Earth System Science VSI

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The Earth has experienced huge changes over very long time frames but feedback induced stability over shorter time frames.
Author

Stephen J. Mildenhall

Published

2024-03-12

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Earth System Science

  • p4 as the sun got brighter (over its life) CO2 decreased enabling the planet to say cold
    • silictate weathering is a big driver of this p9
  • life influences the atmosphere - there’d be no O2 w/o life (so you can get some idea if there is life on a planet from its atmosphere)
  • feedbacks: ice-albedo important
  • recycling is key to long-term stability: O, C, N, P (phosphorous)
  • oxygen [CO2+ H20 + sun –> glucose + O2 = photosynthesis p23]
  • Photosynthesis = 130TW (tera Watts), half on land, half at sea
  • Oxidized = adding electrons; reduced is subtracting electrons
  • 0.1% of organic carbon is recycled, but rest is buried in new sedimentary rocks, leading to extra O2 p24
  • lots more O in earths crust than carbon => must have been a source = loss of H to space (from water)
  • Lots more O than Carbon
  • P, N needed in DNA, APT, cell walls etc. all crucial for life
  • N in atmosphere is very stable, hard to extract
  • p46: silicate weathering and long term CO2 regulation; when forests emerged, accel of silicate weathering lowered conc of atmost CO2 by order of magnitude [Fig 16, p48]
  • p55 Antarctic ice core: bubbles of air measure CO2 directly; isotope ratio measured temp
  • p64: oxygenic photosynthesis is more efficient and important; took longer to evolve; p66 great oxidation; origin of eukaryotes (complex cells)
  • snowball earths
  • p81 human agriculture 50EJ (exa \(10^{18}\) Joules); all human activity 500EJ, energy captured by photosynthesis 5000EJ
  • O2 levels, forests, but not too hot to have fires
  • p97: 500BT carbon is 1C [have burned 400BT and seem 0.8C warming]
  • Human life needs to recycle like nature to be sustainable
  • Ch8 interesting on other planets, habitable zone
  • Younger Dryas
  • Green sahara
  • p128 habitable zone distance from sun

Periodic table: B C N O F Ne / AL SI P S Cl Ar

Spheres

  • bio = all living things and their interactions
  • litho = core and upper mantle
  • hydro = water
  • atmo = gas

GPT Notes

Silicates are a group of minerals that are the most abundant in the Earth’s crust. They are composed of silicon and oxygen, typically with the addition of various metals such as aluminum, magnesium, iron, calcium, and sodium. The basic structural unit of silicates is the silica tetrahedron (\(SiO_4^{4-}\)), where a silicon atom is bonded to four oxygen atoms in a tetrahedral arrangement. These tetrahedra can link together in various ways—by sharing oxygen atoms—to form different silicate structures, such as single tetrahedra, chains, sheets, or three-dimensional frameworks. This structural variety allows for the vast diversity of silicate minerals, including quartz, feldspars, micas, and olivines, each with unique physical and chemical properties. Silicates are crucial to geology, soil science, and various industrial applications, including ceramics, glass, and construction materials.

The upper mantle, part of the Earth’s mantle situated just below the crust and extending to a depth of about 400 kilometers, is composed primarily of silicate minerals. Its composition is thought to be predominantly peridotite, a dense, coarse-grained rock consisting mainly of the minerals olivine and pyroxenes, with smaller amounts of amphibole and mica in some locations.

The approximate proportionate makeup of the upper mantle is as follows:

  • Olivine (\(Mg,Fe)_2SiO_4\): 40-60%
  • Orthopyroxene (\(Mg,Fe)SiO_3\): 15-25%
  • Clinopyroxene (\(Ca(Mg,Fe)Si_2O_6\)): 10-25%
  • Garnet (\(Ca_3Al_2(SiO_4)_3\) in deeper parts or Spinel (\(MgAl_2O_4\)) in shallower parts: 5-15%, depending on depth
  • Minor amounts of amphibole, mica, and aluminum silicates in certain regions

This composition can vary based on depth, temperature, pressure conditions, and the specific location within the mantle. The upper mantle plays a crucial role in plate tectonics and the movement of lithospheric plates, influencing volcanic activity and the formation of mountain ranges.

The composition of the Earth by element, considering both the crust and the entire planet, varies significantly due to the different densities and chemical properties of the layers (crust, mantle, core). Here’s a summary:

Crust

The Earth’s crust is predominantly composed of oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium. The approximate percentage by weight of the most abundant elements in the Earth’s crust is:

  • Oxygen: 46.6%
  • Silicon: 27.7%
  • Aluminum: 8.1%
  • Iron: 5.0%
  • Calcium: 3.6%
  • Sodium: 2.8%
  • Potassium: 2.6%
  • Magnesium: 2.1%
  • Other elements make up the remaining percentage.

Whole Earth

When considering the whole Earth (including the mantle and core), the composition shifts significantly towards heavier elements:

  • Iron: ~32%
  • Oxygen: ~30%
  • Silicon: ~15%
  • Magnesium: ~14%
  • Nickel: ~2%
  • Sulfur: ~1.5%
  • Titanium: ~0.4%
  • Other elements make up the remainder, including calcium, aluminum, and others in smaller amounts.

The core, which constitutes a significant portion of the Earth’s mass, is primarily composed of iron and nickel, making iron the most abundant element in the Earth by mass. The mantle’s composition is more silicate-rich, influencing the overall elemental distribution.

Here is a simplified table presenting the distribution of carbon on Earth across different reservoirs, expressed as approximate percentages of the total carbon:

Reservoir Carbon (GtC) Percentage of Total Carbon
Deep Earth (Mantle and Crust) Thousands to tens of thousands of GtC Majority
Oceans ~38,000 Significant but smaller than solid Earth
Atmosphere ~750 < 1%
Terrestrial Biosphere (living things, detritus, soil) ~2,000 < 1%
Fossil Fuels ~4,000 < 1% (but significant for climate change)
Sediments and Sedimentary Rocks 60,000,000 to 100,000,000 > 90% (largest reservoir)

Note: The “Percentage of Total Carbon” is a rough approximation due to the significant uncertainties, especially in estimating the carbon in the deep Earth. The vast majority of Earth’s carbon is stored in sediments and sedimentary rocks, followed by the mantle, making these the dominant reservoirs.

Phosphorus is essential to life for several key reasons:

  1. Structural Component of Nucleic Acids: Phosphorus is a critical element in the backbone of DNA and RNA, the molecules responsible for storing and transmitting genetic information in all living organisms.

  2. Energy Storage and Transfer: Phosphorus is a part of adenosine triphosphate (ATP), the primary energy carrier in cells. ATP molecules release energy when they are broken down, which is used for various cellular processes.

  3. Cell Membrane Structure: Phosphorus is found in phospholipids, which are the primary components of cell membranes. These membranes enclose cells and their internal components, playing a crucial role in protecting cells and regulating the movement of substances in and out of cells.

  4. Bone and Teeth Formation: In vertebrates, phosphorus, in the form of phosphate, combines with calcium to form hydroxyapatite, which provides strength and structure to bones and teeth.

  5. Biochemical Pathways: Phosphorus is involved in numerous biochemical pathways, including those related to the metabolism of proteins, carbohydrates, and fats. It is also crucial for the regulation of pH in the body and the activation and deactivation of enzymes.

Due to its vital roles in energy transfer, genetic material, structural components of cells, and skeletal structure, phosphorus is indispensable to the growth, maintenance, and repair of all tissues and cells in living organisms.

Nitrogen is another crucial element for life, integral to many biological processes and structures:

  1. Proteins: Nitrogen is a fundamental component of amino acids, the building blocks of proteins. Proteins perform a wide range of functions in living organisms, including acting as enzymes, structural components, and signaling molecules.

  2. Nucleic Acids: Nitrogen is present in the bases that make up DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), which are essential for genetic information storage, transfer, and the synthesis of proteins.

  3. Energy Metabolism: Some forms of nitrogen are involved in energy transfer within cells, such as in the form of adenosine triphosphate (ATP) and other nucleotides.

  4. Chlorophyll: Nitrogen is a component of chlorophyll, the molecule that plants and algae use to capture light energy during photosynthesis, converting it into chemical energy.

  5. Biochemical Reactions: Nitrogen is a key part of many enzymes and coenzymes, which catalyze biochemical reactions necessary for metabolism and other cellular functions.

The nitrogen cycle is essential for converting atmospheric nitrogen (\(N_2\)), which makes up about 78% of the Earth’s atmosphere and is inert, into forms that are biologically available to organisms (such as ammonia, nitrate, and nitrite). This conversion is crucial because most organisms cannot use atmospheric nitrogen directly. Nitrogen-fixing bacteria, nitrification, and denitrification processes transform nitrogen into various compounds that are utilized by plants and, subsequently, by animals and decomposers, making nitrogen a vital element in ecosystems and agriculture.

Silicate rock weathering is a fundamental geological process that involves the breakdown and alteration of silicate minerals in rocks when they are exposed to the atmosphere, moisture, and biological activity. This process plays a crucial role in the Earth’s carbon cycle and has a significant impact on climate over geological timescales. There are several key aspects to consider:

Chemical Weathering

Chemical weathering of silicate rocks involves the reaction of mineral surfaces with water, carbon dioxide (CO2), and other acidic compounds in the environment, leading to the dissolution of minerals and the formation of new minerals, such as clay, and soluble ions. One important reaction is the carbonation process, where CO2 dissolved in rainwater forms carbonic acid, which then reacts with silicate minerals. This reaction can lead to the removal of CO2 from the atmosphere and its eventual storage in the ocean or soil as carbonate minerals or bicarbonate ions.

Physical Weathering

Physical or mechanical weathering breaks down rocks into smaller pieces without changing their chemical composition. This can occur through freeze-thaw cycles, thermal expansion, root growth, and other physical forces. Physical weathering increases the surface area of rock available for chemical weathering.

Biological Weathering

Organisms, including plants, fungi, and bacteria, can also contribute to the weathering of silicate rocks. For example, plant roots can penetrate and physically break rock, while the organic acids produced by roots and microorganisms can chemically alter minerals.

Implications for the Carbon Cycle

Silicate rock weathering is a critical component of the long-term carbon cycle. By converting atmospheric CO2 into bicarbonate ions that are carried to the oceans and eventually precipitated as carbonate minerals on the seafloor, weathering acts as a natural regulator of atmospheric CO2 levels over millions of years. This process influences global climate by controlling the greenhouse gas concentration in the atmosphere.

Rate Factors

The rate of silicate weathering is influenced by several factors, including temperature, rainfall, the presence of soil and vegetation, and the mineral composition of the rocks themselves. Warmer, wetter climates typically enhance weathering rates.

Silicate rock weathering is a slow but steady process that shapes landscapes, influences the global carbon cycle, and regulates the Earth’s climate over geologic time scales.

Deets

  • Tim Lenton
  • Volume 464
  • Published 2016