and has been sampled where tectonics lifted it to the surface or where a piece came up inside a diamond, and two continent-sized structures near the core have no agreed explanation.Deepdepth, meaning: Major unanswered questions.Uncertain. Meaningful scientific, historical or philosophical disagreement remains.Read
2. 02When did the continents start moving?That the plates move now is not in doubt and is measured directly. When the process started is argued from indirect evidence in very old rocks, and proposed dates range from more than four billion years ago to less than one, depending on which signature is accepted as diagnostic.Deepdepth, meaning: Major unanswered questions.Uncertain. Meaningful scientific, historical or philosophical disagreement remains.Read
3. 03How deep does life go?A biosphere exists inside the crust, in rock and sediment, running on chemistry rather than sunlight and, where energy is scarce, at metabolic rates so slow that its biomass turns over in centuries to millennia. Its extent and its total mass are estimated from sparse sampling, and the estimates are wide and have been revised sharply downward.Deepdepth, meaning: Major unanswered questions.Uncertain. Meaningful scientific, historical or philosophical disagreement remains.Read
4. 04What lives under the ice?Liquid water exists under the Antarctic ice sheet, in lakes and in water moving along the bed beneath it. A 2013 expedition drilled into one such lake with a microbiologically clean drill and found a working microbial ecosystem living on minerals in the dark.Shallowsdepth, meaning: Interesting questions with substantial evidence and real uncertainty remaining.Known. Strongly supported by evidence and broadly established.Read
5. 05Is Earth’s magnetic field about to flip?Reversals are recorded in the rock and the current field is measurably declining, which is why the question keeps being asked. The decline has happened before without a reversal following, and no method exists for forecasting one.Shallowsdepth, meaning: Interesting questions with substantial evidence and real uncertainty remaining.Uncertain. Meaningful scientific, historical or philosophical disagreement remains.Read