The Ordovician was the second period of the Paleozoic era and Phanerozoic eon. It lasted from 488 to 443 million years ago (give or take a million year margin of error). The Ordovician experienced a continued radiation of life, and it witnessed the establishment of the Paleozoic marine fauna while the distinctive Cambrian fauna fizzled out.
During the Ordovician, the southern continents had collected into the ninth super-continent, Gondwanaland. The continents of Laurentia, Baltica, and Siberia were still independent northern continents but Baltica was starting to move towards Laurentia. Gondwanaland was moving southwards which would have effects later on in the period.
Initially the sea level was high and the temperature was warm. Then several volcanic islands chains began releasing carbon dioxide which caused the temperature to skyrocket before it plummeted due to rapid glaciation. The sea levels rose and fell with the temperature causing new shallow seas for plentiful life to form only to be left dried out later.
Life continued to diversify in the Ordovician period. The first true fish appeared, and near the end of the period gave rise to the first jawed fish. The period saw "filling out" the ecosystem with modern and extinct phylum, localization and diversification of global ecosystems and the divergence of deep water and reef habitats. These events are collectively called the Great Ordovician Biodiversification Event(GOBE).
The Ordovician saw the very first true super predator, the giant nautiloid Cameroceras which grew to a massive 30 feet. Trilobites continued to diversity in the Ordovician, but later, the group began its long decline.
Since the Ordovician does not contain a species diversifying event as the Cambrain Explosion, creationists seem to have mostly neglected the Ordovician, though some do pose a few arguments. One is the claim that Bryozoans appeared in the fossil record fully formed with the other major phylum in the Cambrian. This is simply not true, even if one ignores the creationism within it. Bryozoans are, in fact, the only major marine phylum to evolve after the Cambrian originating in the early Ordovician.
A famous fraud is the London Hammer found in Texas which was believed by creationists to come from Ordovician rocks. Actual scientists have concluded that it from the 19th century. With the supposed age coming from the type of sediment it was buried in
Climate change deniers often point to Ordovician glaciers and the high level of CO2 in the atmosphere as proof that CO2 emissions do not cause climate change. This fails to take into account that the CO2 levels fluctuated in the Ordovician and were not present at the same time as the glaciers.