4. Formation process of life
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  1. Beginning of life

   Life began around 13.500 million of years. We don’t know where it began, nor when or how did it. At least, we could find traces in rocks, because they have a high amount of carbon and other materials, which are considered remainders of living beings. Only microbes has been here from the beggining of the life on Earth, and during the first 1.000 millions of years they were the only ones in the planet. If we looked at the Earth from a powerful telescope, we didn’t see life. The microbes were of a kind which couldn’t resist oxygen, because they were anaerobic beings, and for them oxygen is like poison.

   So, how they lived? There were not plants, only certain elements spontaneously produced in the atmosphere, maybe by the light of the Sun or by a lighting. These elements fell to an ocean where these microbes dwelt. In recent years, thermal vents have been discovered in the bottom of the sea, where volcanic crevices create high-temperature geysers. It is in that environment without Sun light or oxygen where life based on the reactions between particulate materials from the volcanic crevices and sea water.

   These processes last for hundred of millions of years, until life started to change.

  A. Answer with one of these letters: a, b, c. 

  1. How many millions of years have passed since the life on Earth started?

    a. 6.000
    b. 13.500
    c. 28.000

 

  2. There are traces in rocks of

    a. carbon
    b. oxygen
    c. carbon dioxide

 

 3. The first living beings were

    a. jellyfishes
    b. polyps
    c. microbies

 

 4. The first microbies couldn’t resist the

    a. oxygen
    b. carbon dioxide
    c. Sun

 

 5. There are a lot of microbies in

    a. the mountains
    b. the ocean
    c. the Earth’s surface

 

 6. Currently there are primitive microbies in

    a. the mountains
    b. the Earth’s surface
    c. volcanic crevices

 




  2. The first cell

   When a first living cell reproduces, it could suffer from some changes or mistakes. These changes could provoke a higher diversity in the number of living beings, a process we call evolution. The evolution could be related to environmental factors, sunlight radiation, temperature changes or chemical particles. We don’t know how or when it will happen.

   Through a billion of years, the evolution re-shapes different types of microbes, and, in a certain moment, a microbe suffered a curious change: it could use sunlight to combine water and carbon dioxide. There were a huge amount of carbon dioxide in the atmosphere and in the sea water. The microbes which were living in that used sunlight to combine water and carbon dioxide and produced sugars, like starch and cellulose. The process produces the emerging of oxygen.

  All this happened for a billion of years, and these microbes- similar to unicellular seaweeds- were constantly producing oxygen. Thus, the oxygen increased in numbers in the atmosphere. It still was a poison, but there was a huge quantity of oxygen. That happened two billions of years ago, and there were a level of oxygen in the atmosphere similar to the current ones.

   After a few millions of years- we don’t know how many- another mutation change a microbe, which started to use oxygen as a source of energy. The poison is transformed in food and energy. When oxygen suffers a reaction which produces energy, it has as a result more energy that the produced by a combustion without oxygen. Then, life started: groups of cells joined to create something bigger.

   It would be said that these changes took part around 600 millions of years ago. If we would have been watching the coastline, we had seen small animals at first sight. They were small animals similar to our sea worms, without skeleton and with simple functions, because they barely had different organs. They generated more evolved species, like jellyfishes or polyps. These animals, which are still living, have a lack of brain or skeleton, but they perfectly survived.

   It is said that evolution consists on the dissapearance of older beings and their replacement by more modern ones. It is not true. A huge number of living beings are still microbes. Further, we are carrying in our own stomach, in the digestive tract, more microbes than human beings are over the Earth. Microbes, no matter how primitives they are, survive without problems, as other simple organisms- like jellyfishes, polyps or worms without bones- do.

  B. Answer with one of these letters: a, b, c.

  1. The way of reproduction of many living beings is the

    a. evolution
    b. division
    c. multiplication

 

  2. A cell uses sunlight and

    a. air
    b. carbon dioxide
    c. sugar

 

 3. Sunlight and carbon dioxide produce

    a. microbies
    b. cells
    c. sugars

 

 4. Microbies, along with unicellular algae, produced

    a. carbon dioxide
    b. oxygen
    c. starch

 

 5. In the ponds, there were animals like

    a. sea worms
    b. cellulose
    c. starch

 

 6. Every human has millions of microbes inside his

    a. nervous system
    b. locomotive apparatus
    c. digestive apparatus

 




  3. Explosion of life

   600 millions of years ago there was a big explosion of living beings. It is called the Cambric explosion, and numerous living beings appeared then in a short time. It happened in a period of around five million of years, and almost the larger part of basic living creatures appeared then. We still unknow why and how these happened.

   The first creatures had an external skeleton, like clams. In land, there were similar creatures, like insects- for example, beetles-. Complex animals appeared, like crabs, wich still possessed external skeletons. There were also other creatures, very common in these past times, as the ammonites, similar to snails and squids, or the trilobites, with three-segmented bodies. We can watch their fossils in museums.

   And, at last, creatures with an internal skeleton appeared. They are the first fishes, and some of them had some kind of armour. These ones had an external skeleton, but there were their cousins, those with internal skeleton, the ones wich flourished. An internal skeleton provide a spinal column, a defense for the nervous system, the control center of every organ, as the brain. It is also used as an anchor for fins and driving. Finally, a myriad of fish species appeared. Some of then used to move in the coastline, and they started to be out of the water, moving across moisty land with their fins. Then, a mutation developed the amphibians, which could live inside and outside water. They started their life as tadpoles, and later ended living on the land. Some amphibians evolved to more complex forms, giving rise to the reptiles, like lizards or geckos.

   All these lifeforms populated Earth for 600 millions of years, and they also conquered the sea and the land. Thus, life evolves by a variation of genetic codes, from the first living beings which are a single cell to the huge dinosaurs, the kings of our planet for 150 millions of years. They dissappeared 65 millions of years ago, and thanks to that, the human being arose.

  (Original text by F. Manuel M. Carreira S.J. astrophysicist)

  C. Answer with one of these letters: a, b, c.

  1. There were a lot of life beings during the ... explosion

    a. Tertiary
    b. Quaternary
    c. Cambric

 

  2. The clam possesed an ... skeleton

    a. external
    b. internal
    c. it was skeletonless

 

 3. The fossils of big snails are called

    a. insects
    b. ammonites
    c. beetles

 

 4. Fossils with a three-segmented body are called

    a. ammonites
    b. crabs
    c. trilobites

 

 5. From fishes which started to crawl emerged

    a. amphibians
    b. reptiles
    c. salamanders

 

 6. Dinosaurs were the kings of the Earth during

    a. 65 millions of years
    b. 150 millions of years
    c. 600 millions of years

 

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