Where Did Earth's Ancient Oceans Go?

To understand the evolution of the Earth, it is essential to study the subduction zones. The tectonic plates of the oceans are being subducted under the continental plates, or under other oceanic plates. Examples include the Pacific Ocean moving under Japan, and subductions within the Mediterranean region. Plate reconstruction models generally agree that about 130 million years ago, there was a peak in the amount of subduction happening. So the maps by Shephard and colleagues could provide independent evidence for this event.

Grace Shephard shows us computer animations reversing these evolutionary processes. She brings back to the surface oceans that have been buried deep inside the mantle for millions of years. It may look like a game, but it illustrates an important point:

Studying these processes in new ways opens up new questions. That is something we welcome, because we need to find out what questions to ask and what to focus on in order to understand the development of the Earth. We always have to keep in mind what is an observations and what is a model. The models need to be tested against observations, to make way for new and improved models. It is an iterative procedure.

Why are the models of the Earth’s interior important?

It is a fundamental way of understanding more about our planet, the configuration of continents and oceans, climate change, mountain building, the location of precious resources, biology, etc. Lines of evidence in the past can be crucial for insight into what will happen in the future, and is critical for the interaction of society and the natural environment.
Earth 1 million years from now

Based on these models, can you predict what the Earth will look like in 1 million years?

If you look at Earth from space, the distribution of continents and oceans will then look much the same, even though life, the climate and sea level may have dramatically changed. If we move even further ahead, say 10 or 100 million years, it is very hard to say how oceans may be opening and closing, but we have some clues. Some people think that the Atlantic will close, and others think the Arctic or Indian oceans will close. We can follow the rules of the past when we look to the future, but this task keeps geoscientists very busy.

Will we be able to predict earthquakes?

It is a holy grail of the community, but we cannot predict earthquakes. Modelling and investigating processes across different scales helps us understand how the Earth system works.

“There are so many questions to be answered. We still need to understand so much more about our present day Earth – and our past Earth. For instance, our current plate tectonics models can take us back pretty confidently to 200 million years ago. I have a colleague who is looking at the past back to 1 billion years. To do that, we need to learn much more about the surface and the deep mantle,” says Grace Shephard.

She chose to move to Norway for many reasons. One of them was the country’s proximity to the Arctic; a region where relatively little is known about subduction, volcanic eruptions and plate tectonics far back in time.

“To me, being a geoscientist is like working in a wonderland. I am able to use lots of different tools and look at different time scales. That is what I really enjoy doing. And I like the interdisciplinary approach. I work with colleagues and collaborators from all over the world. That is a reason why we need to make our models publicly available.”
 

Using information from earthquake data, images of the Earth’s interior via computer models can be generated – this technique is called seismic tomography.

Similar to medical X-ray and CT scans that look for features within the human body, these models image the internal structure of the Earth.

There are different types of data and ways of processing them, which has lead to alternative seismic tomography models.

Thus, a given seismic tomography model is just one snapshot into the present-day structure, which has been shaped by hundreds of millions to billions of years of Earth’s history.