Maya Ellison
The Earth is facing a plastic problem, with trillions of tiny plastic particles polluting environments worldwide. Marine ecologist Melanie Bergmann estimates that only 1% of the plastic entering the oceans annually from municipal solid waste has been detected, meaning that the whereabouts of the remaining 99% is unknown. While plastic pollution is a pressing issue, it is important to note that a part of the Earth is also naturally plasticized. The asthenosphere, a layer of the Earth's upper mantle, behaves like plastic due to high pressure and temperature conditions, allowing for slow flow and deformation of its material. This plasticity is crucial for tectonic plate movement and contributes to geological phenomena such as earthquakes.
| Characteristics | Values |
|---|---|
| Name of the layer | Asthenosphere |
| Location | Part of the Earth's upper mantle |
| Composition | Solid rock |
| Behaviour | Behaves like plastic due to high pressure and temperature |
| Role | Facilitates tectonic activity, allowing the movement of tectonic plates |
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What You'll Learn
The Earth's asthenosphere is plasticized
The Earth's lithosphere, which consists of the Earth's crust and the uppermost portion of the mantle, floats on top of a mechanical layer known as the asthenosphere. This layer is plasticized due to the intense heat and pressure present at that depth. The asthenosphere is a vital part of the upper mantle, which facilitates tectonic activity and contributes to the dynamic nature of our planet.
The asthenosphere is located 80 to 200 kilometres beneath the Earth's surface and has a density of about 3.3 g/cm3. It is composed of solid rock, but due to the high temperature and pressure, it behaves plastically. The temperature in the asthenosphere sits at around 1500°C, and it is this heat that gives the layer its fluid-like properties. The pressure, however, keeps the rock solid and prevents it from melting.
The term 'plastic' refers to the ability of the asthenosphere to flow slowly over time, similar to how silly putty can be deformed and reshaped when pressure is applied. This plasticity is crucial for the movement of tectonic plates, as it allows the lithosphere to ride on top of it. The movement of the asthenosphere is driven by convection currents caused by heat from the Earth's core, which leads to geological phenomena such as earthquakes and volcanic eruptions.
Seismic wave studies have shown that certain types of waves travel through the asthenosphere, indicating that it is solid but can deform over time. This understanding is supported by research in geology and plate tectonics. The asthenosphere is unique to Earth and is not found on any other planet in our solar system. Its presence provides the necessary lubrication for plate tectonics, contributing to the dynamic nature of our planet.
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The asthenosphere is part of the upper mantle
The mechanical layer of the Earth that is both plastic and completely solid is the asthenosphere, which is a part of the Earth's upper mantle. The asthenosphere is composed of solid rock but behaves like plastic due to the high temperature and pressure at that depth. The intense heat and pressure turn rock ductile, allowing it to move at rates of deformation measured in cm/yr over lineal distances of thousands of kilometres. This plasticity is crucial for the movement of tectonic plates, as it allows the lithosphere to ride on top of the asthenosphere.
The asthenosphere is located between 80 and 200 km (50 to 120 miles) below the Earth's surface and extends to a depth of approximately 700 km (430 miles). The upper part of the asthenosphere is believed to be the zone upon which the rigid and brittle lithospheric plates of the Earth's crust move about. The lithosphere is the solid, outer part of the Earth, extending to a depth of about 100 km (62 miles) and includes both the crust and the brittle upper portion of the mantle.
The transition from the lithosphere to the asthenosphere is sharp and marked by a large velocity drop. This transition is known as the lithosphere-asthenosphere boundary (LAB). The LAB is a mechanical boundary defined by seismic data, reflecting the transition from the rigid lithosphere to the ductile asthenosphere. The LAB is also a thermal boundary layer, where heat is transported differently above and below it, and a rheological boundary, where the viscosity drops below a certain level.
The asthenosphere is an important part of the Earth's geological processes, facilitating tectonic activity and contributing to the dynamic nature of the planet. Convection currents generated within the asthenosphere push magma upwards through volcanic vents, creating new crust. This movement of magma also results in earthquakes and volcanic eruptions.
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The outer core of the Earth is plasticized
The Earth is composed of four layers, with the core being the hottest part of the planet. The core is made of two layers: the outer core, which borders the mantle, and the inner core, separated by the Bullen discontinuity. The outer core is about 2,200 kilometres (1,367 miles) thick and is composed of liquid iron, nickel, and other light elements. The nickel-iron alloy of the outer core is very hot, with temperatures ranging from 4,500° to 5,500° Celsius (8,132° to 9,932° Fahrenheit). The liquid metal of the outer core has low viscosity, making it easily deformed and malleable.
The outer core's high temperature and pressure cause it to behave like a plastic material. The churning metal of the outer core creates and sustains the Earth's magnetic field. The dynamo theory attributes the eddy currents in the nickel-iron fluid of the outer core as the principal source of this magnetic field. The outer core's composition and behaviour are influenced by the presence of light elements, which must have been abundant during the Earth's formation and have specific characteristics to be incorporated into the core.
The outer core's density is lower than expected for iron or nickel alloys, suggesting the presence of lighter elements. Recent estimates indicate the presence of hydrogen, carbon, oxygen, silicon, sulfur, and other elements in small percentages by weight. The determination of the exact composition of these light elements is challenging but crucial for understanding the Earth's core formation history.
The outer core's high temperature is due to the decay of radioactive elements, leftover heat from planetary formation, and the release of heat as the liquid outer core solidifies near the inner core. The heat from the outer core drives convection currents, which contribute to the movement of tectonic plates and various geological phenomena, such as earthquakes and volcanic eruptions. As the outer core cools, the liquid at the inner core boundary freezes, causing the solid inner core to grow at the expense of the outer core.
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Plastic pollution in oceans
Our oceans are inundated with plastic pollution, threatening marine life and ecosystems. Plastic pollution in the oceans has become a global crisis, with billions of pounds of plastic found in swirling convergences that make up about 40% of the world's ocean surfaces. This crisis is not limited to a specific region but extends from the equator to the poles, encompassing Arctic ice sheets and the sea floor. It is estimated that there are currently 15-51 trillion pieces of plastic in our oceans, with not a single square mile of surface ocean water left untouched by this pollution.
The primary sources of ocean plastic pollution are rivers and fishing gear. While most plastic in coastal waters originates from land-based sources, the Great Pacific Garbage Patch, located between Hawaii and California, is an exception. Approximately 80% of the plastic in this garbage patch comes from fishing activities at sea, including abandoned fishing nets, buoys, eel traps, crates, and oyster spacers. These larger objects are breaking down into smaller pieces, which are more challenging to clean up, and the longer they remain in the water, the more problematic the issue becomes.
The impact of plastic pollution on marine life is devastating. Sea turtles, for example, can mistake floating plastic garbage for food, leading to choking, internal injuries, or starvation. Research indicates that half of the world's sea turtles have ingested plastic. Additionally, plastic ingestion has been observed in hundreds of thousands of seabirds annually, reducing their stomach storage volume and causing starvation. It is estimated that 60% of all seabird species have consumed plastic, and this number is projected to rise to 99% by 2050. Marine mammals also fall victim to plastic pollution, either by ingesting it or becoming entangled in derelict fishing nets and other plastic debris.
The Center for Biological Diversity is actively addressing this issue by petitioning the U.S. Environmental Protection Agency to regulate plastics as a hazardous pollutant under the Clean Water Act. They are also taking legal action against companies that produce plastic consumer goods, pushing for better control of their runoff, and challenging the construction of new ethane cracker plants. While these efforts are commendable, more urgent action is needed to address the global plastic pollution crisis, reduce plastic production, and improve waste management practices worldwide.
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Plastic pollution in soil
The presence of microplastics in agricultural soils has been a growing area of scientific study, with 60% of microplastic contamination studies from 2018 conducted in Asia, particularly in China. Europe and Africa also account for a significant proportion of these studies, highlighting the global nature of the problem. Plastic mulch films, used to retain soil moisture, and plastic-coated fertilisers are common sources of plastic pollution in soils. The plastic types used for mulching are typically LDPE, LLDPE, and HDPE, with thicknesses ranging from 10 to 80 μm. These plastics do not readily degrade in the soil, leading to a build-up of harmful residues.
Another source of plastic contamination in soils is the use of sewage sludge as fertiliser. Wastewater treatment plants (WWTPs) are not fully effective in removing plastics, and microplastics are often released into the environment through sewage sludge application. The concentration of microplastics in the soil is directly related to the quantity and frequency of sewage sludge use, as demonstrated by studies in China.
The effects of microplastics on soil ecosystems are influenced by their intrinsic characteristics, including polymer type, shape, size, and abundance. While research on the long-term impacts is still ongoing, microplastics have the potential to disrupt soil nutrient cycling and food production. Additionally, plastic pollution in soils can affect the distribution, activity, physiology, and growth of soil flora, fauna, and microorganisms.
The ubiquitous presence of plastics in the environment, coupled with inadequate waste disposal, poses risks to the economy, human health, and the environment. As plastic waste breaks down, it can contaminate soil, leading to potential ecological risks and adverse effects on terrestrial wildlife. The chemicals present in plastics can cause intestinal blockages and toxicity in animals, leading to malnutrition or death.
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Frequently asked questions
The asthenosphere, a part of the Earth's upper mantle, is completely plasticized.
The asthenosphere is composed of solid rock.
The intense heat and pressure at the depth of the asthenosphere cause it to behave like plastic.
The asthenosphere's plasticity allows for the movement of tectonic plates, facilitating tectonic activity and contributing to the dynamic nature of our planet.
