but seriously those crazy scientists just make stuff up surely looking at that explanation lol
I must not have explained it adequately. Though just because you do not understand something doesn't mean those that did the work are making it up. That can be extrapolated to wherever you like.
Let me start again: The basics of canyons is that they are erosive features. That is, they are produced by wearing the rock away. That rock is removed from the scene by water and all you are left with is essentially a really long hole. In geology when you are determining the age of a rock unit or strata you are looking at material that has been deposited (or emplaced) at the site. The problem with canyons is that the process of formation involves the removal of material so you are just left with rock in place that was there before the canyon was formed and hence older.
At the Grand Canyon what has been done historically is that they have gone down stream and looked at the places where this eroded material is deposited. There is a place called the Great Wash which is a site where the river spreads out into a large basin/plain. When the river spreads out it slows down, and as it slows down it loses the energy to carry or transport rocks, sand and silt. This site has been extensively investigated and it has been determined that the oldest of this material was laid down around 6Ma. From this they have deduced that the canyon began forming or eroding 6Ma ago.
Recently another group of scientists began looking at minerals in the canyon with a new technique that allows them to determine how long ago these minerals were exposed at or near the surface. In other words how long ago all the rock that sat above was removed/eroded. Their work showed that the oldest times when these minerals were exposed was around 70Ma.
70Ma is a lot older than 6Ma. Now the evidence for the 6Ma is not nullified by the 70Ma age. It still represents a valid period of erosion. What you can infer from the 70Ma age is that there was an older period of erosion that pre-dated the 6Ma event.
When the geologists look at other palaeo-evidence of what that part of the USA was like at the time it tells them that at that time the rivers flowed in the opposite direction to the current direction. That is the land was tilted the other way. 70Ma ago the Pacific Plate was pushing its way under (subducting under) the North American Plate, making lots of volcanoes, starting the Rocky Mountains and producing porphyry copper deposits and epidermal gold. It was quite a different place.
Now if the rivers flowed in a different direction the eroded material would have been deposited in a different place to the 6Ma material. And 70Ma is a long time the stuff that was eroded my have been eroded again.
Anyway what is postulated that the canyon that was produced in the 70Ma event was re-used and made much bigger by the 6Ma event that produced the Grand Canyon as we see it today. Though as the water flow direction was opposite the only depositional evidence we see associated with the Grand Canyon is from the erosion event that started 6Ma ago.
So can you see that there is no need to make stuff up? The Grand canyon can have been formed by two different erosion events/periods. And very probably more than two periods.
