FST - 1

6th Part

Q.  What is carbon dating? How is the age of fossils determined?   

A.  With the developing knowledge of radioactivity more accurate dating of fossils and certain types of rocks has become possible. Radioactive substances can be easily detected using certain instruments. The method most commonly used, now, for estimating the age of fossils is radio-carbon dating. Radioactive isotope of carbon is commonly known as carbon- 14. Since carbon- 14 is chemically the same as ordinary carbon, both arc absorbed by plant and animal tissues in the same proportion as they are present in the atmosphere as carbon dioxide. Plants use this carbon dioxide in making their food. Animals eat plants. Hence, the proportion of carbon- 14 in the tissues of plants and animals is the same as in the atmosphere, as long as the plant or the animal is living. But as soon as it dies, no more carbon can enter its body as photosynthesis or food intake stops. Following death, the carbon-14, already present in the body, decays steadily into ordinary carbon. So the smaller the number of carbon-14 atoms remaining, the older is the fossil. Thus, if we take a piece of ancient wood or bone and measure the amount of carbon-14 present in it, we can estimate the age of the material. This technique has been applied to materials of known age, and thus its accuracy was tested giving confidence in the method to determine the age of unknown objects. The carbon-14 method is applicable only to organic materials which still contain carbon. It cannot be used for fossils in which all organic matter has decayed. In that case, the age of the fossil can be estimated by determining the presence of other radioactive elements like fluorine, or phosphorus.

Q.  Role of radioisotopes in dating the past. 

A.  With the developing knowledge of radioactivity more accurate dating of fossils and certain types of rocks has become possible. Radioactive substances can be easily detected using certain instruments. They have built-in "clocks" in the form of 'radioactive isotopes' that change or decay at a constant rate into non-radioactive form. If this rate of conversion is known, then it is easy to estimate the age of a fossil by measuring the quantities of the radioactive isotopes and the non-radioactive ones into which they have changed in the rock. For example, Uranium is transformed into certain isotopes of lead which are not radioactive. So, the age of uranium-containing rocks can be determined by determining the amount of Uranium left or decayed into lead.

Q.  Name in a sequence the four main stages of human evolution. Which out of these showed bipedal posture for the first time?         

A. The main stages of human evolution are as follows - 

Hominids - The earliest human-like or hominid remains come from two separate East African sites (3.5 million years ago) Ethiopia and Tanzania (3.75 million years ago). It is concluded that these earliest hominids were built with an ape's head on top of a man-like body. They show hominid characteristics to place them firmly within human ancestry. There is evidence that they walked on two feet. 

'Homo Habilis-The First Tool Makers - One of the most important developments in human evolution was the dramatic expansion in brain size. Certain specimens recovered from deposits in East Africa apparently have brain capacities in excess of 650 cm" and close to 800 cm3. These specimens represent the first appearance of our own kind and were termed Homo habilis. The species name Homo habilis, means, literally, handyman. Homo habilis walked upright. The bones of the hand, while displaying many characteristics of modern humans, are somewhat curved in places and more robust than in modern man, i.e. Homo sapiens. The leg and foot bones have characteristics that are both ape-like and human-like, but overall, they are much closer to those of modern humans than to apes. The leg and foot were those of a habitual two-footed animal. The simultaneous occurrence of Homo habilis fossils and crude flakes and stone tools indicate that they used tools.

Homo Erectus

Homo erectus or the erect man first arose at least 1.6 million years ago and continued to live for more than a million years before the transition to Homo sapiens occurred. Homo erectus had a large brain measuring 800 to 900 cm" Fossils of Homo erectus have been discovered throughout Africa, Europe, and Asia. Signs that Homo erectus hunted animals and ate meat are available from the stone tools they used and the marks which these tools left on the bones of animals which have been recovered near their own dwelling areas. There is evidence, that the life of Homo erectus must have been fairly complex and these individuals are considered as intelligent, socially interacting beings. One can even imagine that a relatively complex spoken language may have evolved. The prehistoric record is, of course, silent on this point.

The Neanderthals

These were the first human-like fossils found. The Neanderthals existed throughout western Europe and across into the near east and central Asia from about 100,000 years ago to 40,000 or 35,000 years ago, depending on the precise locality. There are, striking structural similarities between Neanderthals and modern humans. Although the posture, range of movements and manipulation skills were the same in Neanderthals as in modem humans, the skeleton was substantially more robust. Neanderthal's brain was on average slightly larger than normal for modern humans, measuring about 1400 cm3. Neanderthals were proficient hunters, skilled toolmakers and they used hides for protecting their bodies. For the first time in human history, ritual burial became common.

Homo Sapiens-Modern Human Beings

Discoveries of a number of fossils of Homo sapiens suggest that modern humans arose in Africa and migrated to the rest of the old world via the Middle East. It should be noted that these modern humans of the early upper stone age, 40,000 years ago, were distinctly more robust or sturdy as compared with the population today.

Q.  Describe the evidence that supports the various theories proposed for the evolution of modern man.                                   

A.  The general theory of evolution of man is based on evidence that is provided from different sources, such as the fossil records of animals which lived in the past, similarities found in the developing embryos of primates and of other animals, the archaeological remains of the past and their dating and more recently from biochemical studies. Cave paintings and other artifacts left by the early human beings speak of their social and cultural life.

Palaeontological - Palaeontological evidence, of their existence, is left in the form of skeletons and bones buried in the rocks. These are known as fossils. Crucial evidence of human evolution is provided by the study of these fossils. Sometimes, the buried body and the skeleton of an animal disintegrate entirely. If the surrounding material is sufficiently firm, a cavity may remain, having the exact outlines of the structures that disappeared. Such a cavity is called mold, Similar to molds are the impressions. These are left by extinct objects or parts of the body upon the surrounding material. The impression is made while the surrounding material is soft, like footprints in clay or lava. Footprints of extinct animals are also impressions giving valuable information about the animals that made them.

Archaeological Evidence

The study of human antiquities, especially of prehistoric period is known as archaeology. The biological and cultural evolution of man proceeded side by side and the two influenced each other. Like the physical remains of man, his cultural remains also lie buried in the ancient deposits. Often, the two categories of evidence are found together in the same layers of the rock. With the passage of time and the increasing capacity of his brain and development in other bodily organs, man's culture became more and more varied and complex. He learned the use of new materials for making tools and developed new techniques for improving them. The use of tools had a tremendous impact on increased access to food and therefore on cooperative living in colonies. In many areas, archaeological remains show reindeer to be the principal source of meat they ate.

Anthropological Evidence

Modern humans arose at a time when the Earth was going through a very cold and icy period called the Ice Age, which began about 75,000 years ago and ended about 10,000 years ago. The Ice Age was at its most severe about 18,000 years ago, the time which coincides with the development of prehistoric art. This art is represented by colourful images painted on cave walls and rock shelters. Many thousands of carved and engraved pieces of bone and ivory have also been discovered from the same period. A large majority of images are of animals which we can recognize, especially images of reindeer and bisons are plentiful; while paintings of people are strangely absent.

Biochemical Evidence -

Biochemical studies show us that, as evolution proceeds and the species get differentiated, they accumulate changes in the structure of their proteins and DNA. Longer the separation time, the greater the changes. These changes are expressed in terms of percent genetic distance which indicates the proportional difference between the DNA of the two species. Comparative studies of the proteins of the African apes and humans showed that chimpanzees, gorillas, and humans are closely related to one another.

Q.  Who is lucy             

A. The partial skeleton of a 20 years old hominid who lived more than three million years ago was found by Dr. Donald Johanson in Ethiopia. The fossil remains, are known as 'Lucy'.

Q.  List five astronomical methods being used to explore the universe.   

A.  Optical Astronomy - The easiest method of studying light from a cosmic object is to collect it through a telescope and record it on a photographic plate. Photographic films are exposed for long periods of the time-sometimes night after night-to the light being collected by a telescope aimed at distant stars. This method of collecting and investigating light from the cosmos is called optical astronomy.

 Radio Astronomy - Radio astronomy, i.e. the study of cosmic objects through radio waves emitted by them. The radio telescope, a basic tool of radio astronomy, collects radiations from space in the radio wave region. One of the largest radio telescopes in the world was designed and set up by Indian astronomers at Ootacamund. The other radio telescopes in India are stationed at Gulmarg, Ahmedabad, Gauribidanur near Bangalore.

Meteorites - Meteorites entering the Earth's atmosphere from time to time. They bring us many messages about the cosmic objects from which they were chipped off.

Observatories in Space

With the coming of the Space Age, observatories equipped with telescopes and cameras could be placed right in space, beyond the Earth's atmosphere. An observatory in space may be in the form of an orbiting satellite like the Unmanned Orbiting Solar Observatories, Orbiting Astronomical Observatory, Skylab, Einstein Observatory, IRAS (Infra Red-Astronomy Satellite) and many others. An observatory may also be stationed on the Moon or any other planet having suitable temperature and other conditions. Instruments are also put aboard high flying balloons, rockets and aircraft are to record observations. These observatories can record radiation from a cosmic object in the regions of the spectrum such as the IR, UV, gamma rays and X-rays do not penetrate the Earth's atmosphere.

Visiting the Neighbouring Worlds

As space research came of age, it became possible for us to send spacecraft to other planets & even land men & instruments on the Moon. These ventures also provided a rich stock of information about the Solar System. For instance, astronauts of the Apollo mission to the Moon brought back lunar rocks & soil samples, photographs of the lunar surface and Ieft several instruments there for further study.