BRIEF REVIEW OF LIVING WORLD IN SPACE, TIME AND PHYLETIC LINEAGE

Living World In Space:

Living world of today is enormous in size. It has been reproducing and evolving since the time of its origin on this planet. Today almost all parts of the world abound in living organisms. The distribution of organisms in space can be studied through biomes. A biome is a large regional community primarily determined by climate. It has been found that the major type of plant determines the other kind of plants and animals. These biomes have, therefore, been named after the type of major plants or major feature of the ecosystem. The major biomes of the world you will study in the chapter of ecology.

Living World in Time:

Since the time of origin of life on this planet, various organisms were evolved and dominated this planet during various periods of geological time chart. This has been found by the study fossils which allow biologists to place organisms in time sequence. A geological time passes and new layers of sediments are laid down; the older organisms are in deeper layer, provided sequence of layers has not been disturbed. Therefore, the fossils found in the same layer must have been younger layers. In addition it is possible to date or age the rocks by comparing the amounts of certain radioactive isotopes they contain. The older sediment layers have less of these specific radioactive isotopes than the younger layers. A comparison of layers gives an indication of the relative age of the fossils found in rocks. Therefore, fossils found in same layer must be alive during the same geological period.

Phyletic Lineage:

When we look at the biodiversity (the number and variety of species in a place), we find that there are nearly 2,500,000 species of organisms, currently known to science. More than half of these are insects (53.1%) and another 17.6 % are vascular plants. Animals other than insects are 19.9 % (species) and 9.4 % are fungi, algae, protozoa, and various prokaryotes. This list is far from being complete. Various careful estimates put the total number of species between 5 and 30 millions. Out of these only 2.5 million species have been identified so far.

The life today has come into existence through Phyletic lineages or evolving populations of the organisms living in the remote past. Evolutionary change often produces new species and then increases biodiversity. A phyletic lineage is an unbroken series of species, arranged in ancestor to descendant sequence with each later species having evolved from one that immediately preceded it. If we had a complete record of the history of life on this planet, every lineage would extend back in time to the common origin of all early life. We lack that record because many soft bodied organisms of the past had not left their preserved record as fossils.