How the Andes mountains killed a group of whales some sloths and a load of seals. 4 times.

In the driest desert in the world, the Atacama desert in Chile, there are a host of sea life skeletons preserved in the ground.

The Atacama Desert is not the sort of place life likes — it is regularly used as a filming location to represent Mars — but in the Miocene this place was ocean side property.

The Miocene is 23.03 million years ago to 5.333 million years ago — back when the first Apes were evolving and horse-like sloth-like mammals (the Chalicotheres) roamed Europe and North America, the Atacama desert was more of a beach with the Andes mountains touching the sea and growing. The planet more generally was much hotter than it is now and the Arctic had melted almost completely.

So there were loads of marine life there?

Yeah basically. The ocean was rich, and so it probably isn’t surprising to find fossilised skeletons, right? Yes and No. Yes it is normal to find skeletons of marine life on land, but what is strange is how many skeletons we find in one location of all different types of animals without there being a mass extinction! And then what’s even crazier, is that this happened at four different times in 16,000 years.

The theory is that there must have been a Mass Stranding — but, a mass stranding is the outcome of what happened. The animals weren’t necessarily alive when they were beached for it to be classified as a mass stranding.

Mass strandings are something we see today, so it probably could have happened before. In this instance, mass stranding seemed to be the case, because of most skeletons were found belly up, inferring that the animals died at sea and then floated to shore, and also, because the skeletons do not have any notable damage and are relatively intact, scavenging animals wouldn’t have had chance to eat so much prey all at once.

Okay so what causes mass strandings?

Causes of beaching

  1. Environment — individuals’ weakness, rough weather, shallowly sloping beach fronts, consuming poisonous food or water, rain and sand disrupting echo location, and changes magnetic poles of Earth are all examples.
  2. ‘Follow Me’ — when large whales follow smaller whales or dolphins and become beached. This stems from the fact that most whales that are beached are social animals, the solitary ones are much less common.
  3. Accidentally Intentional — very very very rarely some Orca’s do beach themselves when they intentionally land themselves on beaches when chasing seals. But it is rare as Orcas are so clever … and terrifying.
  4. Sonar — Human’s typically causing confusion, scaring whales or causing internal haemorrhaging from use of sonar

So what could it be?

Theory 1: Follow Me

The animals must have just beached themselves like normal — basically the ‘Follow Me’ reason. But this theory breaks down, as it wasn’t just one type of whale that was found. Dolphins, seals and aquatic sloths were found in the same sediment. Furthermore, if the seals were alive when they hit shore they could have easily turned around and gone back in the water.

Theory 2: Virus/Bacteria/Illness

Maybe, but again, there are many animal species. It would be highly unusual for one pandemic to hit multiple species at the same time. And then for that to happen in the same location, to the same animals 3 more times over 16,000 years.

Theory 3: Natural Disaster

More likely, but there is usually geological evidence for these types of events as surface earth tends to be heavily disrupted, yet in the Atacama the ground seems to have been laid steadily within this timeframe.

Theory 4: Poison

As human sonar cannot be blamed, we are looking for repeating multiple species mass extinction, the best guess seems to be some kind of poison polluted the waters off the coast of the Atacama and hence killed all the wildlife in that area.

What is your poison?

The best guess is from Algal Blooms. We see them occurring regularly and naturally.

This tends to kill lots of animals as the Algae can cause low oxygen conditions and can create poisonous waste.

But where did it come from and how did it happen 4 times?

This is where the Andes and, more generally, South America’s geography comes in. South America diverts a strong wind current and hence creates a cycle as below. The wind travels strongly north and, as such, has an effect on the sea.

As the wind pushes the water north, the water from below the surface can come up as part of convection. When this happens, nutrient rich water rises up, and provides a wealth of materials at a higher level than before, including algae.

But this happens continuously. When the algae gets to the top of the sea it doesn’t have the food it usually relies on when down on the sea floor and so the algae doesn’t usually cause a problem. It loves to consume iron, and that doesn’t usually exist on the top of the sea.

So what food did the algae eat to bloom so quickly, 4 times only?

The time periods during which these mass strandings happened are close to an earth cycle know as precession. This is essentially how wobbly our earth is and how that changes temperatures on Earth.

Essentially, every 13,000 years the north is closer to the sun and after another 13,000 years the south is. (This is a MASSIVE over simplification and it is contentious and further research could take you to climate denying sites and more). You have been warned...

But, if you can accept that the Earth not only has yearly seasons but also decade and century-esque seasons, it seems the Andes had a particularly cold period where a lot of ice formed, and then suddenly a hot period.

This caused a big melt and hence a lot of water moving from the mountain to the sea. In another part of the Andes, its rock is iron rich. So the ice melt brought sediment to the sea that had lots of iron. And algae loves iron.

Also, another quirk of the geography of South America is something known as El Niño — a weather phenomena that causes warm air to travel from the far east Pacific to the Americas. This phenomena means you can have super drastic climate changes in a very short space of time.

If these two periods overlapped, the warming effect could have doubled up and would’ve had a very drastic effect on the climate.

So this is the theory on how the Sun, Earth and Andes killed a load of whales, seals, dolphins and some sloths.


The Earth wobbles, so its average temperature oscillates over thousands of years. Snow and ice built up on the Andes during a cold period. This cold period was quickly followed by a hot period, the speed of which was probably caused by El Niño, which melted the ice and brought iron rich sediment to the sea.

The Andes also diverts wind up north and hence creates conditions where cold sea water from the depths, is raised to the surface near the coast.

When these both happened, algae likely bloomed and caused toxicity levels in the sea which killed marine life, which then washed ashore and became buried in sediment over time.

This post is entirely dedicated to this video by Eons. It is an incredible channel which is a joy in story telling. Thank you!

From PBS’s Eon’s Youtube Channel.

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