Chapter 15, Problem 1SQ

Summary Introduction

To arrange:

The given events in history of life on Earth in order.

Introduction:

In the starting phase of formation of Earth, our planet was filled by reducing gases that did not supported life at the time of evolution of Earth. Evolution of life took place in large seas and oceans in the form of certain micro-organisms like archeabacteria, coacervates. After this event there was production of oxygen gas and thereon the atmosphere of Earth became amicable for supporting life and hence life started.

Answer to Problem 1SQ

Correct sequence:

The theory of origin of life has not been proved till date. It is just a hypothesis. The hypothesis of origin of life can be explained according to the following sequence of events:

(g) Origin of prokaryotes

(a) Accumulation of oxygen in Earth’s atmosphere.

(d) Origin of eukaryotes.

(f) Origin of multi-cellular organisms.

(c) Diversification of animals (Cambrian explosion)

(b) Colonization of land plants and fungi

(e) Origin of humans.

Explanation of Solution

The reason for the above sequence is as follows:

First the life started in sea as aggregation of organic molecules which then gave rise to micro-organisms. The first to be evolved on Earth were archeabacteria then bacteria and other micro-organisms evolved after them. First the micro-organisms survived and gave out reducing gases that were prevalent at that time. Then these micro-organisms started giving out oxygen so in this way there was the evolution and the accumulation of oxygen started.

As the O₂ gas started accumulating then there was the evolution of single-cellular eukaryotic organisms. As the eukaryotic organisms become in good quantity, they began to grow in groups and in this way there was the evolution of multicellular organisms. After this there was evolution of plants and then plants and fungi became to grow in groups or colonies.

Next in this evolution tree was the evolution and development of animals. And after this there was evolution of different types of animals. In this way the diversification of animals that took place. Finally the most highly evolved animal which are humans evolved.

Conclusion

The correct order of evolution was evolution of prokaryotes then accumulation of oxygen in Earth’s atmosphere then origin of eukaryotes then origin of multicellular organisms then colonization of land plants and fungi then diversification of animals (Cambrian explosion) and finally at last, origin of humans took place.