The fossil remains of animals with body plans recognizable as arthropods, echinoderms, mollusks, and other bilaterians first appeared during the Period, around million years ago.

              The fossils remains of arthropods, Echinoderms, Mollusk and other bilaterians appeared in Cambrian period and throughout the Paleozoic era.

Explanation:

                      Trilobites were marine group of arthropods that appeared in the Cambrian Period around 55.6 million years ago, eventually becoming extinct during the Permian Period. Most of the organisms were  small, bottom-dwelling organisms that had fed on small organic matters in sediment on the sea bottom. The body is divided in three segments: head (cephalon), middle (thorax), and tail (pygidium). Many species had large, compound eyes. Fossils had define characters of having body divided in to head,thorax,and tail. Body had segmentation and citineious body layer.

a fossil fuel is a fuel formed by natural processes, such as anaerobic decomposition of buried dead organisms, containing energy originating in ancient photosynthesis.[1] the age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years.[2] fossil fuels contain high percentages of carbon and include petroleum, coal, and natural gas.[3] other commonly used derivatives include kerosene and propane. fossil fuels range from volatile materials with low carbon to hydrogen ratios like methane, to liquids like petroleum, to nonvolatile materials composed of almost pure carbon, like anthracite coal. methane can be found in hydrocarbon fields either alone, associated with oil, or in the form of methane clathrates.

the theory that fossil fuels formed from the fossilized remains of dead plants by exposure to heat and pressure in the earth's crust over millions of years was first introduced by andreas libavius "in his 1597 alchemia [alchymia]" and later by mikhail lomonosov "as early as 1757 and certainly by 1763".[4] the first use of the term "fossil fuel" was by the german chemist caspar neumann, in english translation in 1759.[5]

in 2017 the world's primary energy sources consisted of petroleum (34%), coal (28%), natural gas (23%), amounting to an 85% share for fossil fuels in primary energy consumption in the world.[6] non-fossil sources in 2006 included nuclear (8.5%), hydroelectric (6.3%), and others (geothermal, solar, tidal, wind, wood, waste) amounting to 0.9%.[7] world energy consumption was growing at about 2.3% per year. in 2015 about 18% of worldwide consumption was from renewable sources.[8]

the supermassive black hole is in the middle of the galaxy.