Name: 那个时候地中海消失了（That Time the Mediterranean Sea Disappeared）
Uploaded: 2021-05-01T03:34:07.000Z
Duration: 11 min 56 s
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In 2011, paleontologists working on the Spanish island of Minorca announced the discovery

程度副詞

They were the bones of a rabbit, but it wasn't like any rabbit you've ever seen.

For one thing, this bunny was a giant, up to six times heavier than your average cottontail.

It also had short hindlimbs, compared to its forelimbs, and feet that were tipped with

And this rabbit almost certainly couldn't hop.

It had a stiff spine and splayed toes - very different from the flexible spines and tightly

The scientists named this huge bunny Nuralagus rex -- “the Rabbit King of Minorca” -- and

they determined that it ruled its island kingdom during the Pliocene Epoch, from about 5 million

Now, we've talked before about insular gigantism, where small animals that become isolated on

islands evolve into larger forms due to a lack of predators.

And that seems to be what allowed Nuralagus rex to get so big.

But how did the normal-sized ancestor of Nuralagus make it onto a Mediterranean island in the

Well, it looks like the answer to this biological mystery is actually wrapped up in an even

Since the 1800s, scientists have known that the layers under the floor of the Mediterranean

Sea weren't just made up of the usual sediments, like mud and sand.

Instead, they're full of salt crystals -- lots and lots of salt -- forming mega-deposits

so large that they're sometimes called the Mediterranean Salt Giant.

And salt deposits like these are typically found in places where bodies of water have

So the existence of this Salt Giant suggests that, at one point in history, the Mediterranean

But how could a body of water as big as the Mediterranean just...disappear?

It would take decades and more than 1,000 research studies to even start to figure out

the cause -- or causes -- of one of the greatest vanishing acts in Earth's history.

Today, ocean water flows into the Mediterranean Sea from the Atlantic through a narrow passage

between Europe and Africa, called the Strait of Gibraltar.

And that's the main source of water for the Sea.

Some freshwater in the form of rainfall and rivers also flows into it, but that's not

enough to keep the Sea filled up without the water from the Atlantic, because it has very

So, to the geologists who were trying to explain the existence of the Salt Giant, it looked

like the main water source to the Mediterranean had somehow been turned off, like turning

They called this event the Messinian Salinity Crisis, or MSC.

But it wasn't easy to figure out how that

And researchers have been arguing about it since the 1970s.

In the end, they came up with three main hypotheses to answer these questions and explain how

First, some scientists thought there was a global cooling event at the beginning of the

crisis, in the Late Miocene Epoch around 6 million years ago.

If the whole world cooled off into an ice age, then lots of water would've been taken

out of the ocean and frozen in glaciers, reducing the water flow into the Mediterranean Sea

An event of this magnitude would have to have been global, not local.

However, this idea was proved wrong pretty quickly.

Soon after the Salt Giant was discovered, researchers started studying oxygen isotopes

and other geochemical data from sediment and ice cores around the world.

Their data showed that the rest of the Earth wasn't abnormally hot, cold, or dry during

Plus, they found that some of the salt was deposited before any changes in sea level.

So there didn't seem to be a cooling event that was big enough to turn off the flow of

The second idea was that tectonic events had somehow blocked the Mediterranean off from

the Atlantic, and cut off the water flow.

Some researchers thought that shifting ocean crusts slowly blocked off the waterway between

As the water left behind in the deep basin evaporated, it became saltier and saltier,

Other scientists thought that it might have been a combination of shifting crusts and

climate change that made the Mediterranean dry up.

According to this model, the crust under the Strait of Gibraltar rose up over time, reducing

Then, because of changes in regional climate -- like periods of less rain and higher temperatures

-- the amount of freshwater that made it into the Mediterranean varied.

So by this thinking, the MSC didn't happen all at once.

Instead, water levels started to drop after the strait closed, and then fluctuated according

And this hypothesis ended up being … pretty much right!

As geologists began collecting evidence to test these hypotheses, they eventually found

that the MSC was indeed caused by changes in Earth's crust, but those shifts actually

happened repeatedly, not just in one fell swoop.

For example, in sediments near the Nile, geologists found evidence of repeated erosion events,

This meant that the water level dropped, created a new shoreline for a bit, and then dropped

Some researchers estimate that there were 16 climate cycles just in the beginning of

And these changes also correlated pretty closely with what we know about climate cycles.

During periods of decreasing sea level, the position and angle of the Earth changed with

respect to the Sun, so there were periods of lower solar energy, and others of higher

solar energy, which increased evaporation rates in the Mediterranean.

At the same time, an actively folding and uplifting tectonic belt caused water input

Researchers were able to use chemical, and even magnetic, signatures in the sediments

laid down during this time to estimate how long the MSC lasted.

And the data suggest that it went on for over 600,000 years, with the very driest period

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那个时候地中海消失了（That Time the Mediterranean Sea Disappeared）

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