How to find out what was on earth before man?

Human history, we know from written sources, historical records, which survived until our days. But writing in the WHO Nickle 3.4 millennia to P. X. (Egypt, Mesopotamia). And Earth, as is known, has in its age of about 5 billion years! Even if all you can learn from the same written evidence? Sometimes more than books tell discovered during excavations of the ancient things, objects used by the first man. For the historian, archaeologist it is often crucial. For geology - a science that studies the history of the planet - bowels of the earth play a role of written documents. " Indeed, in terrestrial strata remains of life that can "tell" what this life was not thousands, but millions of years ago. In the bowels of the earth can be found traces of rain and sea waves, winds and ice. On deposits of rock, scientists restore the contours of the sea, rivers, swamps, lakes, deserts, distant past. How could survive to this day the remains of organisms past? Even such distant from us - for millions of years? When a body falls into a river, lake or foreshore of the sea, he quickly covered with silt, sand or clay. Soaking salts, the remains of organisms "kameneyut. And in this way they are today, scientists say. They may be the skeleton and the other surviving parts of the animal to recover not only the look, but also his lifestyle. Modern methods and techniques allow one of only a part of the skeleton (skull, jaw, leg bones) to restore the vertebral structure of his body closest relatives among both fossil and among modern animals. The data of geology and paleontology (the science of fossil animals and plants) will systematize the accumulated knowledge. They became the basis of dividing the history of life on Earth into five segments, which are called eras. Each era is divided into periods, and the period - on the epoch and age. Each of them took place different geological events and changes in the development of wildlife. The oldest is the Archean era. It began about 3.5 billion years ago and lasted for 1.6 billion years. In its place came the Proterozoic era (beginning - 1.9 billion years ago). The era in which we live - the youngest. It is called the Cenozoic - a new era of life. That era began 70 million years ago and continues today. Established thanks to the study of sedimentary rocks of the crust (sand, clay, limestone, etc.). Upper layers - the youngest, and the lower - so they are older. The preserved remains of organisms in them was genuine life on Earth in the distant past. But to establish the exact date is not enough study of Earth's crust. Original "geological clocks" have helped create physicists and chemists. They discovered that the atoms of certain elements - uranium, thorium, radium - all the while changing. This change is called "decay." At the same time producing other items. Such a transformation is accompanied by radiation (the release or emission of small particles) and the process is called radioactive decay. He always runs with the same speed. Different elements of the uneven rate, and hence the time of complete disintegration. For example, rubidium-87 decays in about 50 billion years, uranium-238 - for 4.5 billion years. But radium - for 1590 years. Constant for each radioactive element decay rate are allowed to use them as an accurate clock to measure the age of rocks. And to determine the shortest time learned to use the radiocarbon method. Indeed, in the tissues of living organisms found along a common carbon (atomic weight 12) small amounts of the isotope. This is the same substance, but its atomic weight is 14. Its half-life - 5760 years. Check, this method was by comparison with dated archaeological sites.