A lot vs. Alot: 9 Grammatical Pitfalls
1708, "pertaining to the Silures," from Latin Silures "ancient British tribe inhabiting southeast Wales." Geological sense is from 1835, coined by Sir Roderick Impey Murchison (1792-1871) because rocks of this period are especially frequent in Wales.
The third period of the Paleozoic Era, from about 438 to 408 million years ago. During this time glaciers that formed during the late Ordovician melted, causing sea levels to rise. The first coral reefs, fish with jaws, and freshwater fish appeared, and jawless fish continued to spread rapidly. The first vascular plants also appeared, as did land invertebrates including relatives of spiders and centipedes. See Chart at geologic time.