Mad about Science: Formation of the alps

By Brenden Bobby
Reader Staff

The European Alps are among the world’s most recognizable mountain ranges. This range stretches across eight countries and possesses evidence of at least 8,000 years of human habitation. Certainly, such a magnificent collection of mountains must be incredibly ancient, right?

These mountains are actually relatively young, geologically speaking. The bulk of their formation occurred about 40 million years ago — more than 20 million years after most dinosaurs had gone extinct. This seems like an incalculable amount of time, and to a short-lived human it is. In the scope of geological time, however, these mountains are bratty tweens compared to their peers.

The Swiss Alps in the Grindelwald Valle. Courtesy photo.

The Black Hills in South Dakota and Wyoming are the United States’ oldest mountains, believed to be an estimated 1.8 billion years old. These mountains were jutting from the Earth during the Precambrian era, in a time when terrestrial life of any kind did not yet exist. Proto-plants and soft-bodied creatures called the shallow Precambrian seas home. Even the first trilobites wouldn’t scurry about the ocean floor for another 1.3 billion years after the formation of the Black Hills.

The earliest moment of the Alps’ history began 300 million years ago with the supercontinent of Pangaea. Pangaea was beginning to break apart into Gondwana and Laurasia. Over the next 260 million years or so, the continents drifted into the locations we recognize today due to a number of factors, primarily tectonic shifts.

If you were to carve a cross section from the Earth, you’d see a number of layers. Imagine cutting into an avocado. The inner core is a solid mass of iron and nickel — imagine the avocado’s pit. It’s surrounded by a liquid outer core of molten metal and rock. You won’t find this in an avocado, so the best you can do is imagine emulsified red-hot guac swirling around the pit. The mantle surrounds the outer core, which is a mix of molten liquid and solid rock, metal and other elements. This is essentially the flesh of our avocado. Finally, Earth’s crust is a wrap of cooled rock with a variable thickness of three to 43 miles thick. You guessed it: The crust is the avocado’s rind. 

It’s hard to imagine lots of rock moving and shifting around. Rock is heavy, and most of our interactions with large rocks involve watching them roll down hills, not rising up or shifting around on their own. Huge layers of rock actually do shift around beneath our feet, they’re just so massive that we can’t really see them. The movement of these plates occurs due to a chain of events that begin in the inner core of Earth.

Elements within the core emit heat when they radioactively decay. This happens everywhere, but because of the amount of pressure involved from a planet’s worth of matter pressing down on the core, there is a vast quantity of atoms decaying over time. This incredible heat can’t dissipate like it does on Earth’s surface or in space; instead it transfers to nearby structures — in this case, the outer core and the mantle.

The farther from the core you get, the cooler it becomes. 

Most matter behaves similarly when subjected to heat and pressure, even though the tolerances may vary from structure to structure. If you cram a whole bunch of iron into an enclosed space and heat it up, it will act similarly to air under similar conditions. In this way, you can imagine Earth’s mantle acting like a convection oven.

A convection oven works by moving air around the interior of the oven to more evenly cook your food. It disallows hot spots to settle in the air by moving the air around the oven. Convection is a term that describes the process of hot air rising and cool air falling in a cyclical pattern. Rock in the Earth’s mantle does this same thing as heat from the core rises and makes rock in the mantle move around. This moving rock is what causes the tectonic plates to shift.

In the case of the Alps, the African plate was pushed by 10s of millions of years of this convection. It collided with the European plate and slipped over the top of it. This collision didn’t cause the plates to stop moving, but instead it kept pushing the mountain range higher. 

The limestone that makes up most of the mountain range was sediment at the bottom of the Tethys Sea separating Gondwana and Laurasia. This sediment was debris from a vast number of things, ranging from plant life to skeletal remains and sand eroded from larger stones and deposited at the bottom of the ocean. It was compacted by the pressure of the ocean over time, forming into solid stone rather than loose sediment. Fossilized remains of aquatic creatures from the Triassic Period can still be found in the Alps to this day.

In more recent times, the Alps proved to be a refuge for plants and animals — including humans — during the most recent ice age. There are species of plants endemic only to the Alps, having rooted there during the glaciation period between 7,000 and 12,000 years ago. 

As global temperatures rise, the glaciers of the Alps have begun receding. This has a cascading effect on the ecosystem of the entire range. As less water is retained, the volume of waterways changes, erosion occurs and there is less ice reflecting sunlight and heat. This likely isn’t the first such occurrence in the short life of the mountain range, but it probably hasn’t happened at the breakneck speed at which we’re watching it unfold now.

Stay curious, 7B.