Carbon Cycle Requirements for Advanced Life, Part 2
When humans experience or learn of an earthquake or volcano anywhere in the world, a natural response is to express concern and then mobilize to help the suffering. Because these disasters often result in tragedy, many people are surprised to learn that the processes involved in plate tectonics also play a crucial role in sustaining life on Earth. For example, who would have thought that the exchange of carbon between Earth’s layers must occur at just-right rates to ensure our survival? Thanks to ongoing research, scientists have discovered that 60 components of Earth’s deep carbon cycle must be fine-tuned for advanced life.
In part 1 of this two-part series, I described why carbon cycles are crucial for the long-term existence of life on a planet and especially crucial for advanced life. I explained the operation of the different components comprising the shallow carbon cycle. Here in part 2 I will describe the operation of the components of the deep carbon cycle and discuss how our increasing understanding of both the shallow and deep carbon cycles is giving humanity increasing evidences for the existence and operations of God.
Deep Carbon Cycle
Only recently have geophysicists and geochemists gained a good qualitative understanding of the deep carbon cycle. Their capacity to determine the quantities of carbon being moved through the different elements of the deep carbon cycle is just now gaining a measure of confidence. The deep carbon cycle refers to the movements of carbon occurring in the deepest parts of Earth’s crust and throughout the entirety of Earth’s mantle. Earth’s mantle is Earth’s thickest layer. It extends from 5–70 kilometers below Earth’s surface, down to 2,890 kilometers (1,800 miles).
Every year, many megatons of carbon are driven from Earth’s surface and crust into Earth’s mantle through tectonic plate subduction. Earth’s crust is divided into a few dozen tectonic plates. Currently, Earth possesses 10 tectonic plates measuring in excess of 10,000,000 square kilometers, 13 tectonic plates measuring between 1–10 million square kilometers, and 57 microplates measuring less than 1 million square kilometers.1 Tectonic plate subduction occurs when one tectonic plate slides under another and is thereby driven into Earth’s mantle (see figure).
Figure: Tectonic Plate Subduction
On Earth, the collision of an oceanic crustal plate with a continental crustal plate typically results in the oceanic crustal plate sliding underneath the continental crustal plate into Earth’s mantle. Image credit: Subduction-en.svg from Wikimedia Commons by K. D. Schroeder, CC-BY-SA 4.0.
Volcanoes return megatons of carbon trapped in Earth’s mantle back to Earth’s atmosphere and hydrosphere (Earth’s oceans, seas, lakes, rivers, icefields, and glaciers). Whereas the removal of carbon from the atmosphere and hydrosphere through tectonic plate subduction has occurred continuously during the past three billion years, the release of carbon back to the atmosphere through volcanoes occurs episodically. Nevertheless, volcanic eruptions on Earth are neither too frequent nor too seldom, neither too violent nor too tepid, to present a problem either for compensating for the Sun’s increasing luminosity or brightness (see figure in part 1 of this two-part series) or for the long-term survival of life on Earth.
Deep Carbon Cycle’s Fine-Tuned Components and Parameters
There are 23 known subcomponents comprising the deep carbon cycle:
- Oxidation and methanogenesis by microbes residing in the deepest sediments of Earth’s crust2
- Rivers delivering high fluxes of carbon-bearing sediments from continental regions of active tectonic uplift and erosion along deep-sea fans to subduction zones3
- Collisions between continental plates delivering organic carbon via deep-sea fans to subduction zones4
- Sinking of dense mantle material by cold downwellings into isolated thermochemical piles5
- Harsh oxic oceanic sediments that limit biological survivability and productivity near some subduction zones6
- Population growth and spread of carbonate-shell-producing marine microorganisms and bottom-dwelling coccolithophores and foraminifera7
- Subducting tectonic plates that drive two different kinds of chemical reactions: one that returns carbon to the atmosphere, the second that drives carbon into the deep mantle8
- Arc volcanoes that bring the carbon that escapes deep descent through plate subduction to Earth’s surface9
- Volcanic calderas and tectonic faults diffusely emitting carbon dioxide10
- Chemical reactions and movements in tectonic subduction zones that mobilize subducted carbon into fluids and melts11
- Weathering of seafloor basalts that results in the carbonation of these basalts12
- Subduction of carbonated oceanic lithosphere (crustal plates) into the mantle13
- Mantle convection, which is determined by mantle temperature and viscosity, which is determined by the quantity of long-half-life radioisotopes in Earth’s core and mantle and the composition and the compositional heterogeneity of the mantle14
- Mantle cooling rate with respect to mantle depth and mantle density15
- Decompression melting of carbonated mantle material16
- Redox melting of diamond-bearing and metal-carbide-bearing material that is dredged up from the deep mantle to the shallow mantle via large mantle plumes17
- In regions of the mantle that are oxygen-poor, conversion of carbon subducted into the mantle into graphite and diamonds18
- Iron in mantle silicates reacting with graphite to produce carbonate-rich melts19
- Chemical reactions that convert mantle carbon into virtually permanent carbon storage as metal carbides and metal alloys in Earth’s deep mantle20
- Deep faulting and fracturing of oceanic plates, bringing seawater into contact with mantle peridotite, allowing the seawater to chemically react with the mantle peridotite so as to hydrate and carbonate the mantle peridotite, transforming it into serpentinite21
- Subtraction of carbon from subducting slabs via mechanical removal,22 metamorphic decarbonation,23 and melting24
- Magmas dissolving carbon as carbonate in the mantle25
- Vapor-saturated magmas degassing throughout their ascent into the crust26
There are 37 known sets of parameters that affect the rates at which these 23 subcomponents operate:
- Masses of water, nitrogen, and carbon dioxide in Earth’s atmosphere and hydrosphere27
- Population levels and geographical locations of methanogenic and photosynthetic microorganisms28
- Rates at which deep storage petrology occurs29
- Degree of iron-metal saturation in the deep mantle30
- Degree of decompression melting of carbonated mantle material31
- Degree of mantle hydration32
- Degree of mantle viscosity33
- Measure of mantle pressure with respect to mantle depth34
- Measure of redox melting with respect to mantle depth35
- Rates at which basalt is added to the oceanic crust at spreading locations (currently 21 km3 per year) throughout Earth’s history36
- Hydrostatic pressure at the seafloor, which determines the content of carbon dioxide in seafloor water and in seafloor basalts37
- Rates of magma volume expelled from arc volcanoes throughout Earth’s history (currently 0.5 km3 per year)38
- Rates of magma volumes expelled from mantle plume volcanoes (currently 0.4 km3 per year) throughout Earth’s history39
- Heat flow rates in the mantle throughout Earth’s history40
- Quantities of sulfates in the lower crust in the different mantle layers41
- Hydrostatic pressure on the seafloor sediments, which determines the amount of carbon dioxide in deep seawaters and the amount of carbon that can be sequestered in the seafloor sediments42
- Carbonate storage times in ocean crust along passive margins43
- Seep rates associated with gas hydrates in the deep crust and shallow mantle44
- Rates at which serpentinization of mantle minerals occur, which is partly determined by the fracturing extents and rates of oceanic tectonic plates45
- Timing of the onsets in Earth’s history of magmatism, embryonic plate tectonics, and subduction plate tectonics46
- Delivery rates of carbon to Earth from comets, asteroids, and interplanetary dust throughout Earth’s history47
- Oxidation state of the upper mantle throughout Earth’s history48
- Recycling efficiency of carbon relative to water and nitrogen49
- Convergence speed of subducting tectonic plates50
- Fraction of carbon in the oceans that enters deep seafloor subduction zones51
- Rates at which oceanic plates are deeply fractured throughout Earth’s history52
- Seafloor water temperatures throughout Earth’s history53
- Rates at which new organic matter is being produced and delivered into the oceans throughout Earth’s history54
- Timing of the first appearance of calcifying marine microorganisms and of molluscs55
- Ocean pH throughout Earth’s history56
- Ocean salinity throughout Earth’s history57
- Fraction of Earth’s oceans deeper than 3,000 meters throughout Earth’s history58
- Oxygenation level of Earth’s oceans throughout Earth’s history59
- Rate at which the mantle becomes chemically reducing with depth60
- Lengths of Earth’s subduction zones throughout Earth’s history61
- Average oceanic plate thickness throughout Earth’s history62
- Plate tectonic heat transport throughout Earth’s history63
Extraordinary Fine-Tuning Points to Design
The 23 subcomponents of the deep carbon cycle and the 37 parameters that affect the rates at which these 23 subcomponents operate must all be individually fine-tuned so that, in combination with the shallow carbon cycle, carbon dioxide and methane are removed from the atmosphere at just-right rates throughout the 3.8-billion-year history of life Earth in a manner that perfectly and continuously compensates for the Sun’s increasing luminosity (see figure in part 1 of this two-part series). It is the net removal of carbon dioxide and methane that is referred to here. Measurements of the amounts of carbon delivered from Earth’s mantle and crust to Earth’s atmosphere almost, but not quite, equal the amounts of carbon transported from Earth’s atmosphere to Earth’s crust and mantle. It is this slight imbalance that perfectly compensates for the Sun’s increasing luminosity so that life can be sustained and thrive on Earth for 3.8 billion years.
The deep carbon cycle not only plays a crucial role in compensating for the Sun’s increasing luminosity, it also plays a critically essential role in the rise of Earth’s atmospheric oxygen.64 If it were not for organic carbon being efficiently subducted into Earth’s mantle at just-right times in Earth’s history, animal life and human life, in particular, would have been impossible.
Fine-tuning 60 different features and processes on Earth in different ways and at different rates throughout the past 3.8 billion years is no mean task. Even just fine-tuning the features and processes relevant to tectonic plate subduction is a tall order. As geophysicist Robert Stern noted in a paper published in Geology, “Earth is the only known planet with subduction zones and plate tectonics, and this fact demonstrates that special conditions are required for this mode of planetary heat loss.”65 As geophysicist John Hayes and oceanographer Jacob Waldbauer commented in their paper that specifically addressed the subduction components of the deep carbon cycle, “A very clever demon will be required to operate the carbon valve in the subduction zone.”66
However, it takes a lot more than “a clever demon” to explain the exquisite, continual control of the sixty features and processes described here. As the prophet Isaiah in the Bible repeatedly declares,67 only the God that created and designed the universe for humanity’s specific benefit possesses the power, knowledge, intellect, and cleverness to control the natural realm to this extraordinary degree.
Featured image: Movement of Subducted Tectonic Plates in Earth’s Mantle
Image credit: Erin Walden, Creative Commons Attribution
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