Human Bio Ch 11 Flashcards
What is a fossil?
Evidence of, or remains of, an organism that lived long ago.
Some fossils are bones, shells or teeth. They do not have to be apart of the organism they can also be, footprints, burrows, faeces or impressions.
What are the conditions for fossil formation?
Parts of organisms may be fossilised when buried by drifting sand, mud deposited by rivers or volcanic ash.
The effect of soil type varies. When wet and acidic the minerals in the bone are dissolved and no fossilisation can occur. Soil that contains no oxygen can preserve organisms.
Alkaline soils produce the best fossils because the minerals in the bones are not dissolved, lime or iron oxide go into the pores of the body and make up about 35% of the weight of the bone. The bones become petrified (turn into rock) without losing its structure.
What are the main locations of fossils?
Edges of ancient lakes and river systems
Caves
Volcanically active areas.
This is because the organism can be buried rapidly, preventing decomposition.
How are fossils discovered?
Fossils are sometimes found by chance at the surface of the ground where they may have been uncovered by erosion, but more often the discovery of fossils is the result of slow and painstaking excavation of likely sites.
Small hand tools are used to remove the soil gently so as not the damage any of the material. The soil removed is usually sieved so that even very small fragments are not overlooked.
What is an artefact?
An object made or modified by humans.
What is dating in terms of fossils and what are the 2 types?
Determining the age of excavated artefacts or fossils.
2 types:
1. Absolute dating - the actual age in years of a fossil or artefact.
2. Relative dating - the age of a fossil or artefact relative to another fossil or artefact (whether older or younger).
Modern technology has enabled accurate estimates to be made of the absolute age of many samples, however when that is not possible knowing whether one fossil is older or younger than another is very important.
What are the 2 names of absolute dating?
- Potassium - argon dating
- Carbon - 14 dating
What is potassium argon dating and what is its process?
A method of calculating the age of a fossil or artefact using the known rate of decay or radioactive potassium.
Potassium-40 is a radioactive isotope that decays to form calcium-40 and argon-40. Such decay takes place at an extremely slow but constant rate, and so determining the amounts of potassium-40 and argon-40 in a rock sample enable the age of the rock to be calculated. As the rock ages the proportion of potassium-40 decreases whilst argon-40 increases.
The limitations include, not all rock types are suitable for this method of dating and it can only date rocks older that 100,000 years.
The half-life (time required for just half of the radioactive material to decay into non-radioactive material) is 1250 billion years. This means its takes 1250 billion years for just half of the potassium-40 to decay.
What is carbon-14 dating and what is its process?
The calculation of the age of a fossil or artefact using the known rate of decay of radioactive carbon.
Carbon-14 is produced in the upper atmosphere by the action of cosmic radiation on nitrogen at about the same rate at which it decays.
When green plants use atmospheric carbon dioxide during photosynthesis a small amount of carbon-14 is then incorporated into the plant tissue. Should animals eat these plants, the carbon-14 then becomes apart of the animals tissue. With death an organism continues to decay at a fixed rate. By measuring the amount of radiation liberated by a sample, the ration of carbon-14 to carbon-12 can be estimated and from this the age of the sample can be determined.
The rate of decay of carbon-14 to nitrogen has a half life of 5730 years. This method cannot be used to date fossils older than 60,000 years as the percentage of carbon-14 left is so small, the fossils also must contain organic compounds, compounds from living things that contain carbon.
What is the relative dating method known as stratigraphy and what is its process?
The study of layers or stratas and the sequence of rock layers as a means of relative dating.
The first use of stratigraphy is the principle of superposition which assumes that in layers of sedimentary rock the layers at the top are younger than the ones beneath them. This principle must be applied with care because distortions of the earth’s crust do occur.
The second use of stratigraphy is in the correlation of rock strata, which involves matching layers of rock from different areas. Matching of strata can be done by examining the rock itself and also by studying the rocks it contains. Rocks that contain the same fossils may be assumed to be of the same age.
Index fossils (fossils or organisms that were on Earth for only a short period of time and are therefore useful in relative dating of rock strata). They are of great value as they are widely distributed and were only on earth for a small period of time, this makes the relative dating of strata more precise.
What are the main problems with the fossil record?
The fossil record is very incomplete as conditions for fossilisation do not always occur or they occur as irregular periods time. For fossils to be formed, 4 main conditions need to be met:
- a quick burial of material
- the presence of hard body parts
- an absence of decay organisms
- a long period of stability - organism needs to be left undisturbed.
What is embryology?
The study of the early development of organisms, in humans from fertilisation to the end of the 8th week of pregnancy.
This showed that both a human embryo and a chicken embryo had slits that were homologous to fish gills.
What are homologous structures?
Structures with a similar structure but not necessarily a similar function.
The most obvious example of homologous structures is the anatomy of forelimbs of vertebrates. The bones are arranged in a very similar way, even though some have developed different functions. This similarity shows that there was likely a common ancestor.
What are vestigial structures?
A structure of reduced size that appears to have no function.
Examples include:
- nictitating membrane (in animals covers the eye for protection in human pinkish membrane in the corner of the eye)
- wisdom teeth
- tails have become coccyx
- male nipples
- the appendix
- muscles that move the ears.
What is a phylogenetic tree?
A diagram showing evolutionary relationships between related organisms. The ancestral organisms form the base of the tree and those organisms that have arisen from it are placed on the end of branches.
identify species with the most common similarities
identify species with next most common similarities
identify which out of the two branched above the next species is most similar to
an axis is drawn to show progress of time.
