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Ringwoodite and the Deep Water Cycle

Anh Nguyen
Readability
6.7

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The water in the oceans has travelled vast distances. It has even time spent deep below the surface of the Earth, trapped inside the mineral ringwoodite.

Oceans cover 71% of the Earth’s surface. They play an important role in the water cycle that circulates water through the atmosphere. But did you know that there’s also a deep water cycle? It describes how tectonic plates water carry water into the Earth’s mantle. There, it’s absorbed by a mineral called ringwoodite. Later, the water escapes the ringwoodite and travels back to the surface inside magma.

Image of the water cycl
Image of the water cycle (https://www.istockphoto.com/ca/portfolio/normaals?mediatype=illustration">normaals via https://www.istockphoto.com/ca/vector/water-cycle-graphic-scheme-vector-isometric-illustration-gm907850942-250072321">iStockphoto).

What is ringwoodite? How does it form? 

Until recently, scientists had never seen ringwoodite from inside the Earth. To study the mineral, they had to synthesize it in a lab or extract it from meteorites. In 2014, a tiny sample of the mineral was extracted from the Earth for the first time. A grain was found inside a diamond mined in Brazil. The tiny fragment was less than 40 micrometres long.

Did you know?

If you like jewellery, you may be familiar with the gemstone peridot, which is the gem form of olivine!

The diamond originally came from the transition zone of the Earth’s mantle. The transition zone is located several hundred kilometres below the surface. That’s where high temperatures and pressures create ringwoodite out of olivine, another mineral. 

From left to right: samples of peridot, ringwoodite and olivine
From left to right: samples of peridot, ringwoodite and olivine (Sources: Rob Lavinsky [CC BY-SA 3.0] via https://commons.wikimedia.org/wiki/File:Forsterite-Olivine-4jg54a.jpg">Wikimedia Commons, Jasperox [CC BY 3.0] via https://commons.wikimedia.org/wiki/File:BlueRingwoodite.jpg">Wikimedia Commons and Aomai [CC BY 3.0] via https://commons.wikimedia.org/wiki/File:6olivine2645.jpg">Wikimedia Commons).

 

Are you familiar with the theory of plate tectonics? It describes how the Earth’s surface is made up of rocky plates. These plates sit on top of the mantle. Scientists think that the olivine that became the ringwoodite in the Brazilian diamond came from one of these plates. The plate was located at the bottom of the ocean. It pulled the olivine deep below the surface. It also brought some ocean water with it. 

In the transition zone, the olivine was heated and compressed into ringwoodite. Eventually, a diamond formed around the ringwoodite. Then, a volcano brought the diamond up to the surface.

Did you know?

Traces of ringwoodite have been found in stones from the Tenham meteorite shower.

Ringwoodite is formed in the transition zone and then carried to the Earth’s surface inside diamonds
Ringwoodite is formed in the transition zone and then carried to the Earth’s surface inside diamonds (© 2019 Let’s Talk Science).

 

Ringwoodite can absorb water. But it can’t absorb water in liquid, solid or gas form! High temperatures and pressures don’t just transform olivine into ringwoodite. They also cause water molecules to split. This creates hydroxyl radicals (-OH). Pores in the ringwoodite absorb the hydroxyl radicals. This traps the broken-down water inside the mineral’s molecular structure.

There were hydroxyl radicals in the ringwoodite trapped in the Brazillian diamond. The weight of the water was about 1% of the total weight of the sample. Scientists compared this to the total amount of ringwoodite estimated to be in the Earth’s mantle. It looks like the amount of water deep below the surface of the planet is about equal to the amount in the oceans!

What Is Ringwoodite’s Role in the Deep Water Cycle?

The deep water cycle circulates ocean water deep below the planet’s surface and back up again.
Water is carried below the Earth’s surface at subduction zones. Subduction happens when an oceanic plate slides under a continental plate. 

Below the surface, water helps create magma and form volcanoes. When a volcano erupts, the magma reaches the surface in the form of lava.  

Simplified deep water cycle showing how water moves in the mantle and crust
Simplified deep water cycle showing how water moves in the mantle and crust (© 2019 Let’s Talk Science).

 

Researchers have looked at how magma forms in the transition zone. First, they analyzed seismic data related to earthquakes and volcanic activity. Then, they synthesized ringwoodite in their lab. They exposed the mineral to the same high temperatures and pressures found in the transition zone. The ringwoodite began to melt, releasing some of its water. The water decreased the melting point of the rock, and this allowed magma to form.

People can’t really use the water found deep below the Earth’s surface. But it’s important to understand how water travels from the surface to the mantle and back up again. 

The deep water cycle is an important way that the planet cycles its water. It also highlights how tectonic plates move and how volcanoes form. These processes show how water, gases and minerals are constantly moving between the Earth’s surface and its interior.

Did you know?

In 2018, scientists discovered the first freely formed H2O molecules in the Earth’s mantle. The molecules were compressed within diamonds as fragments of water-ice called “ice-VII.” 

Starting Points

Connecting and Relating

  • Have you seen or heard of the mineral peridot before? In what context? 
  • Would you drink water that was produced from ringwoodite? Why/why not?

Connecting and Relating

  • Have you seen or heard of the mineral peridot before? In what context? 
  • Would you drink water that was produced from ringwoodite? Why/why not?

Relating Science and Technology to Society and the Environment

  • Could the fact that large amounts of water are tied up in the Earth’s mantle impact efforts to conserve or protect water sources on the Earth’s surface? Explain.
  • Do you think this type of research will get less funding because it is not immediately economically beneficial? Explain.
  • Do you think that ringwoodite could somehow be used as an alternate source of water in the future? What risks would come with this?

Relating Science and Technology to Society and the Environment

  • Could the fact that large amounts of water are tied up in the Earth’s mantle impact efforts to conserve or protect water sources on the Earth’s surface? Explain.
  • Do you think this type of research will get less funding because it is not immediately economically beneficial? Explain.
  • Do you think that ringwoodite could somehow be used as an alternate source of water in the future? What risks would come with this?

Exploring Concepts

  • How is ringwoodite formed within the Earth?
  • How do plate tectonics and volcanoes influence the rocks and minerals that are available on the Earth’s surface?
  • What role does water play in melting rock?

Exploring Concepts

  • How is ringwoodite formed within the Earth?
  • How do plate tectonics and volcanoes influence the rocks and minerals that are available on the Earth’s surface?
  • What role does water play in melting rock?

Media Literacy

  • While volcanoes are a natural part of the rock cycle, only the destructive side is addressed in popular media accounts. Why do you think this is the case?

Media Literacy

  • While volcanoes are a natural part of the rock cycle, only the destructive side is addressed in popular media accounts. Why do you think this is the case?

Teaching Suggestions

  • This article can be used to support teaching and learning of Earth Science, Minerals and Earth materials and processes related to rocks & minerals, water cycle, Earth’s interior, volcanoes and plate tectonics. Concepts introduced include mineral, peridot, mantle, water cycle, magma and lava. 
  • Before reading this article, teachers could provide students with a Vocabulary Preview to help students access prior knowledge and introduce new terms. Download ready-to-use reproducibles using the Vocabulary Preview learning strategy for this article in [Google doc] and [PDF] formats.
  • After reading this article, teachers could have students consolidate the key points made in the article by conducting a Key Round Robin learning strategy. Download ready-to-use reproducibles using the Key Ideas Round Robin learning strategy for this article in [Google doc] and [PDF] formats. Download a sample student response to the Key Ideas Round Robin learning strategy student for this article in [PDF] format.

Teaching Suggestions

  • This article can be used to support teaching and learning of Earth Science, Minerals and Earth materials and processes related to rocks & minerals, water cycle, Earth’s interior, volcanoes and plate tectonics. Concepts introduced include mineral, peridot, mantle, water cycle, magma and lava. 
  • Before reading this article, teachers could provide students with a Vocabulary Preview to help students access prior knowledge and introduce new terms. Download ready-to-use reproducibles using the Vocabulary Preview learning strategy for this article in [Google doc] and [PDF] formats.
  • After reading this article, teachers could have students consolidate the key points made in the article by conducting a Key Round Robin learning strategy. Download ready-to-use reproducibles using the Key Ideas Round Robin learning strategy for this article in [Google doc] and [PDF] formats. Download a sample student response to the Key Ideas Round Robin learning strategy student for this article in [PDF] format.

Learn more

Deep Earth has Oceans' Worth of Water, $10 Diamond Reveals (2014) 

CBC news report on research into the presence of water in the Earth’s mantle.

Exploring Magma (2012) 

Video (1:43 min.) from Discovery introducing some of the features of magma from the imaginary vantage point of inside of a volcano’s magma chamber.

6 Fascinating Facts About the Earth's Mantle (2019) 

This article from ThoughtCo discusses interesting facts about the Earth’s mantle from the minerals found there to the activities that take place there to how it’s being modeled in a lab.

References

Cordua, B. (2014, May). Ringwoodite - The true story. Mindat.

Earth Observatory of Singapore. (n.d.). What is the difference between magma and lava?

Goes, S. (2018, March 14). Subduction through the mantle transition zone: Sink or stall? European Geosciences Union Blogs

Kawazoe, T. (n.d.). High-pressure synthesis of deep mantle minerals. Hiroshima University.

Lovett, R. A. (2014, March 12). Tiny diamond impurity reveals water riches of deep Earth. Nature.

Water Encyclopedia. (n.d.). Volcanoes and water.