Animals-Creation

With due considerations given to the study of circumstances under which life was formed in general , and creation of animals on Earth in particular,we rely on the study of fossils belonging to animals that existed and have ever since become extinct during various geological periods.

The beginning environment of the Earth was not only inappropriate for life but also defied it.And this situation seems to have continued until about a thousand million years after coming into existence of the Earth.Although there are some signs of life found in fossils belonging to 3800 million years ago and also some cells that belong to " Eukaryotic " beings found in fossils dating back to 1400 million years ago , excavations and researches in geology confirm coming into existence of an obscure form of life during late "pre-cambrian" period ) the long period of geological history between the formation of the Earth , now estimated on the basis of meteorite analysis to have occured 6.4 billion years ago,and the beginning of the phanerozoic Eon,about 600 million years ago). Remains of a kind of jelly fish , some worms and " arthropods " discovered in 630 million year old rocks in Southern Australia attest to that claim.

" Cambrian " period ) this period began 345 million years ago and ended about 515 million years ago ( has coincided with considerable transformation in life. Presence of shelled invertebrates " Echinoderms " and " Molluses" in this period has been proven.Up to now 006 genera of animals have been seen in fossils which belong to this period , of which " Trilobites " are the most significant. During " Ordovician " period ) this period began 515 million years ago and ended about 435 million years ago (. Great expansions occured among animals,many of whom evolved rapidly and spread all over the oceans.In the early part of this period animals with calcareous organs such as "Jelly Fish" and "Rugose Corals" proliferated. An abundance of "Vertebrates" are discovered in fossils found in Colorado related late Ordovician period which apparently are the oldest of their kind . Primitive " jawless fish " ( Agnatha ( also belonged to this period. Of the most notable events of the late " Paleozoic " period ) from 600 million to 255 million years ago ( was the advent of land animal communities . Towards the late " Devonian " period ) from 408 million to 363 million years ago ( the first amphibians which resembled fish appeared." Trilobites " became extinct towards the end of " Permian " period ) from 280 million to 225 million years ago ( and instead " Snails " evolved rapidly . During " Carboniferous " periods ( from 363 million to 286 million years ago ) reptiles which did not differ a lot in comparison with amphibians evolved rapidly; insect , also appeard in this period and spread." Mesozoic " period's ) from 032 million to 65 million years ago ( significant event was the appearance of " Mammal like " creatures which eventually led to real mammals . Dinosaurs were among the most important reptiles of the period. Developed dinosaurs are divided into two major enotherm groups: 1 - Lizards: whose body structure is an indicaton of their belonging to reptiles , and 2 - Birds (ornithis-chian( whose major characteristics were high movement capability and giant bodies. They appeared during Jurassic period ( from about 190 to 135 million years ago ). Dinosaurs had also lived in marine environments and some had even possessed flight organs which could possibly be considered as the forerunners of today's birds.The biological face of the Earth was entirely altered with " Mesozoic period " coming to an end,and a vast pack of animals ceased existence due to changes in their living conditions . The largest apparent change on earth dates back to 65 million years ago.When,dinosaurs,which ruled the Earth more than 150 million years ago without any rivals,faded away and were replaced by more intelligent and agile beings.The sudden increase in temperature , scarcity of food due to receding seas, dried up lagoons and an increase in the number of other creatures are some of the proposed opinions relating to the cause of the sudden extinction of Dinosaurs.And it was from that time on that most of the present day animals emerged and developed.

From the time that intelligent man ( homo-sapiens ( came into existence and throughout the centuries afterward,he has had a close relationship with animals and has used them variously for food , other needs ,etc. And to utilize them even more so , he has always tried to have a better understanding of them . It seems that Aristotle ) 384 - 322 B.C. ( must have been the first zoologist to have performed extensive scientific research about animals and to have presented the first classification of such. He classified the animals based on the existence or lack of their blood circulation systems. It is notable that about 1.5 million kinds of animals and half a million types of plants have been identified in existence on earth in our time.