Planet Earth - Ordovician Period

The Ordovician Period spanned from 488 to 444 million years ago. The biodiversity of the marine life continued to expand, especially in the shallower seas where organisms that used calcium carbonate in their shell, with such appearances of arthropods and molluscs. The period also saw the first vertebrate (species with a back bone) family start, namely the fish and some with jaws that evolved in the latter part of the period.  

There were higher sea levels in the Ordovician and at the start period, from around 480 MYA, the climate was very hot due to high carbon dioxide levels within the atmosphere - an early example of the Greenhouse Effect - which led to a potential sea temperature of 45 degrees Centigrade. These levels of water temperature may sound wonderful but it reduced the biodiversity of the more complex (multi-cellular) organisms.

By 460 MYA, the sea temperature had reduced to the types of temperature found in the current equatorial seas. The shallower seas became more inhabited by organisms that exploited the calcium carbonate present in the sea to provide more elaborate shells and body parts. Just think of that, the next time you see a crab, lobster or oyster in the fishmongers.

The marine faunal (means animals) life of this period included some communities of suspension feeders in tiers, which led to the basis of a food chain that still exist today. It is thought that the diversity of marine faunal organisms that share similar characteristics increased fourfold (Dixon, Dougal; et al. (2001) Atlas of Life on Earth. New York: Barnes & Noble Books pp 87)  as well as an increase in filter feeder organisms. The creatures that were typical of the Cambrian period - the archaeocyathids, the eocrinoids, the inarticulate brachiopods, the trilobites were succeeded by the articulate brachipods, the cephalopods and the crinoids by the middle of the Ordovician period. It was also a good time to start scuba diving, if such a thing had been invented, as coral species that create reef-like structures were taking advantage of the calcium carbonate in the water.

But life on the land was restricted to the bryophytes and a few fungal structures (Arbuscular mycorrhiza) that made nutrients more readily available to plant cells - there have been fossils found of hyphae and spores from around 460 MYA.