USask geoscientist: Three things you might not know about the Earth

The Earth is billions of years old, but USask geoscientists like Dr. Jim Lee (PhD) continue to discover new information about the planet. As the world prepares to recognize Earth Day on April 22, Lee highlights three key points about the planet and the importance of taking care of our home.

Here are three (what I think are) really cool facts about the Earth:

Contrary to popular belief, the Earth is not round. Although it certainly looks round in all of the photos from space, it is not a perfect sphere. Why?

There are many reasons for this, but the main one is that the Earth is rotating. This rotation creates forces acting on the Earth which counteract gravity. These forces which oppose gravity are basically zero at the poles, but get progressively larger towards the equator, resulting in an equatorial bulge in the Earth.

This equatorial bulge means that the distance from the centre of the Earth to the North (or South) Pole is about 21.4 km shorter than the distance to the equator. This shape (called an oblate spheroid) would be analogous to a (very) slightly squashed ball, and is observed with many other rotating planets, such as Jupiter and Saturn.

This non-spherical shape also means that the force of gravity is not the same everywhere on Earth. At the poles (north or south), gravitational attraction is slightly stronger (9.83 m/s2) than at the equator (9.78 m/s2), so if you would ever like to lose some weight quickly, just go somewhere warm and tropical!

In our society today, everyone understands the importance of recycling. Well, the Earth does it too – on a massive scale. In fact, the Earth has two major recycling schemes.

Every day, the Earth’s crust is being created and destroyed. If we think of the Earth’s crust as the thinnest, outermost shell at the surface of the Earth, this shell is actually made up of many large and small pieces, which we call “plates” (think of peeling an orange and putting all of the pieces of peel back onto the orange).

These plates push and pull against each other all over the Earth. Generally, the deeper you go inside the Earth, the hotter it gets, so when plates pull apart, this allows molten rock from the hotter, deeper Earth to flow up to the surface and solidify, creating new crust. When plates collide, one of the plates ends up going (is “subducted”) underneath the other deeper in the Earth, so the subducted plate may melt, thus destroying the crust.

This continuous process of creating and destroying the Earth’s crust is fundamental to the concept of plate tectonics and explains so many things that we observe in the world around us, such as mountains, earthquakes and volcanoes.

We don’t exactly know how long crustal recycling on Earth has been happening (the Earth is very old—in fact, 4.55 billion years old), but it has likely been for a very long time, probably much longer than the first appearance of life on our planet.

A second Earth-scale recycling scheme explains why we have three main types of rocks: igneous (for example, granite), sedimentary rocks (sandstone), and metamorphic (gneiss).

Igneous rocks form when rocks (of any type) melt, forming molten rock (also known as magma) which then cools and hardens. However, rocks (of any type) that are exposed on the Earth’s surface are subject to erosion by wind, water, and rain, which results in the creation of sedimentary rocks. Finally, the movement of the tectonic plates can result in the deformation and reheating of rocks, transforming rocks (of any type) into metamorphic rocks.

This demonstrates how one type of rock can be continually recycled into rocks of any other type, in a never-ending process that geologists call the Rock Cycle.

We know that the Earth has a North magnetic pole and a South magnetic pole, which are associated with the Earth’s magnetic field. Superficially, we can think of the Earth’s magnetic field as being similar to that created by a giant bar magnet—which as everyone knows, has a north end and a south end—placed at the centre of the Earth.

However, unlike a bar magnet, the Earth’s magnetic field is actually created by some very complex fluid motions in the Earth’s outer core: a hot (~3000-7000 ˚C!) liquid shell of molten iron and nickel about 2,889 km deep in the Earth.

Strangely, every once in a while, the magnetic south and north pole switch places. We have direct evidence of this in the geologic rock record going back continuously in Earth history to about 160 million years ago.

We have no idea why this switch happens, but it must be related to the very complicated and chaotic fluid motions in the Earth’s outer core. These “geomagnetic reversals” appear to occur at random throughout history. Over the last 80 million years, they have occurred on average every 450,000 years, but there is no consistent pattern to predict their occurrence. The time between reversals can range from tens of thousands of years to tens of millions of years.

When a geomagnetic reversal happens, we think the Earth’s magnetic field grows weaker and weaker, perhaps down to ~10 per cent of its normal strength, and then begins to grow stronger again, but now with the poles reversed. Moreover, we think this all takes place in a very short (geologically speaking) period of time—anywhere from 2,000 to 12,000 years.

This is a big mystery which geoscientists are still trying to understand. There are also many fascinating questions that remain to be explored. How would biological life be affected in a much weaker magnetic field between geomagnetic reversals? Many organisms such as insects, fish, and birds, also use the Earth’s magnetic field to navigate around the planet (for example, during migration); how would they be affected by a geomagnetic reversal?

If readers are curious about learning more weird and wonderful facts about the Earth, consider enrolling in GEOL 108 (The Earth and How It Works) or GEOL 109 (The Earth and Life Through Time).

Absolutely. In order to take care of anything, we need to know how it works. This could refer to your car, your own body, and indeed, our own planet. To keep automobiles in good health, mechanics need to study how cars work. To keep us in good health, doctors need to study how the human body works. And to keep our planet in good health, we need to study how the Earth works.

This is what geoscientists do. Indigenous peoples all over the world have long understood this by considering themselves as stewards of the land and only one of many connected parts of the whole “Earth system.”

The concept of sustainability is fundamentally based on knowing how the Earth works and what we can do about it. Of the UN’s 17 Sustainable Development Goals (SDGs), the Earth sciences are prominent in over 50 per cent of them, such as good health and well-being, clean water, affordable and clean energy, and climate action.

If we extend the idea that the Earth is like a big recycling plant with fixed (limited) resources, then making a change in one part of the plant may ultimately affect the entire system. This is why the Earth sciences are at the heart of some of the biggest societal challenges that we face today.

In order to solve problems like climate change, food and water security, and poverty, we need geoscientists working with a suite of other experts in science and engineering, social science, and the arts and humanities. Ultimately, by looking after the Earth, we are looking after ourselves, and it is geology which unites all of us under a common theme.