2.6 Saskatchewan Time Scale By erincampbell564 1 CE Humans come to North America 1 CE Bison come to North America 50 Climate changes and SK plateau develops 65 Dinosaurs are extinct 75 Shallow sea begins to retreat 213 SK is covered by shallow sea (again) 220 First mammals 245 First dinosaurs 248 Mass extinction in the oceans 90% of the species disappear 355 First amphibians 385 Potash is deposited in the shallow sea that covers SK 470 Tyndall Stone deposited as massive limestone 478 Meteorite hits SK leaves a crater called the "Carswell Meteorite Crater" 544 SK covered by epicontinental Sauk Sea hard shelled invertebrates includes Trilobites 1700 Erosion of the mountains 1800 Earth changes from an anoxygenic environment to an oxygenic environment 1850 Wathaman Batholith an intrusion of magma under the surface 1900 Volcanoes in SK 2100 Break up of ancient continent creation of a large ocean 2500 SK is part of a large continent 4600 Earth is formed