Earth history

A giant lava lamp inside the earth might be flipping the planet’s magnetic field

Signals from violent earthquakes help reveal the landscape of the planet's insides.

If you could travel back in time 41,000 years to the last ice age, your compass would point south instead of north. That’s because for a period of a few hundred years, the earth’s magnetic field was reversed. These reversals have happpened repeatedly over the planet’s history, sometimes lasting hundreds of thousands of years. We know this from the way it affects the formation of magnetic minerals, that we can now study on the earth’s surface.

Several ideas exist to explain why magnetic field reversals happen. One of these just became more plausible. My colleagues and I discovered that regions on top of the earth’s core could behave like giant lava lamps, with blobs of rock periodically rising and falling deep inside our planet. This could affect its magnetic field and cause it to flip. The way we made this discovery was by studying signals from some of the world’s most destructive earthquakes.

Around 3,000 km below our feet – 270 times further down that the deepest part of the ocean – is the start of the earth’s core, a liquid sphere of mostly molten iron and nickel. At this boundary between the core and the rocky mantle above, the temperature is almost 4,000 degrees Celsius, similar to that on the surface of a star, with a pressure more than 1.3 million times that at the earth’s surface.

On the mantle side of this boundary, solid rock gradually flows over millions of years, driving the plate tectonics that cause continents to move and change shape. On the core side, fluid, magnetic iron swirls vigorously, creating and sustaining the Earth’s magnetic field that protects the planet from the radiation of space that would otherwise strip away our atmosphere.

Because it is so far underground, the main way we can study the core-mantle boundary is by looking at the seismic signals generated by earthquakes. Using information about the shape and speed of seismic waves, we can work out what the part of the planet they have travelled through to reach us is like. After a particularly large earthquake, the whole planet vibrates like a ringing bell, and measuring these oscillations in different places can tell us how the structure varies within the planet.

In this way, we know there are two large regions at the top of the core where seismic waves travel more slowly than in surrounding areas. Each region is so large that it would be 100 times taller than Mount Everest if it were on the surface of the planet. These regions, termed large-low-velocity-provinces or more often just “blobs”, have a significant impact on the dynamics of the mantle. They also influence how the core cools, which alters the flow in the outer core.

Several particularly destructive earthquakes over recent decades have enabled us to measure a special kind of seismic oscillations that travel along the core-mantle boundary, known as Stoneley modes. Our most recent research on these modes shows that the two blobs on top of the core have a lower density compared to the surrounding material. This suggests that material is actively rising up towards the surface, consistent with other geophysical observations.

New explanation

These regions might be less dense simply because they are hotter. But an exciting alternative possibility is that the chemical composition of these parts of the mantle cause them to behave like the blobs in a lava lamp. This would mean they heat up and periodically rise towards the surface, before cooling and splashing back down on the core.

Such behaviour would change the way in which heat is extracted from the core’s surface over millions of years. And this could explain why the earth’s magnetic field sometimes reverses. The fact that the field has changed so many times in the earth’s history suggests that the internal structure we know today may also have changed.

We know the core is covered with a landscape of mountains and valleys like the earth’s surface. By using more data from earth oscillations to study this topography, we will be able to produce more detailed maps of the core that will give us a much better understanding of what is going on deep below our feet.

Paula Koelemeijer, Postdoctoral Fellow in Global Seismology, University of Oxford.

This article first appeared on The Conversation.

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“My body instantly craves chai and samosa”

German expats talk about adapting to India, and the surprising similarities between the two cultures.

The cultural similarities between Germany and India are well known, especially with regards to the language. Linguists believe that Sanskrit and German share the same Indo-Germanic heritage of languages. A quick comparison indeed holds up theory - ratha in Sanskrit (chariot) is rad in German, aksha (axle) in Sanskrit is achse in German and so on. Germans have long held a fascination for Indology and Sanskrit. While Max Müller is still admired for his translation of ancient Indian scriptures, other German intellectuals such as Goethe, Herder and Schlegel were deeply influenced by Kalidasa. His poetry is said to have informed Goethe’s plays, and inspired Schlegel to eventually introduce formal Indology in Germany. Beyond the arts and academia, Indian influences even found their way into German fast food! Indians would recognise the famous German curry powder as a modification of the Indian masala mix. It’s most popular application is the currywurst - fried sausage covered in curried ketchup.

It is no wonder then that German travellers in India find a quite a lot in common between the two cultures, even today. Some, especially those who’ve settled here, even confess to Indian culture growing on them with time. Isabelle, like most travellers, first came to India to explore the country’s rich heritage. She returned the following year as an exchange student, and a couple of years later found herself working for an Indian consultancy firm. When asked what prompted her to stay on, Isabelle said, “I love the market dynamics here, working here is so much fun. Anywhere else would seem boring compared to India.” Having cofounded a company, she eventually realised her entrepreneurial dream here and now resides in Goa with her husband.

Isabelle says there are several aspects of life in India that remind her of home. “How we interact with our everyday life is similar in both Germany and India. Separate house slippers to wear at home, the celebration of food and festivals, the importance of friendship…” She feels Germany and India share the same spirit especially in terms of festivities. “We love food and we love celebrating food. There is an entire countdown to Christmas. Every day there is some dinner or get-together,” much like how Indians excitedly countdown to Navratri or Diwali. Franziska, who was born in India to German parents, adds that both the countries exhibit the same kind of passion for their favourite sport. “In India, they support cricket like anything while in Germany it would be football.”

Having lived in India for almost a decade, Isabelle has also noticed some broad similarities in the way children are brought up in the two countries. “We have a saying in South Germany ‘Schaffe Schaffe Hausle baue’ that loosely translates to ‘work, work, work and build a house’. I found that parents here have a similar outlook…to teach their children to work hard. They feel that they’ve fulfilled their duty only once the children have moved out or gotten married. Also, my mother never let me leave the house without a big breakfast. It’s the same here.” The importance given to the care of the family is one similarity that came up again and again in conversations with all German expats.

While most people wouldn’t draw parallels between German and Indian discipline (or lack thereof), Germans married to Indians have found a way to bridge the gap. Take for example, Ilka, who thinks that the famed differences of discipline between the two cultures actually works to her marital advantage. She sees the difference as Germans being highly planning-oriented; while Indians are more flexible in their approach. Ilka and her husband balance each other out in several ways. She says, like most Germans, she too tends to get stressed when her plans don’t work out, but her husband calms her down.

Consequently, Ilka feels India is “so full of life. The social life here is more happening; people smile at you, bond over food and are much more relaxed.” Isabelle, too, can attest to Indians’ friendliness. When asked about an Indian characteristic that makes her feel most at home, she quickly answers “humour.” “Whether it’s a taxi driver or someone I’m meeting professionally, I’ve learnt that it’s easy to lighten the mood here by just cracking a few jokes. Indians love to laugh,” she adds.

Indeed, these Germans-who-never-left as just diehard Indophiles are more Indian than you’d guess at first, having even developed some classic Indian skills with time. Ilka assures us that her husband can’t bargain as well as she does, and that she can even drape a saree on her own.

Isabelle, meanwhile, feels some amount of Indianness has seeped into her because “whenever its raining, my body instantly craves chai and samosa”.

Like the long-settled German expats in India, the German airline, Lufthansa, too has incorporated some quintessential aspects of Indian culture in its service. Recognising the centuries-old cultural affinity between the two countries, Lufthansa now provides a rich experience of Indian hospitality to all flyers on board its flights to and from India. You can expect a greeting of Namaste by an all-Indian crew, Indian food, and popular Indian in-flight entertainment options. And as the video shows, India’s culture and hospitality have been internalized by Lufthansa to the extent that they are More Indian Than You Think. To experience Lufthansa’s hospitality on your next trip abroad, click here.

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This article was produced by the Scroll marketing team on behalf of Lufthansa as part of their More Indian Than You Think initiative and not by the Scroll editorial team.