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EOSC 310 > 1.5 Building Blocks and Dating > Flashcards

1.5 Building Blocks and Dating Flashcards

1
Q

WHERE DO MOLECULES BEGIN?

How do we go from the elemental products of nucleosynthesis to the formation of molecules?

A

Molecules begin to form in interstellar clouds (nebulae) shortly after supernovas distribute the elements

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2
Q

WHAT CAN EXIST IN INTERSTELLAR CLOUDS?

How do we go from the elemental products of nucleosynthesis to the formation of molecules?

A

Silicate minerals, which are the most common minerals in Earth’s rocks, are known to exist in these clouds, along with organic molecules

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3
Q

HOW ARE MOLECULES CONSTRUCTED?

How do we go from the elemental products of nucleosynthesis to the formation of molecules?

A

It’s likely that molecules are constructed through processes driven by radiation from stars, although this is not yet fully understood

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4
Q

WHAT’S THE BASIC BUILDING BLOCK OF OUR PLANET?

1.5.1.1 Mineral definition

A

Minerals: “a naturally occurring inorganic element or compound having an orderly internal structure and characteristic chemical composition, crystal form, and physical properties”

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5
Q

WHAT DO MINERALS NOT INCLUDE?

A

As per the geological definition, minerals typically do not include compounds found exclusively in living organisms.

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6
Q

SILICATE MINERALS CONTAIN…

1.5.1.2 Mineral types

A
  • a silicon-oxygen structure called a tetrahedron, SiO4, where four oxygen atoms are bound to 1 silicon atom to form a pyramid-like structure
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7
Q

Silicates can also form three-dimensional structures known as…

A

…framework silicates - characterized by a 3-dimensional network of tetrahedra

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8
Q

Framework silicates include some of the most common minerals in Earth’s continental crust, such as WHAT?

A
  • QUARTZ
  • FELDSPAR
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9
Q

Quartz

Framework silicates include some of the most common minerals in Earth’s continental crust, such as WHAT?

A
  • Quartz is composed entirely of these tetrahedra linked together in a continuous framework
  • Occasionally, impurities can lead to coloured varieties of quartz, such as purple amethyst, which is caused by trace amounts of iron.
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10
Q

Feldspar

Framework silicates include some of the most common minerals in Earth’s continental crust, such as WHAT?

A

Feldspars, another group of framework silicates, contain significant quantities of aluminum, potassium, sodium, and calcium

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11
Q

WHICH IS MORE IMPORTANT OF THE TWO?

Framework silicates include some of the most common minerals in Earth’s continental crust, such as WHAT?

A

Although feldspar is the most common mineral in the crust, quartz is the most abundant mineral on the Earth’s surface due to its durability and resistance to weathering.

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12
Q

Non-silicate materials

A

1) calcite (CaCO₃)
2) halite (NaCl)
3) pyrite (FeS₂—commonly known as fool’s gold) hematite (Fe₂O₃)

Various metals, often called native metals, such as gold, silver, and copper, are also classified as minerals

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13
Q

How and when do minerals form?

A
  • Crystals grow from a small single-molecule structure through a process called nucleation to their final visible form.
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14
Q

How to minerals form a cubic crystal?

A

Separate atoms -> initial nucleation (slight clumping) -> continued growth (larger clumping) -> formation of crystal faces (cubic formation) -> CUBE

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15
Q

What are the principle mechanisms of mineral formation?

A
  1. From Cooling Magma
  2. Precipitating from an aqueous solution
  3. A rock is changed during metamorphism
  4. As a rock is changed during weathering
  5. Biological precipitation
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16
Q

From cooling magma

What are the principle mechanisms of mineral formation?

A

As magma rises through the crust, it cools, and minerals begin to crystallize.

SIZE OF CRYSTAL:
* If magma cools rapidly only small crystals can form before the molten material solidifies into rock: Extrusive
* As such, magma that cools deeper in the crust will have larger crystals than those that cool closer to or are erupted at the surface as lava: AKA intrusive or plutonic

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17
Q

Precipitation from aqueous solution

What are the principle mechanisms of mineral formation?

A

2 ways:

  • When hot fluids saturated with various ions move through the subsurface, minerals can precipitate in cracks, forming veins.
  • Minerals can also form via the evaporation of inland seas or lakes. A notable example is rock salt (halite), which crystallizes as seawater evaporates.
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18
Q

Metamorphism

What are the principle mechanisms of mineral formation?

A
  • Metamorphism is the process by which minerals change in response to increasing temperature and pressure.
  • During this process, new minerals can form from the elements within existing minerals, leading to the creation of more stable forms at these higher temperatures and pressures
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19
Q

Weathering

What are the principle mechanisms of mineral formation?

A
  • Weathering alters minerals that are unstable at the low-pressure, low-temperature conditions at the Earth’s surface, transforming them into more stable forms.
  • This process can be considered a type of metamorphism occurring
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20
Q

Biological precipitation

What are the principle mechanisms of mineral formation?

A
  • Includes: …shells, bones, and teeth
  • Life uses various minerals, including calcite, used by many clams to make shells.
  • Teeth and bones are often made from varieties of the mineral apatite, and some creatures (for example, some types of sponges) secrete silica (quartz) skeletons,
21
Q

How are rocks related to minerals?

1.5.1.4 Rocks

A
  • Rocks are essentially aggregates of minerals
  • Can be composed of multiple minerals; for example, granite is mostly composed of quartz and feldspar (framework silicates)
  • Rocks can also be composed of just one mineral (monomineralic)
22
Q

The rock cycle:

A

…describes the formation, transformation, and recycling of rocks on Earth’s surface and involves the three main types of rocks: igneous, sedimentary, and metamorphic.

23
Q

If magma COOLS and CRYSTALIZES inside the Earth..

The rock cycle

A

it forms an INTRUSIVE igneous rock, such as granite

24
Q

If the magma reaches the surface via a volcano…

The rock cycle

A

…it erupts and cools rapidly forming an EXTRUSIVE igneous rock such as basalt

25
WEATHERING processes then... ## Footnote The rock cycle
break down and **ERODE** extrusive igneous rocks
26
The resulting fragments are... ## Footnote The rock cycle
TRANSPORTED and then DEPOSITED as **sediments**
27
As the sediments are BURIED over time, ## Footnote The rock cycle
compaction and cementation may convert them into **sedimentary rocks**, such as sandstone, shale, or limestone - together the processes that convert sediment to rock are referred to as **DIAGENSIS**
28
If the sedimentary rocks are BURIED DEEPER... ## Footnote The rock cycle
...heat, pressure, and chemical processes may **METAMORPHOSE** (transform) them into metamorphic rocks
29
If temperatures become high enough, these metamorphic rocks may start to MELT… ## Footnote The rock cycle
… potentially generating new MAGMA
30
Certain minerals that contain radioactive materials can also be used as… ## Footnote 1.5.2: Dating rocks with materials
* **TIME PIECES**; provide dates for geological materials and help us place specific dates on the geological time scale * **HOW DO WE DO THIS?** Radiometric dating
31
Alpha Decay ## Footnote 1.5.2.1 Radioactive decay
* **Two protons and two neutrons** (essentially helium nuclei) **are released**. * This process *decreases* the atomic mass number (A) by 4 and the atomic number (Z) by 2
32
Beta Decay ## Footnote 1.5.2.1 Radioactive decay
* A **beta** particle (an **electron**) **is released**, and a neutron is converted into a proton. * The atomic mass number (A) remains *unchanged*, while the atomic number (Z) *increases* by 1 (Figure 13, middle).
33
Gamma Decay ## Footnote 1.5.2.1 Radioactive decay
* A gamma ray (photon) is emitted. * **No particles are ejected**, so both the atomic mass number (A) and the atomic number (Z) remain unchanged (Figure 13, bottom).
34
How does decay continue?
the original radioactive isotope (called the parent) is transformed through unstable intermediary isotopes until a stable (daughter) element forms, and decay stops.
35
How are radioactive isotopes trapped for radiometric dating?
* As magma cools, crystals form, trapping radioactive isotopes within them. * These crystals in igneous rocks often act as closed systems, preventing the entry or exit of materials once they have formed (LIKE A BARRIER)
36
How are stable daughter products made?
* As the parent isotope decays within the magma crystal, **it produces stable daughter products**. * Since the crystals function as closed systems, the proportion of parent-to-daughter isotopes at any given time can indicate when the mineral crystallized from the magma.
37
The decay of the parent to a stable daughter is expressed in… ## Footnote DECAY FROM PARENT -> DAUGHTER:
* …**half-lives** - the time it takes for ***half*** of the parent to decay into a stable daughter * Different systems have different half-lives, use different source materials for dating and may be more or less useful depending on what rocks you are trying to date
38
At what point are half-lives too little (amount-wise)?
**After about *ten* half-lives**, there is often too little parent remaining to detect.
39
If possible, multiple systems are used to cross-check any dates produced, INCLUDING:
* Uranium lead systems
40
Uranium lead systems - WHY?
Dating younger rocks can be challenging due to the difficulty in detecting the daughter isotopes.
41
Uranium lead systems - most common mineral:
Zircon (ZrSiO₄) - has several advantages for radiometric dating: 1. **Abundance**: Zircon is a common mineral in igneous rocks. 2. **Durability**: It is hard and resistant to weathering, which minimizes the risk of leakage of parent or daughter isotopes. 3. **Stability**: Zircon withstands high temperatures and pressures in the Earth’s subsurface, preserving its closed system. 4. **Exclusion of Lead**: During its formation, zircon excludes lead from its crystal structure (Figure 17). As a result, any lead detected in zircon must be a product of radioactive decay.
42
3 Limitations
* 1. Sedimentary Rocks * 2. Weathering * 3. Metamorphism
43
Sedimentary Rocks ## Footnote 3 Limitations
* Even if minerals like zircons are found in clastic sedimentary rocks (composed of fragments from other rocks), **those zircons are remnants of pre-existing igneous or metamorphic rocks** * Consequently, the zircons would provide the age of the original igneous or metamorphic rock rather than the age of sediment deposition. * This is a significant limitation because sedimentary rocks make up about 75% of Earth’s rocks
44
2. Weathering ## Footnote 3 Limitations
Weathering can affect igneous or metamorphic rocks by leaching out isotopes from minerals, which can compromise the closed system necessary for accurate radiometric dating
45
3. Metamorphism ## Footnote 3 Limitations
* During metamorphism, rocks are subjected to high temperatures and pressures, which can cause isotopes to leak out of minerals. * This is related to the concept of closure
46
Metamorphism - closure ## Footnote 3 Limitations
* Closure: the temperature below which a mineral becomes a closed system that prevents the leakage of daughter products, or above which daughter products may start to escape from the crystal * The longer a mineral is heated above its closure temperature, the more daughter product it may lose. If only a proportion of daughter products are lost, it can make the crystal appear younger than its true age. * If all daughter products are lost, the radiometric clock is effectively reset to zero.
47
Stratigraphic usefulness - Stratigraphy:
* Stratigraphy describes how rock layers (strata) are arranged through time. * While sedimentary rocks in strata cannot be dated directly using radiometric techniques, igneous rocks can help bracket certain parts of a sequence.
48
Volcanic ash deposits can be very beneficial when dating sedimentary sequences - HOW? ## Footnote Stratigraphic usefulness
* Ash forms when magma rapidly depressurizes during an eruption. * This **depressurization** causes bubbles in the magma to expand quickly, fragmenting the magma and ejecting it violently from the volcano * Along with the rapidly cooled magma, which forms volcanic glass and constitutes most of the ash cloud, **zircon crystals that were forming just before the eruption are also ejected.** * Ash and zircons can travel hundreds or even thousands of kilometres, settling as a layer on the Earth’s surface. * **Successive eruptions can create multiple ash layers in sedimentary sequences, which can be dated using the resilient zircons they contain**

EOSC 310 (23 decks)

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