Eras are divided into smaller segments called periods. Periods are further divided into epochs.
What is a fossil?
Any evidence of earlier life preserved in a rock.
Identify 2 ways in which original remains are preserved.
(1) the actual unchanged remains of the plant or animal are preserved; (2) more often the soft tissues of an animal decay and disappear , leaving only the original hard parts.
Describe how fossils are preserved as replaced remains and give example of replaced remains.
The soft parts of the original animal have disappeared and the hard parts have been replaced by mineral material. The result is an exact copy of the original plant or animal. Petrified wood is a good example.
How are fossils preserved through molds and casts?
Sometimes a fossil shell or bone completely dissolves out of the rock it was preserved in. This leaves a depression in the rock called a mold. When new material fills that mold it is called a cast.
Give some examples of fossil impressions.
Any impression left in the rock by an animal such as trails, footprints, tracks, burrows, or borings.
What is evolution?
The process of change that produces new life forms over geologic time.
How does the fossil record provide evidence for evolution?
The fossil record shows that through time many kinds of organisms disappear and are replaced by new and different organisms.
What did Charles Darwin mean by natural selection?
Organisms that survive to produce offspring are those who inherited the most beneficial traits for surviving in a particular environment. (Organisms that survived adapted to their environment and passed this on to their offspring)
Compare the rate at which Charles Darwin thought evolution occurred with the rate at which some scientists of today think it occurred.
Darwin concluded that life forms evolve gradually over many generations. Modern scientists believe organism survive for a long time unchanged, then “suddenly” a whole new but related set of organisms appeared, these last a long time, then again a whole new set appear. There is debate about whether evolution follows a gradual path or a path interrupted by short periods of dramatic change.
List the 3 characteristics of the index fossil.
(1) a good index fossil must be easily recognizable; (2) it must be widespread in occurrence; (3) they are limited in time.
What is a key bed? Identify a material that forms good key beds.
A single rock layer that has the same characteristics as a index fossil.
The matching of rock layers from one area to another.
List some methods by which rock layers are correlated.
(1)”walking an outcrop” ; (2) rocks are matched by characteristics like appearance, colour, or composition.
How are fossils indicators of past climates?
For example, coral today is only found in shallow, warm water. When a rock containing fossil coral is found, it can be assumed that the particular area was once an area of shallow warm water.
How are fossils used in oil explorations?
In drilling for oil, long cores of sedimentary rock are obtained and it microfossils are used to compare against cores taken in other locations
Name an describe 3 types of radiation given off be radioactive elements.
alpha, beta and gamma
What is the stable end product from the decay of thorium-234?
The rate at which a radioactive element decays
Describe the radioactive decay of 16 grams of thorium-234.
Thorium-234 has a half-life of 24 days. After 24 days 8 grams will be left. After another 24 days, 4 grams will be left. After another 24 days, 2 grams will be left.... and so on
What is the half-life of radiocarbon?
Which carbon isotope is used for radiocarbon dating and how does it work?
Carbon-14. It decreases at a rate of its half-life (5700 years). By measuring the remaining Carbon-14 we can determine how long ago a plant or animal died and therefore when it lived.
On what kinds of materials can radiocarbon dating be used?
Plants and animals
Identify 2 problems in using radiocarbon dating.
Cannot be used on rocks only plants and animals. The half life of carbon-14 is short so we cannot date back too far.
What are the disadvantages of the uranium-lead method for measuring geologic time?
It is not found in all rocks. Its half life is so long it cannot be used to to tell the age of rocks less than about 10 million years old.
What is the advantage of the rubidium-strontium method?
Can be used to date almost all igneous rocks
What is the advantage of the potassium-argon method?
Can be used to date metamorphic and sedimentary rocks in addition to igneous rocks.
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