Fossils of organisms slightly open secrets of uncountable forms of a life, there is no time occupying the Earth. Studying fossils, scientific trace ways of development of an animal and flora throughout many millions years.
Fossils of organisms serve as the documentary certificate of a life on the Earth. Their spectrum is rather wide - from the hardened fragments of animals and plants to insects, uvjazshih in pitch of coniferous trees which for millions years has turned to amber slices. To traces of ability to live of fossil organisms carry prints of traces of animals and the courses dug by water inhabitants in a sea ground. If enormous skeletons of dinosaurs amaze imagination, microfossils are so small what to make out them it is possible only under a microscope, but they help geologists to find an oil field and gas. However first of all studying of fossils throws light on ways of development of different forms of a life throughout a long history of our planet. On the basis of the extremely incomplete data paleontologists (studying ancient forms of a life) recreate shape for a long time the died out plants and animals, sometimes making amazing opening. So, studying of bones of dinosaurs has shown that these animals suffered from revmatoidnogo an arthritis.
On fossil remains containing in breeds define relative age of various geological layers, and this method is the core in stratigrafii - a science about formation of rocks.
Fossil remains help to restore environmental conditions of this or that geological epoch in which studying is engaged paleoklimatologija, and also a way of life and conditions of dwelling of various animals and plants - a studying subject paleoekologii. They supply us with data on paleogeografii, including about drift (gradual displacement) continents.
Fossils and evolution
English scientist Charles Darvin (1809-82) has put forward the evolutionary theory in the well-known work "+ an origin тшфют" published in 1859. According to its conclusions, many recent animals on the Earth and plants occur from a certain general ancestor, and the first unicells - bacteria and the elementary seaweed which has appeared on the Earth 3-4 billion years ago - eventually have developed in more and more difficult forms of a life.
Process of slow and gradual changes Darwin named natural selection, meaning thereby that at the organisms which have managed better to adapt to external conditions, as a rule, of more chances to survive.
Charles Darvin understood that actual acknowledgement of justice of its theory can give studying of fossils, but in the middle of a XIX-th century found iskopamyh remains was more few to make a complete picture of a life of the most ancient epoch. Thanks to technical progress today our knowledge in the field have considerably extended, having impulsed occurrence of variety of hypotheses about course of evolutionary processes.
In the history of the Earth there were some periods noted more or less sharp jumps in evolution of certain kinds of animals and plants. These sudden jumps scientists name eksplozivnoj evolution.
Similar explosions often followed the periods of mass extinction accompanied by destruction of many groups of organisms, or behind sharp climate changes and an environment, and alternated with the quiet periods from slow evolutionary development.
Sudden change of kinds of plants and the animals, caused by changes of external conditions - we will tell, flooding of huge sites of a land on suburbs of continents and formation of the superficial seas - is called as adaptive radiation and conducts to occurrence of a wide spectrum of the new forms adapted for a life in given conditions.
Trying to define rates of evolutionary changes, especially during the quiet periods of forward development, scientific, in particular, have found out that some kinds of fossil organisms developed faster the others.
The Groups of the died out organisms changing faster other, are called as supervising minerals as help to define age of those zones of geological breeds in which meet. Supervising minerals meet only in any one geological layer. So, on remains quickly changing trilobitov define breeds of a Paleozoic era whereas ammonity carry out the same function in breeds mezozoja. However, according to a number of the scientists, the accelerated evolution of some groups can be only seeming.
Not less important role is played by the theory of evolutionary convergence explaining why some groups of organisms rather far by origin get similarity in a structure and functions. So, judging by fossilized remains of plesiosauri (sea reptiles), they very much resembled fishes.
Many kinds of animals and plants have disappeared from the person of a planet, having left after itself descendants. But in the history of the Earth there were periods when the whole groups of organisms completely disappeared.
The Periods of mass destruction were not so an unusual occurrence. Borders paleozoja (248 million years ago), mezozoja (65 million years ago) and other geological epoch scientists have established, leaning against the periods of mass destruction of plants and animals which evolutionary explosions followed.
Scientists argue for a long time on the reasons of some striking examples of extinction of ancient forms of a life. Most known of them - disappearance from the person of a planet of dinosaurs and other large pangolins in the end of a mesozoic era 65 million years ago. According to one of the newest theories, the Earth has had blow of an enormous meteorite from which in atmosphere dust clouds, for long time hidden the sun have risen, and all reptiles were lost because of the come colds.
Early forms of a life
At all scantiness of geological annals, scientists managed to collect huge volume of the information on evolution of a life throughout all history of our planet.
The Most ancient samples find in breeds age almost 4 billion the years containing microscopic traces of organic acids. Found out the most ancient bacteria lived in Southern Africa and Australia 3,5 billion years ago, and seaweed - 3 billion years ago.
Fossil remains of more advanced besskeletnyh spineless animals, including traces of ability to live in the form of the courses dug by them, find in various breeds late dokembrija. All is representatives ancient bespozvonochnyh though some of them hardly give in to exact classification.
Bespozvonochnye meet, since the cambrian period (about 590 million years ago), since. Many animals of that epoch had skeleton elements - for example, bowls. Behind an exception Arcbaeocyatba (groups of ancient sea animals), all kinds which have appeared in the end of the cambrian period, live and today. However many ancient forms of these animals considerably differ from the present descendants.
In dokembrii, apparently, there was also a first kind of arthropods. In the cambrian period they have been first presented by inhabitants of the seas trilobitami which have died out in the Perm period lasting with 286 to 248 million years ago.
However to the beginning of the Perm period the group of arthropods was represented already also by many other forms of a life, including numerous Crustacea of a being. Today it includes crabs, lobsters and shrimps.
Paleontologists give Important value ostrakodam, to microscopic arthropods rachkam. They have appeared for the first time in late kembrii and serve as supervising minerals for the breeds generated in silure and later periods.
Number of other supervising minerals concern foraminifery, belonging to group of the elementary unicells. As these animals have appeared in the beginning of the cambrian period, it is possible to assume that the elementary organisms have passed a long stage of evolution in dokembrijskie times.
kishechnopolostnyh animals are included Into group modern corals, aktinii and jellyfishes. In the cambrian period this group has been presented by jellyfishes and the hardened corals from which then reeves in warm tropical waters were generated.
The Big variety of fossils molluscs differ. TSefalopody (beings with multichamber bowls) have appeared in the end of the cambrian period and to the beginning ordovika (500 million years ago) have reached wide variety of forms. In the Devonian period (408-360 million years ago) from them have occurred ammonoidy which bowls often meet in adjournment of a mesozoic era (248-265 million years ago).
One more golovonogie - belemnity - have appeared in the coal period (360-286 million years ago). They are ancient ancestors of modern squids and cuttlefishes.
Other group of molluscs - folding - has received the name on number of shutters of their bowls fastened at top. Folding molluscs seldom met till the Silurian period (apprx. 400 million years ago), but subsequently were divided into set of kinds which number includes present mussels and combs. At gastropodov, including modern snails, slugs and trumpeters, a cockleshell are twirled in a spiral. Their geological history has much in common with process of their folding relatives.
One more form of Crustacea of animals - brahiopody. Unlike molluscs, they are rather small presently, however in the ancient time considerably outnumbered molluscs and to value, especially during the period between ordovikom and permju.
Iglokozhie of a being originate in the cambrian period or even earlier. Two major groups of fossil remains are presented by sea lilies and sea hedgehogs. Blossoming of sea lilies has had for a Paleozoic era for then from their skeletons powerful ground adjournment were generated.
Sea hedgehogs have reached a wide variety of forms during an epoch mezozoja, but the peak of their development concerns the cretaceous period which has begun 144 million years ago. Their traces often come across in calcareous breeds, especially cretaceous adjournment generated in the subsequent tertiary period.
One group of animals - graptolity - has appeared for the first time in ordovike, but has completely died out in the coal period. Graptolity lived colonies, however nobody knows, how they looked. At one time scientists carried them to the category kishechnopolostnyh, but now rank them as the most primitive hordovym to beings. The group hordovyh includes also all vertebrate animals.
The fishes who have appeared about 500 million years ago were the First presents pozvonochnymi. And the animals who for the first time have left on a land where plants had time to locate in the Silurian period, became amphibious, occurred from fishes in the Devonian period. Pangolins have appeared in the beginning of the coal period.
Already in the coal period have appeared and flying insects have reached blossoming.
The Rests of flying pangolins have been found out in layers of the Triassic period (213-248 million years ago), and arheopteriks which, according to scientists, became a link between reptiles and birds, - breeds of the end jurskogo the period when on a land dinosaurs dominated. The most ancient bird has appeared about 135 million years ago. Its fossilized remains have been found in China in 1990
The First biped humanoids have arisen about 4 million years ago, however development of human race became the long and slow process, proceeding the last of two million years.