Mystery Mix
Why might there be a horizontal gap (uniformity) in the layers of sedimentary rock?
Because of weathering and erosion. Over a very long period of time, water flowing across the surface of the rock can break the rock down into sediment and carry it away, leaving a gap.
What is the law of cross cutting relationships
A rock feature that cuts across another rock feature is the younger of the two features.
Usually refers to a Fault or an intrusion.
What is older a fossil with 90% of its Carbon-14 atoms remaining or a fossil with 60% of its Carbon-14 atoms remaining.
The fossil with 60% of its Carbon-14 atoms is older.
Remember you will have 100% Carbon if you are alive.
According to the law of cross cutting relationships, the feature that cuts through the layers are younger. So, the fault would be younger.
What is the preserved remains of an organism called?
A fossil
What type of dating uses radioactive elements to date fossils and rocks?
Absolute Dating
What is the principle of original horizontality
rock layers form when sediments are deposited in horizontal layers due to gravity.Scientists use this principle to help them date geologic events.
What does Carbon Decay into?
Nitrogen
What is an intrusion?
When magma pushes, or intrudes, into these cracks or areas of weakness, it causes them to widen. Over time the magma cools and solidifies to form new igneous rock called an intrusion.
Which law states that the sequence of changes in organisms as recorded by fossils is the same everywhere on Earth.
The law of fossil succession.
If you have the same fossils you have the same rock layers and therefore they are the same age.
This type of dating uses a lab, chemistry, and igneous rocks.
Absolute Dating
What is the law of fossil succession
The changes that any type of organism goes through occur in the same order everywhere you find fossils of that organism. So, if you find the same kinds of fossils in rock strata from different locations, you can assume that the rock strata are the same age.
What does Uranium decay into?
Lead
Can you apply the law of cross cutting relationships to faults?
Yes, like an igneous intrusion, a fault is younger than the rock it cuts across.
Which kind of fossils are more useful for relative dating?
Index fossils which are which are fossils of organisms that lived over a widespread area for a short period of geologic time and so can be used to date the rock layers in which they occur.
How is volcano strata dated?
To date volcanic rock, a sample may be crushed into a fine powder so that it can be chemically analyzed in a laboratory to find its age. Remember volcanoes produce igneous rock which is crushed in Absolute dating.
What does the Law of Superposition State?
Rock layers that form on top of other layers are younger than the layers below.
Identify the percentages of Uranium-235 as it decays into lead through 3 half lives.
Half life 1 = 50% Uranium to 50% Lead
Half Life 2 = 25% Uranium to 75% Lead
Half Life 3 = 12.5% Uranium to 87.5% Lead
What causes Faults to form and what does it do to the rock layers (strata)?
Earthquakes/tectonic forces can cause a fault to form which produces a crack in the strata (rock layers).
The crack produced can cause the layers to no longer line up. We have to use relative dating techniques to determine which layers are the same.
Why are index fossils used for relative dating?
Because they are widely distributed, easy to identify, and existed for a relatively short amount of geologic time.
Explain the difference between absolute and relative dating?
Relative dating is used to determine the age of a rock layer compared to the layers around it. It gives the sequence in which events occurred in Earth’s history.
Absolute dating is used to determine the age of a rock or event in years.
What is the principle of lateral continuity?
When sediments are deposited to form layers, the layers extend laterally, or horizontally, in all directions until they reach an obstacle.
It takes 700 million years for half of the amount of uranium-235 originally in rock to turn into lead. If a scientist measures that a sample is 6.25% Uranium-235 and 93.75% lead, how old is the sample?
2,800 million years old
Note: Uranium-238 has a half life of 4.5 billion years. This question was in reference to Uranium-235 which has a half life of 700 million years.
Over time the magma cools and solidifies to form new igneous rock called. It can cut through other rock layers. What is this feature called and what law does it represent?
Why are graptolites, ammonites, and foraminifera good index fossils
Because they changed forms and evolved into many new species, relatively quickly. Each of these groups of animals lived in the ocean, which allowed their fossils to be widespread.