EARTH’S CYCLES FOR MAN’S BENEFIT

14. When we see deterioration and death all around us, what question naturally arises as to our own life?

¹⁴ Some persons ask: ‘What about the fact that all living things tend to deteriorate?​—that the cells and tissues break down, so that old age sets in, culminating in death? Would not this always continue to take place with human life?’ Let us see.

15. What would be the situation on earth if nothing decayed, broke down, or changed in its composition?

¹⁵ All physical things on earth tend to break down with age. Rocks crumble. Wood decays. Think, though, what the situation would be if there were no effect of weather on rocks, wood, and other material, and if there were no decay of organic matter. That would mean that the earth would be sterile. Few, if any, chemical reactions could take place. Our digestive systems could not function properly, because they operate by chemical and bacterial action, breaking down and changing the composition of food. Little work could be done, because few things could be altered in structure. Even now certain plastics that are not easily decomposed are causing a waste-disposal problem.

16. (a) What changes in matter are essential for life to exist on earth? (b) In what way is man different from animals with regard to the reason that humans die?

¹⁶ For earthly life to continue, then, there must be changes in organic and inorganic matter. Cycles of birth and death were originally purposed for every living thing on earth, with the exception of mankind. Why except mankind? Because man was made in God’s image and likeness. Only humans, not animals, can be called God’s “sons” and “daughters.” Not of animals, but of man, it is said that ‘death entered in through sin.’​—Genesis 1:27; Romans 5:12.

17, 18. What are some of the cycles essential to the continuance of life on earth?

¹⁷ Consider some of these cycles. There is plant life that provides food for all animal life, and, in fact, is the basis for all earthly life. Plants can do something that animals cannot​—they manufacture their own food by the use of sunlight. This process is called “photosynthesis.” Animal life must therefore depend on plant life. Plants must grow, supply food and die. Then, through the marvel of seed germination, another crop is produced.

¹⁸ In the sea the “food chain” maintains life on various levels; the tiny vegetable phytoplankton are food for the animal zooplankton, which, in turn, feed the larger fish, including some that serve as food for man. Then bacterial action converts dead matter into food for the phytoplankton, and the cycle begins all over again.

19, 20. Explain how, even though cells and tissues break down, a human could live forever.

¹⁹ In the process, individual animals die, to be replaced by offspring, thus preserving the species. What, then, is the hope for continued individual human existence? Is there a difference in this respect between man and animals?

²⁰ Yes, there is. For, while cells and tissues in living bodies suffer wear, and some cells die, life tends to reverse the “running-down” process. Living things make highly organized, complex compounds out of more simple ones. If the life-force could be kept operating at full efficiency, worn tissues would continually be replaced or repaired. Old age would not set in, and the person would never die. Only the Creator can accomplish this in humans. He promises everlasting life to obedient men and women. All the earth’s cycles​—among them the birth and death of plant and animal life—​are actually arranged primarily for mankind’s ultimate benefit.

21. (a) What evidence do we have that, even with imperfection, human life was once much longer than it is in our time? (b) Why is man’s life-span shorter now than in the earliest periods of mankind’s history?

²¹ The Bible record reveals that humans were made to live much longer than animals. The early offspring of Adam, being near to perfection, lived as long as 969 years. This illustrates the fact that cell-replacement continued for all those years, and the cells of the central nervous system (which scientists say can be repaired but not replaced) were maintained in healthy repair during centuries of living. (Genesis 5:27; see also verses 5-31; 9:29.)

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OXYGEN CYCLE

Plants take in carbon dioxide, give off oxygen

Animals and humans take in oxygen, give off carbon dioxide

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NITROGEN CYCLE

Lightning combines nitrogen with oxygen. Rain brings this to earth

Green plants provide food for animals and humans

Bacteria act on decaying plants and animal manure, release nitrogen back into air. Other bacteria produce plant food

Bacteria take nitrogen from the air for plants’ use