Most marine phyla were unable to manage the transition to land and remain aquatic to this day. Arthropods found a way, and scorpions, spiders, and millipedes were early pioneers. The insect and fish comprise the most successful terrestrial animals today, as fish led to all terrestrial vertebrates. Gastropods made it to land, mainly as and , as did , but the rest of aquatic life generally remained water-bound. Also, many animal clades have moved back-and-forth between water and land, usually hugging the shoreline, sometimes in a single organism’s life cycle, which blurred the at times. The first fish to venture past shore seem to have accomplished it in the , and colonizing land via freshwater environments was a prominent developmental path.
The continental configuration when the Ordovician began was like the Cambrian’s, with . The began . The that would impress modern observers were formed in the Ordovician. Different animals built the corals (, , ) than Cambrian reef builders; but there were no schools of fish swimming around them, as the Ordovician predated the rise of fish. Fish existed (, , ), but they were armored, , and lived on the seafloor. The may have appeared in the Ordovician, but because they had cartilaginous skeletons, the fossil record is equivocal. Some fish had scales, and an eel-like fish might have even had . Teeth and claws were early energy technologies; energy applied by muscles could be concentrated to hard points or plates that could crush or penetrate other organisms or manipulate the environment.
Essay On Vehicular Pollution How To Save Earth
In the earliest days of life on Earth, it had to solve the problems of how to reproduce, how to separate itself from its environment, how to acquire raw materials, and how to make the chemical reactions that it needed. But it was confined to those areas where it could take advantage of briefly available potential energy as . The earliest process of skimming energy from energy gradients to power life is called respiration. That earliest respiration is today called because there was virtually no free oxygen in the atmosphere or ocean in those early days. Respiration was life’s first energy cycle. A biological energy cycle begins by harvesting an energy gradient (usually by a proton crossing a membrane or, in photosynthesis, directly capturing photon energy), and the acquired energy powered chemical reactions. The cycle then proceeds in steps, and the reaction products of each step sequentially use a little more energy from the initial capture until the initial energy has been depleted and the cycle’s molecules are returned to their starting point and ready for a fresh influx of energy to repeat the cycle.