Boundary|Time|Surface: Assessing a meeting of art and geology through an ephemeral sculptural work

Thank you for your comments and changes required for the finalization of our paper: “Boundary|Time|Surface: Assessing a meeting of art and geology through an ephemeral sculptural work”. We have completed the requested changes, renumbering figures where necessary and changing the layout of the figures. We attach below a version of text document with changes tracked. The results of these changes will be shown in the revised ‘clean’ manuscript and figures pdf. There is also a new version of the supplement, to make sure all the cross-references are correct and as required.

1. Introductory and didactic displays from Gros Morne National Park Discovery Centre gallery exhibition.
Incorporates images from the following public domain sources: Lapworth, C.: On the Tripartite Classification of the Lower Palaeozoic Rocks, Geological Magazine, new series, 6, 1-15, 1879. In the 1800's, the periods of the geologic time scale were thought to reveal natural chapters in Earth history, so Murchison and Sedgwick believed that boundaries should be drawn at important changes between rock layers. When they discovered the lower part of Murchison's Silurian System overlapped with the top of Sedgwick's Cambrian System, the two men had a furious argument that ended their friendship and collaboration.
Geologists have been dividing time into periods, like "Cambrian", "Ordovician" and "Jurassic" since the early 1800s. There are no rocks at Green Point that can be dated with radioactive isotopes. However, in other parts of the world, volcanic rocks occur between strata with some of the same fossils. From this evidence, we know that the Cambrian ended and the Ordovician began about 485 million years ago.
Our understanding of time has advanced since Sedgwick, Murchison, and Lapworth. Radioactive isotopes allow geologists to estimate the ages of rocks in millions of years. Isotopes work well for igneous rocks (formed by melting), but not with most sedimentary rocks (deposited in layers on the Earth's surface). For sedimentary rocks, geologists often use the occurrence of new fossil species to figure out when the rocks formed.

Correlating the Time Scale Globally
Early geologists typically placed boundaries at times of great environmental change. This often meant parts of the record were missing, so comparisons across different continents became difficult, as a result. Modern geologists have re-defined most of the boundaries between periods at places called stratotypes, chosen in continuous successions of strata containing many fossils. Green Point is the stratotype for the Cambrian-Ordovician boundary.
Physicists like Marie Curie discovered radioactive elements, which allowed some rocks to be dated in millions of years.
Although the Ordovician sea was teeming with life, the land was very different from now; there were no large land plants or animals at that time. Fish-like relatives of primitive vertebrates, called conodonts, lived in the sea. Only their microscopic teeth are preserved as fossils. The species Iapetognathus fluctivagus appeared just before the first abundant graptolites.
In 2001, geologists chose Green Point in Gros Morne National Park as the stratotype for the boundary between Sedgwick's Cambrian and Lapworth's Ordovician. The boundary was placed at the first appearance of the conodont fossil Iapetognathus fluctivagus, found all over the world in rocks of this age. The establishment of the boundary was marked by a ceremony on the shore.
Later in the Ordovician, about 470 million years ago, the rocks at Green Point were involved in a collision of tectonic plates that started building the Appalachian mountain range. Inside the new mountains, the horizontal layers were folded and steeply tilted, so that Cambrian rocks are now on top of the Ordovician. Millions of years of erosion by glaciers and waves have exposed the layers again, so that we can see them in the spectacular cliffs and coastline.