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9.3 Environments through time: 4. Exploiting new environments
Extract from Earth and Environmental Science Stage 6 Syllabus (Amended October
2002). © Board of Studies, NSW.
[Edit: 23Jul08]
Prior Learning: Preliminary Module 8.2 (subsection 5).
Science Stages 4-5 syllabus: Outcome 5.8 (content: 5.8.3 -
the theory of evolution and natural selection), Outcome 5.9 (content: 5.9.2 - the theory of plate tectonics and 5.9.4 -
natural events).
Background: The fossil record is scattered with examples of organisms that look very similar to present-day organisms. Evolution is the process used to explain this phenomenon. As new environments evolved due to changes in atmospheric, aquatic or terrestrial conditions organisms would move into these new environments and either survive by adapting to the new conditions or perish and become extinct. As organisms adapted they would gradually evolve into forms that could make best use of their new environment due to natural selection.
outline the theory of evolution by natural selection
Darwin's theory of natural selection (Kimball's Biology Page, USA) is summarised by the following.
- Each organism must face a constant "struggle to survive" and those best adapted to their environment will survive best.
- A species produces more offspring than can possibly survive.
- There is variation within a species population and some individuals have types of variations that favour their survival.
- Organisms that survive will pass their favourable characteristics on to future generations.
- The environment selects those individuals best suited for survival by the mechanism of natural selection.
outline evidence that present-day organisms have developed from different organisms in the distant past
- The fossil record generally shows a progression from simple life forms to complex life forms.
- Comparisons of present-day organisms with fossils of organisms of the past show changes that have occurred over time.
- The distribution of similar plants and animals across the world suggests that after the break-up of the supercontinents, evolution continued, resulting in small changes to species in response to changing environmental conditions.
- Similarities in anatomy, embryology and biochemistry of the vertebrates suggest that they are descended from a common ancestor.
gather and analyse information from a geological time scale and secondary sources to identify and date the major evolutionary advances made by plants and animals
Select a suitable geologic timeline from which to gather the required information. Many appear in text books. The following are web-based versions, most of which provide links to further information.
- The geological time scale
Enchanted Learning Software, EnchantedLearning.com, USA. - The
evolutionary timeline
TalkOrigins Archive, National Center for Science Education, USA.
A good way to analyse information is to structure it in a table. Well-designed tables assist you to identify trends, patterns and relationships. Make your own time scale as a table. Using the geologic time scales you have selected, identify the major evolutionary advances made by plants and animals and include them on the scale.
| Eon | Era | Date | Evolutionary advances | |
|---|---|---|---|---|
| Plants | Animals | |||
gather information from secondary sources to summarise the features and distribution of some of the first land plants, amphibians and reptiles
The information for this point could be gathered in point form into a table like the one shown below. The following web sites will provide most of the information you need to collect. Refer also to texts such as The Cambridge Encyclopedia of Earth Sciences, chapter 22 Fossils and evolution (See reference in Resources button, top left).
- How plants
conquered the land Hans' Paleobotany Pages, Ellecom, The Netherlands
- First amphibians Westfield State College, Massachusetts,
USA
- Reptiles (see Living reptiles and their fossil relatives)
Paleontological Museum, University of Oslo, Norway.
Suggested table organisation for the collation of information
| Features of first land plants | Distribution | |
|---|---|---|
| Name | Features | |
| Features of first amphibians | Distribution | |
|---|---|---|
| Name | Features | |
| Features of first reptiles | Distribution | |
|---|---|---|
| Name | Features | |
gather information from secondary sources to compare the diversity and numbers of organisms from a fossil site
Gather information about a particular fossil site.
Many Internet sites, such as those identified below, provide suitable information.
- Fossil sites of Australia Australian Museum, Sydney
- Riversleigh
Fossils
ABC, Australia
Alternatively, you may like to extract information from a video such as that referenced below.
- Video Reference: Message in the Rocks, Audio Visual Unit,
UNSW, Sydney 2052, telephone 9385 3913.
- Recognise that numbers of organisms at a fossil site is a different concept to the diversity of species at a fossil site.
- Construct tables to record the numbers of organisms and the diversity of organisms at the selected site.
outline the major steps in the expansion to the terrestrial environments by land plants, amphibians and reptiles
- The early to middle Ordovician period was characterised by warm
weather and high atmospheric moisture.
- At the end of the Ordovician, Gondwana was located
at the South Pole with massive glaciers forming, causing shallow seas to drain
and sea levels to drop.
- Colonisation of the land occurred during the Ordovician and
microfossils of cells, cuticle (waxy covering on leaves) and spores of early land plants
have been found.
- Land plants leave their first fossil traces in the Ordovician
period but vascular plants are not known until the Silurian.
- The climate of the Silurian stabilised and the large glacial
formations melted leading to a substantial rise in sea levels.
- There was a wide and rapid spread of jawless fish. There was also
the appearance of the first freshwater fish and the first jawed fish. In many ways, the
freshwater fish were well adapted for life on the land. They only now needed a large
gaseous exchange organ and a more efficient means of locomotion.
- Land had, by this time, acquired patches of green algae and forms
of mosses and liverworts were growing at the edge of bodies of water.
- Segmented animals from the sea (ancestors of the millipedes) began
feeding on this source of food.
- The first fossils of arachnids (spiders) and centipedes are found
in the Silurian.
- At the end of the Devonian period the first land vertebrates
appeared. The freshwater fish are thought to have developed a flotation bladder with a
dense network of blood vessels that allowed a large gas exchange area to ensure an
adequate supply of oxygen for survival when oxygen supplies in the water were low.
Lungfish evolved from these fish.
- These lungfish were able to survive in a terrestrial environment as
they now had the means to breathe without water and their physical characteristics of
tough scaly skin, rudimentary limbs and powerful muscles equipped them for living on land
as well as in the water. However, the lungfish skeleton was made partly of cartilage and
so was unable to support them for long periods on land.
- At the end of the Devonian and the beginning of the Carboniferous
the amphibians emerged. With the evolution of an air passage from the nostrils to the roof
of the mouth the first amphibians took to the land.
- The freshwater fish that gave rise to the amphibians are thought to have resembled today's lungfish.
summarise
the main evolutionary changes resulting from the selection of living things exhibiting
features that allowed them to survive in terrestrial environments
Organisms need certain environmental conditions to survive in any environment. In a new environment, there may be conditions that will make it hard for organisms to survive. Only if these environmental pressures are overcome will organisms survive.
Features that allow living things to survive in terrestrial environments are:
- Internal watery environment: Desiccation or drying out will occur
if there is not enough available water for organisms. Watery environments are still needed
for reproduction, so vertebrates need a mechanism such as hard or leathery coverings to
stop drying of eggs and developing embryos. Fertilisation of eggs is facilitated in
a watery internal medium. Internal gestation of embryos protects them from desiccation.
- Stronger support structures: In the absence of buoyancy provided by
water, animals and plants evolved structures to support their own weight. Plants developed
roots systems which hold them in the ground, and woody stems which provide support.
Vertebrates developed an internal skeleton which supports body weight and enables
mobility.
- Strategies to manage a greater range of temperature:
The temperature range is much greater on land than in water. Early land
animals would have been cold blooded (poikilothermic) so would need to have
developed behaviours to keep them cooler when the environment was hot and warm
when environmental temperatures dropped. One way would have been to return to
the water temporarily
- New means of obtaining food: In the case of plants, the soil type and atmospheric conditions would be important to ensure a supply of minerals and carbon dioxide for photosynthesis to occur but there would have been plenty of carbon dioxide in the atmosphere. The early land animals would have fed off small invertebrates such as the ancestors of today's millipedes and early arachnids. They appear not to have been herbivorous as it appears they didn't have the gut organisms to break down the cellulose in the plants.
identify the advantages the terrestrial environment offered to the first land plants and animals
The first land-dwellers were able to enjoy the advantage of:
- few predators
- little competition for space
- abundant food supplies.
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