Gary Gilligan has replied to the first post, June 14th, and raised some interesting points about silica, and to the apparent violent history of Mars. The link provided, at http://finance.yahoo.com/news/scientists-find-something-mars-could-19010… … actually implies that on earth tridymite forms at extremely high temperatures in an explosive paroxysm known as silicic volcanism (and Mount St Helens is cited as an example). It then says these volcanoes form as a result of plate tectonics – plates shifting on earth's outer shell dive deep into the earth's Mantle, carrying water with them. They melt within the Mantle and as molten rock, or magma, are brought back up to the surface, exploding and flowing out. The combination of a high silica content and extremely high temperatures in these volcanoes creates the tridymite. Obvioulsy, the problem is that Plate Tectonics do not occur on Mars – or is tridymite telling us it does, or has occurred in the past? Or is it telling us that tridymite forms under altogether different circumstances and conditions? The latter is the most obvious route to explore first of all, and I'm sure this is what will happen (and is happening as we will see at the back end of this post).
The same story can now be read at http://phys.org/print385109290.html … a team of US based researchers have been studying data sent back from Mars by Curiosity Rover and were surprised to find tridymite, a type of mineral usually associated with explosive volcanoes etc. To date, planetary scientists have thought the geological history of Mars has been fairly tame on the basis it does not have shifting plates that lead to big earthquakes and explosive volcanoes. Those volcanoes known from Mars are of the steady flow type – not the explosive big bang volcano such as Mount St Helens.
Whilst none of these researchers question Plate Tectonics theory on earth one must wonder if it will be questioned by non-mainstream geologists. At the same time one can't imagine mainstream knocking Plate Tectonics Theory as they would have to come up with another explanation for big earthquakes and whopper volcanoes – so the field is wide open for an enquiring mind to sift through the evidence and come up with a different explanation.
Plate Tectonics theory is closely bound up with various other beloved aspects of uniformitarianism – such as the 100,000 year Milankovitch cycle and Ice Age theory. The latter will be defended mercilessly. Heretics beware. Wegener's theory of Continental Drift was sliced up and dismantled and subsequently subsumed into Plate Tectonics theory which gelled perfectly into the idea of uniformitarianism, a slow and ongoing process (with the odd explosive volcano to wake the world up from stupor and general boringness). One has also to bear in mind that Milankovitch showed that a tilt of the earth could theoretically create an Ice Age. He demonstrated this could be done even in the uniformitarian model (which held total sway in the early 20th century) but it is quite clear the same thing applies in a Catastrophic model. We might then ask, how would that impinge on Plate Tectonics theory?
At www.astronomy.com/news/2016/06/ancient-volcanism-may-have-been-very-hot-… … tridymite is described as a silica mineral that could only be formed as a result of high temperature volcanism on Mars. The last volcano to erupt on Mars is dated, currently at 20 million years ago – way back when. It tells us that as there are no plates the 'hotspots' of volcanic activity remain fixed on the surface as evident by the Thursia bulge. The volcanic activity is thought to come from melting hot mantle plumes underneath the Martian crust. At NASAs Johnson Space Center a team are trying to make tridymite by geological processes at lower temperatures – at temperature levels low enough to be attributed to your average volcano (rather than the explosive variety). If they manage to do that it will be a different ball game, they say, and Plate Tectonics will emerge unscathed (we might add).