Creation of the Great Lakes | How the Earth Was Made (S1, E7) | Full Episode | History

HISTORY

23 Jan 202145:12

EducationalLearning

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TLDRThe video explores the geological history behind the formation of North America's Great Lakes. It pieces together clues, like ancient seas and coral reefs, glaciers, and thundering Niagara Falls, to unravel the mystery. Massive ice sheets bulldozed the landscape over 10 devastating ice ages, carving out basins later filled by the lakes. Born just 12,000 years ago, the Great Lakes may one day disappear again as geological forces continue shaping the Earth. Their story reveals our dynamic planet's extraordinary past and ever-changing future.

Takeaways

😲 The Great Lakes hold 20% of the world's freshwater and provide drinking water for 10% of Americans
😎 Vast underground salt mines exist below Lakes Huron and Michigan, accidentally discovered while drilling for oil
🌊 Ancient coral reefs and fossilized sea creatures provide evidence that the area was once covered by tropical seas
⛰️ Thousands of drumlin hills act as clues, pointing to the direction that giant glaciers moved across the landscape
❄️Huge ice sheets repeatedly advanced and retreated across North America, carving out the basins that became the Great Lakes
💧 As the glaciers melted, vast amounts of meltwater drained away through spillways, reducing the lakes to their present sizes
🔥Basalt rock discovered on the floor of Lake Superior proves there were once active volcanoes and rift valleys
🕰 Measuring the rate of retreat of Niagara Falls helps date the age of the Great Lakes to just 12,000 years
🚣‍♂️ Ancient beaches around the Great Lakes provide evidence that they were once much bigger 'superlakes'
⏳ Geologists predict the Great Lakes may temporarily disappear in the future before refilling when the next ice age comes

Q & A

What evidence first suggested there was once an ancient sea in the Great Lakes region?
-Vast underground salt deposits found by accident while drilling for oil provided evidence that there was once an ancient briny sea in the region.
What is the Niagara Escarpment and what role does it play?
-The Niagara Escarpment is a vast wall of dolostone rock that forms the boundaries of Lakes Michigan, Huron and Erie. It channels water from the upper Great Lakes over Niagara Falls.
How did scientists determine the age of Niagara Falls?
-By measuring the rate of erosion and the steady movement of the falls upstream over time. This allowed them to calculate that the falls are approximately 12,000 years old.
What evidence points to glaciers having carved out the Great Lakes?
-The presence of thousands of drumlins (teardrop-shaped hills) across the landscape, all pointing north in the direction the ice sheets moved from.
Why is Lake Superior so much deeper than the other Great Lakes?
-Lake Superior lies in an ancient rift valley lined with hard volcanic basalt rock. This made it more vulnerable to being gouged out deeply by glaciers.
What happened when the glaciers retreated 14,000 years ago?
-Vast lakes even larger than the modern Great Lakes were created, like Lake Iroquois. But soon huge volumes of meltwater drained away rapidly through outlets like the St. Lawrence Seaway.
How might future ice ages affect the Great Lakes?
-Future ice sheets could carve the lake basins even deeper before retreating and allowing them to fill with water again.
Why are Great Lakes water levels currently falling?
-It's mainly caused by isostatic rebound - the crust bouncing back upwards after being compressed by immense glaciers during the last ice age.
What does the future hold for Niagara Falls and the Great Lakes system?
-Niagara Falls will eventually cut back through the Niagara Escarpment into Lake Erie, lowering lake levels dramatically. The lakes may even temporarily disappear during future ice ages.
What is the key message or conclusion about the Great Lakes from a geological perspective?
-The Great Lakes system formed relatively recently in geological history and continues to evolve dynamically over time. The lakes are an ever-changing transient feature shaped by the long-term geological processes.

Outlines

00:00

🌊 Formation of the Great Lakes

The Great Lakes of North America hold 20% of the world's freshwater. Geologists investigate the origins of these lakes, believing clues lie in ancient coral reef fossils, vast underground salt mines, the torrential flow of Niagara Falls, and a mile-high glacier.

05:04

🐚 Ancient Coral Reef Discovery

Geologist John Zawiskie discovers fossilized coral reef sponges on Thunder Bay Island in Lake Huron, dating back 385 million years when the region was covered in warm tropical seas. Successive coral reefs decayed into limestone, which was converted into harder dolostone by the evaporating briny sea.

10:06

🌊 Niagara Falls Holds a Clue

Niagara Falls provides a crucial clue to date when freshwater first began flowing into the Great Lakes. Geologist Charles Lyell realized the Falls were gradually moving upstream as water wore away the cliff. By measuring the rate of retreat, Lyell tried to calculate the age of the Falls and lakes.

15:12

❄️ Tracking the Glaciers

Glaciologist Andreas Bauder studies a Swiss glacier's dramatic movement and landscape transformation abilities. The immense weight and resulting conveyor belt motion bulldozes rocks that lodge in the ice, leaving piles behind when the glacier melts and retreats.

20:13

🏔 Giant Erratic Boulders

Geologist John Menzies finds evidence near Niagara Falls of a vast ice sheet including granite erratic boulders transported for hundreds of miles. Parallel scratches on the bedrock and thousands of drumlin hills all point to the same culprit that carved out the Great Lakes.

25:16

🔥 A Volcanic Surprise

Geologist Henry Halls discovers a basalt-lined canyon at the bottom of Lake Superior, evidence of ancient intense volcanic activity when hot magma welled up through a rift valley in the Earth's crust. The thick volcanic rocks made the lake basin vulnerable to deep carving by ice sheets.

30:19

😎 Beachcombing for Ancient Shorelines

John Menzies drives uphill 400 feet above Lake Ontario to stand on the shoreline of glacial Lake Iroquois from 10,000 years ago. Prehistoric beaches now buried under the landscape provide evidence that lakes were once vastly bigger before dramatic flooding drained the excess water.

35:19

🌊 When Will the Lakes Vanish?

As isostatic rebound lifts the Earth's crust, rivers feeding the Great Lakes are cut off, gradually lowering water levels. And Niagara Falls is forecast to erode back to Lake Erie in a few thousand years, emptying Lakes Michigan, Huron, Superior and draining almost all of Lake Erie.

40:22

🔮 The Lakes' Uncertain Future

The Great Lakes have only existed for 12,000 years, a blink in geological history. While lake levels are currently falling, scientists predict new ice ages will come, carving the basins deeper before they refill. The lakes are ever-changing, like the evolving Earth itself.

Mindmap

Keywords

💡Great Lakes

The Great Lakes of North America are a connected series of large freshwater lakes spanning the Canada-US border. They are referred to extensively throughout the video as the central focus of the geological history being uncovered.

💡ice sheets

Massive glaciers of ice that covered large portions of North America during past ice ages. Their movement and melting are shown to be key forces behind the formation of the Great Lakes basins.

💡drumlins

Elongated teardrop-shaped hills made of glacial debris. Their orientation and distribution provide evidence for the direction and intensity of past ice flows.

💡dolostone

A very hard metamorphic carbonate rock that acted as a protective basin holding the Great Lakes. Formed when an ancient sea evaporated and altered underlying limestone.

💡Niagara Falls

Important geological feature marking the outlet of the upper Great Lakes over the Niagara Escarpment. Dating the falls provides a maximum age for the existence of the lakes.

💡crustal rebound

The slow uplift of land in regions once weighed down by heavy ice sheets. As the crust bounces back, lake levels fall, drainage patterns shift, and shorelines move over time.

💡erratic boulders

Massive boulders transported long distances by glaciers. Their displacement from source regions provides evidence of past ice flows.

💡striations

Scratches or gouges carved into bedrock by rocks embedded in glacier ice. They reveal the direction of ice movement.

💡interglacials

Warm periods between ice ages marked by layers of organic sediments and soil formation. Provide snapshots of ice retreat and landscape exposure.

💡Lake Iroquois

A prehistoric proglacial lake that preceded the Great Lakes, with shorelines hundreds of feet above modern lake levels. Evidence for drainage of vast post-glacial meltwater.

Highlights

The Great Lakes hold 20% of the world's freshwater and provide drinking water for nearly 10% of Americans.

Vast salt deposits provide evidence of an ancient ocean that existed where the Great Lakes are now.

Fossilized sea sponges show that an ancient coral reef existed in the Great Lakes region 385 million years ago.

Niagara Falls provide a way to date the age of the Great Lakes to just 12,000 years old.

Thousands of drumlin hills point to an immense glacier that carved out the Great Lakes.

Dark rock layers reveal multiple ice sheet attacks that helped form the deep Great Lake basins.

Ancient rivers left valleys that made the landscape vulnerable to fast-moving destructive super ice.

A basalt-lined canyon shows that Lake Superior lies in an ancient volcanic rift valley.

Ancient beaches provide evidence of vast prehistoric lakes that predated the Great Lakes.

Giant potholes and canyons prove catastrophic floodwaters drained the prehistoric lakes.

The Great Lakes only reached their present state 12,000 years ago.

Post-glacial crustal rebound is causing Great Lakes water levels to fall.

In the future, Niagara Falls erosion could cause catastrophic Great Lakes drainage.

The Great Lakes have only existed for a blink of an eye geologically, but will continue evolving.

New ice ages are expected to reshape the Great Lakes again in the future.

Transcripts

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