The period of Convalescence is the time during which the person regains health and fully recovers.
Explanation:
- Diseases that can spread from one person to other are called infectious disease.
- Disease development is divided into Incubation period, Prodromal period, period of illness, Decline period, and period of Convalescence.
- During incubation period the pathogen enters the host body and starts multiplying itself. But the signs of diseases are unnoticeable.
- Then comes the prodromal period, when the pathogen keeps multiplying itself and some signs of disease are observed but they are not obvious
- After the prodromal period comes the period of illness when the patient exhibits obvious signs of sickness.
- As the period of illness is over the symptoms of disease start to cease and the the number of pathogen decrease in body.This period is the period of decline.
- Finally comes the period of Convalescence when the person returns to his pre-disease state and is completely healthy. (except irreversible damage caused by the disease)
Answer:
Advanced forms of life existed on earth at least 3.55 billion years ago. In rocks of that age, fossilized imprints have been found of bacteria that look uncannily like cyanobacteria, the most highly evolved photosynthetic organisms present in the world today. Carbon deposits enriched in the lighter carbon-12 isotope over the heavier carbon-13 isotope-a sign of biological carbon assimilation-attest to an even older age. On the other hand, it is believed that our young planet, still in the throes of volcanic eruptions and battered by falling comets and asteroids, remained inhospitable to life for about half a billion years after its birth, together with the rest of the solar system, some 4.55 billion years ago. This leaves a window of perhaps 200-300 million years for the appearance of life on earth.
divine interventionThis duration was once considered too short for the emergence of something as complex as a living cell. Hence suggestions were made that germs of life may have come to earth from outer space with cometary dust or even, as proposed by Francis Crick of DNA double-helix fame, on a spaceship sent out by some distant civilization. No evidence in support of these proposals has yet been obtained. Meanwhile the reason for making them has largely disappeared. It is now generally agreed that if life arose spontaneously by natural processes-a necessary assumption if we wish to remain within the realm of science-it must have arisen fairly quickly, more in a matter of millennia or centuries, perhaps even less, than in millions of years. Even if life came from elsewhere, we would still have to account for its first development. Thus we might as well assume that life started on earth.
How this momentous event happened is still highly conjectural, though no longer purely speculative. The clues come from the earth, from outer space, from laboratory experiments, and, especially, from life itself. The history of life on earth is written in the cells and molecules of existing organisms. Thanks to the advances of cell biology, biochemistry and molecular biology, scientists are becoming increasingly adept at reading the text.
An important rule in this exercise is to reconstruct the earliest events in life's history without assuming they proceeded with the benefit of foresight. Every step must be accounted for in terms of antecedent and concomitant events. Each must stand on its own and cannot be viewed as a preparation for things to come. Any hint of teleology must be avoided.
