Other Evidence of Evolution - Chapter 11 Flashcards
Fossil
evidence of, or remains of, an organism that lived long ago.
Types of soil and fossilisation
wet acidic soils - minerals in bone are dissolved and no fossilisation occurs
alkaline soils - produce the best fossils because the minerals in the bones are not dissolved
Where are fossils often found?
edges of ancient lakes and river systems, in caves or in volcanically active areas. this is because the organism can be buried rapidly, preventing decomposition.
lakes/rivers - sediments
caves - limestone (consists of calcium carbonate)
Discovery of fossils
fossils discovered by excavations:
- first the area is surveyed and marked out in sections
- small hand tools are used to remove the soil gently
- soil that has been removed is usually sieved so that small fragments are not overlooked
Artefacts
an object made or modified by humans.
Dating
determining the age of excavated artefacts or fossils.
Absolute dates
the actual age of a specimen in years
Relative dates
a comparison of fossils to tell us whether one sample is older or younger than another.
Potassium-argon dating
A method of calculating the age of a fossil or artefact using the known rate of decay of radioactive potassium.
Potassium is a mixture of 3 different isotopes:
1. Potassium-39 have 20 neutrons
2. Potassium-40 have 21 neutrons – radioactive isotope and decays from calcium-40 and argon-40. This decay is a slow process and the determination of the amounts of potassium-40 and argon-40 in rock samples allows calculation of age of rock. With age, potassium-40 decreases and argon-40 increases.
3. Potassium-41 have 22 neutrons
Limited usefulness: not all rock types are suitable for this method of dating and it can only date rocks older than 100 000 - 200 000 years.
Half-life
the time required for half of any quantity of radioactive material to decay into stable, non-radioactive material.
- Half-life of potassium-40 is 1250 billion years.
Carbon-14 dating
Based on the decay of the radioactive isotope of carbon, carbon-14 to nitrogen.
- Carbon-14 produced in upper atmosphere
- There is a ratio of one carbon-14 atom to every million million atoms of the stable isotope carbon-12
- Animals’ intake carbon-14 from plants which take it from the atmosphere
- When death occurs, intake of C-14 ceases.
- C-14 in the tissues decays at a fixed rate
- Measuring the amount of radiation liberated by a sample, ratio of C-12 to C-14 can be measured.
- From this an age can be calculated
Accelerator mass spectrometry (AMS)
a technique used to give radiocarbon dates for very small samples of material (100 micrograms)
- involves breaking the sample up into its constituent atoms so that the number of atoms for each isotope of carbon can be counted
- possible to date cave paintings from pigments
- material in pigments must be organic compounds and include charcoal, honey, milk, blood or oil seed
- cannot be used to date back more than about 60 000 years
Stratigraphy
the study of the sequence of rock layers as a means of relative dating. includes:
- principle of superposition
- correlation of rock strata
- index fossils
Principle of superposition
assumes that in layers of sedimentary rock, the layers at the top are younger than those beneath them. (fossils and other material found at the top are younger)
Correlation of rock strata
involves matching rock strata from different areas. matching can be done by examining the rock itself and also studying the fossils it contains.
Index fossils
are fossils or organisms that are widely distributed and present on earth for only a short period of time - useful in relative dating of data, making it more precise.
Requirements for fossils to form:
- a quick burial of the material
- the presence of hard body parts
- an absence of decay organisms
- a long period of stability - the organism needs to be left undisturbed
5 Problems with the fossil record:
- fossils are hard to form - certain conditions must be fulfilled for fossilisation to occur.
- fossils are hard to find - some are buried too deep underground or are inaccessible.
- fossils are hard to classify - they may not have been recognised as fossils and been discarded.
- fossils are hard to preserve - fossils have been destroyed by the earths crust movement or human activity.
- fossils are hard to date - in order to place the fossils on the fossil record, the age of the fossil must be determined.
Embryology
definition - comparing the very early stages of the development of organisms
- in vertebrates, comparing embryonic stages reveals remarkable similarity between different species at different times
- embryos of humans and chickens have slits and arches in their necks. these similarities reveal a common ancestor
- features common to vertebrate embryos include a tail. two chambered heart and similar brain development.
Homologous structures
definition - structures that are similar in structure but may be used in different ways.
- forelimbs of vertebrates possess similar structures - feet of amphibians and reptiles - wings of bats and birds - leg of a horse - flipper of a whale/seal - human hand
- organisms possessing homologous structures are likely to have a common ancestor
Vestigial structures
definition - structures that have changed during evolution to the point that they no longer fulfil their origin function.
- natural selection has reduced the organs to non-functional remnants as it would have been a waste of the organisms energy and resources to maintain useless structures.
Examples of vestigial structures
- nictitating membrane
- external ear muscles
- third molars
- pyramidalis muscles
- tail
- male nipples
- muscles at base of hairs
- appendix
