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Introduction

Fossils are traces of organisms which used to be alive. Fossils can tell us something about the creatures they came from. Hard tissue, such as bone orshell, is fossilized better than softer body parts. This is to be expected, since soft tissue is eaten or it decays soon after death, leaving the bones andshells to petrify (turn to stone).However, examples of perfectly fossilized soft creatures, like jellyfish, do exist. In this section, you learn abouttheories of how fossils form, types of fossils, how fossils are dated, and fossil tourism. People who study fossils are called paleontologists.

Neok12: http://www.neok12.com/Fossils.html

The way fossils form: Interactive site: http://www.flashyourbrain.com/pieces/fossils/index.php

Fossil formation

Different kinds of fossils are formed in different ways. Many form by petrifaction, i.e. turning into stone. The following may petrify:

  • Parts of the body
  • Sediments surrounding the body. Sediments are layers of material (e.g. sand) deposited (dropped) by wind / water / ice.
  • Cavities (spaces) left by the body.

Scientists have observed petrifaction occurring both in nature and in laboratory experiments. Minerals(inorganic compounds) enter the body, hardening it andturning it to stone. Fossilization has been observed to happen very quickly when high concentrations of suitable minerals were present, and when theconditions were favourable for certain bacteria which aid the petrifaction process.

Fossil types

There are several kinds of fossils. These include footprints, dung, moulds, casts, permineralised, and trace fossils.

Footprints, made when creatures walked in soft sand or mud, can be preserved (kept safe) when the sand or mud dries, hardens and then petrifies. From thefootprints we can deduce the shape and size of the feet and how the creature which made them walked. A fossilized dinosaur footprint is shown in Figure 1.

A fossilized dinosaur footprint

Dung can also become petrified. Petrified dung is called a coprolite. From this we can deduce what kind of food a creature ate.

Mould fossils form around a cavity which the organism used to fill. A dead creature can be buried in sediments. These may petrify, forming a mould aroundthe body. The soft body of the creature decays (rots), leaving the mould empty. The shape of the body can be seen from the mould.

Cast fossils look the same as the original body, except that they are made of minerals. Minerals (e.g. calcite) fill the cavity inside a mould, making a castfossil. A cast fossil of a shelled sea animal is shown in Figure 2.

A cast fossil of a shelled sea animal

Permineralized fossils form when the body of an organism becomes petrified. Water moves through the tissues of the dead creature and leaves mineralsbehind. These minerals replace the living tissue. These fossils can give a very good idea of the original structure of a dead creature. A permineralised fossilof a tree stump is shown in Figure3.

Petrified wood. This tree stump turned into stone as minerals replaced the living tissue, and hardened

Questions & Answers

what is mutation
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classification of plants, gymnosperm features.
Linsy Reply
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What is Atoms
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urine is formed in the nephron of the renal medulla in the kidney. It starts from filtration, then selective reabsorption and finally secretion
onuoha Reply
State the evolution relation and relevance between endoplasmic reticulum and cytoskeleton as it relates to cell.
Jeremiah
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Konadu
how is urine formed in human
Rahma
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malaria is caused by an insect called mosquito.
Naomi
Malaria is cause by female anopheles mosquito
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Malaria is caused by plasmodium Female anopheles mosquitoe is d carrier
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a canal is more needed in a root but a cavity is a bad effect
Commander
what are pathogens
Don Reply
In biology, a pathogen (Greek: πάθος pathos "suffering", "passion" and -γενής -genēs "producer of") in the oldest and broadest sense, is anything that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ. The term pathogen came into use in the 1880s.[1][2
Zainab
A virus
Commander
Definition of respiration
Muhsin Reply
respiration is the process in which we breath in oxygen and breath out carbon dioxide
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how are lungs work
Commander
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in the mouth
EZEKIEL
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stimulates the follicle to release the mature ovum into the oviduct
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endocrine secrete hormone and regulate body process
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while pituitary gland is an example of endocrine system and it's found in the Brain
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Biology is the study of living organisms, divided into many specialized field that cover their morphology, physiology,anatomy, behaviour,origin and distribution.
Lisah
biology is the study of life.
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Biology is the study of how living organisms live and survive in a specific environment
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Source:  OpenStax, Siyavula: life sciences grade 10. OpenStax CNX. Apr 11, 2012 Download for free at http://cnx.org/content/col11410/1.3
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