How Living Things Become Fossils

Plants and animals require special conditions in order to be transformed into fossils after they die. Therefore, the chance of one becoming a fossil is very small, and the chance of that fossil being discovered by a human being is even smaller. For an animal or plant to turn into a fossil, it must be buried. If a plant is exposed to the air, it will eventually rot. The bodies of exposed animals will be eaten by scavengers. Sun and rain will eventually cause bones to disintegrate.

On the other hand, if the remains are buried, they will be preserved. Chemicals will enter the animal or plant, causing it to harden. These are the same chemicals that transform sand into rock. When the body of an animal or plant is hardened in this way, it is said to have been fossilized. Many bones are preserved in river and lake sediments. Fossils are also easily formed in caves, where the remains of living creatures become buried by debris that is washed into the caves. Usually, only the hardest parts of an animal or plant, such as the bones of an animal, are fossilized. Once in a while, the soft body parts are fossilized, but this will only happen if they are buried very quickly. This is most likely to occur when a volcano erupts.

Exercises

Complete the sentences based on the articles.

1. The earliest life on Earth … during the Precambrian super eon.

2. The … of the Earth's history, in which we are living today, is known as the Phanerozoic ….

3. Life on Earth … in the oceans.

4. Organic substances coalesced in the oceans to form …, and eventually formed prokaryotic cells.

5. The first living things on Earth were … organisms, known as prokaryotes.

6. Multicellular plants and animals became … during the Phanerozoic eon.

7. The first plants had long cells with thick walls that allowed water to travel up a ….

8. Around 420 million years ago, some marine algae developed the ability to live outside the water, but they still needed to enter the ocean in order to … sexually.

9. Plants and animals … through a number of stages which enabled them to live and reproduce successfully on land.

10. Mosses and … were the first plants to use the wind to assist in reproduction.

11. The evolution of rigid stems allowed plants to grow very tall to … sunlight.

12. Flowers developed as a way of placing the … and … parts of a plant next to each other.

13. … appeared on Earth in the last few million years of the Cenozoic.

14. Scientists think that modern humans … from Africa about one million years ago.

15. Hominid is a group of animals that … humans, chimpanzees and bonobos.

16. X-woman is a young … having lived between about 30,000 and 50,000 years ago whose pinky bone was discovered in southern Siberia.

17. The discovery of X-woman is the first time that DNA … has been used to describe a hominid.

18. Plants and animals require special conditions in order to be transformed into … after they die.

19. Stromatolites are layered structures of … that form in shallow bodies of waters.

20. Only the hardest parts of an animal or plant, such as the … of an animal, are fossilized.

Match the word with its meaning.

1. stage	a) any remains, impression, or trace of a living thing of a former geologic age, as a skeleton, footprint, etc.
2. evidence	b) the actual or hypothetical form or stock from which an organism has developed or descended
3. to survive	c) a part or an individual taken as exemplifying a whole mass or number; a typical animal, plant, mineral, etc.
4. specimen	d) to continue in existence
5. fossils	e) to grow together or into one body
6. to advance	f) mineral or organic matter deposited by water, air, or ice
7. modification	g) to improve or make progress
8. sediment	h) a single step or degree in a process; a particular phase, period, position, etc., in a process, development, or series
9. to coalesce	i) a change in a living organism acquired from its own activity or environment and not transmitted to its descendants
10. ancestor	j) something that makes plain or clear; an indication or sign

Find the missing word.

1. Archaea may been the earliest form of life on Earth.	______
2. Cyanobacteria use the process of photosynthesis in to obtain energy.	______
3. Prokaryotes not have a cell nucleus.	______
4. Roots allow plants to absorb water underground sources.	______
5. Prokaryotes appeared on Earth between about three and a half and four billion years.	______
6. When the Earth first formed, it was extremely hot.	______
7. In 1887 Eugene Dubois uncoveredthe fossil bones belonged to a specimen Pithecanthropus erectus.	______
8. Fossils are likely to appear volcanoes erupt.	______
9. Phanerozoic can be explained "visible life".	______
10. Sexual reproduction is necessary evolution to occur.	______
11. The first flowers appeared Earth grew on magnolias.	______
12. Cyanobacteria also known as blue-green algae.	______
13. Dinosaurs lived the Mesozoic era.	______
14. Mosses and liverworts alternate sexual and asexual reproduction with each generation.	______
15. Insects and plants evolved.	______