Is the Mystery of Earth's 1.2 Billion Missing Years Solved? | SciShow News

Summary

This video delves into the mystery of the Great Unconformity, a phenomenon where over a billion years of Earth's geological history are missing from the record. Recent research suggests that massive glaciers during the 'Snowball Earth' period eroded and removed vast amounts of rock, which were then recycled into the Earth's mantle. The study also explores the potential connection between this erosion and the Cambrian Explosion, where biodiversity dramatically increased. While further research is needed, these findings offer new insights into Earth's ancient history.

Takeaways

• 🧊 The Great Unconformity is a significant geological mystery where over a billion years of Earth's history is missing from the geologic record.
• 🧗‍♂️ Researchers have proposed that massive glaciers during a period called 'Snowball Earth' may have eroded over a dozen vertical kilometers of rock, contributing to this missing time.
• 📜 The Great Unconformity is characterized by a sudden jump in the age of rock layers, first identified in the Grand Canyon by geologist John Powell.
• 🌍 Geologists have found that around 10 billion cubic kilometers of Earth's crust disappeared, representing nearly a quarter of Earth's history.
• 🔬 By studying zircon crystals, scientists discovered that a significant amount of Earth's land was eroded and recycled into magma during the Snowball Earth period.
• 💎 The presence of these zircon crystals supports the idea that glaciers scoured the Earth around 650 million years ago, depositing the eroded material into the oceans.
• 🧬 The lack of impact craters from before the Cambrian period supports the theory of extensive glacial erosion during Snowball Earth.
• 🔥 One challenge remains in explaining why no new rock layers formed immediately after the glaciers retreated, as Earth's warming occurred before the unconformity ends.
• 🌱 Some researchers suggest that the erosion might have triggered the Snowball Earth conditions, leading to a global glaciation event.
• 🌊 There is a poetic hypothesis that the massive environmental changes during this period could have contributed to the Cambrian Explosion, leading to a dramatic increase in biodiversity.

Q & A

What is 'The Great Unconformity' in geology?

The Great Unconformity refers to places in the geologic record where there is a sudden jump in the aging of rock layers, with a significant amount of time unaccounted for. This phenomenon is marked by missing layers that represent billions of years of Earth's history.

Who first discovered The Great Unconformity, and where?

The Great Unconformity was first discovered by geologist John Powell in 1869 while he was exploring the Grand Canyon. He found that over a billion years of geologic record was missing.

What are the two main hypotheses proposed to explain The Great Unconformity?

The two main hypotheses are: (1) No new sediment was deposited over the missing millennia, or (2) there was massive erosion that removed the geologic record, scraping away the layers of sediment.

How did the researchers study the rocks above and below The Great Unconformity?

Researchers examined the Tapeats Sandstone above the unconformity, which dates to the Cambrian period (about 525 million years ago), and the Vishnu Schist below it, which is over 1.6 billion years old. They looked for clues in the compression of rock layers and the volume of material in the rocks to understand what happened.

What role did zircon crystals play in the researchers' findings?

Zircon crystals were crucial because they survive major geologic processes and capture geochemical conditions when they form. By analyzing isotopes of uranium, oxygen, and hafnium in these crystals, researchers could trace the origin of the material and determine that a significant portion of Earth's land was eroded and subducted into the mantle.

What is 'Snowball Earth,' and how is it related to The Great Unconformity?

'Snowball Earth' refers to a hypothesis that around 650 million years ago, the Earth was completely or mostly covered in ice. The study suggests that massive glaciers during this period were responsible for eroding and removing the missing rock layers, leading to The Great Unconformity.

Why are there fewer impact craters before the Cambrian period compared to after?

The researchers noted that massive ice sheets during the Snowball Earth event likely scraped away shallower craters. This explains why there are many impact sites from the Cambrian period onward but very few from before that time.

What are some unresolved questions about The Great Unconformity?

One unresolved question is why there are no layers from the time when Earth warmed up, after the glaciation ended. Some scientists suggest the erosion occurred before the Snowball Earth event, potentially triggering the global ice age, but more research is needed.

How might The Great Unconformity be connected to the Cambrian Explosion of life?

Some scientists speculate that the environmental changes caused by the massive erosion might have contributed to the Cambrian Explosion, a period of rapid diversification of life. The erosion could have created shallow seas that were rich in minerals, providing fertile grounds for marine life to flourish.

What is the significance of the researchers' findings in the context of Earth's history?

The findings provide a potential explanation for a significant gap in Earth's geologic record and suggest that the harsh conditions of the Snowball Earth event may have played a role in shaping the biodiversity we see today. However, further research is needed to confirm these connections.

Outlines

00:00

🧊 The Mystery of The Great Unconformity Solved

Geologists have long been puzzled by The Great Unconformity, a phenomenon where the geologic record skips over a billion years. Recent research suggests that massive glaciers during Earth's 'Snowball Earth' period, around 650 million years ago, scraped away over a dozen vertical kilometers of rock, which was then recycled into magma. This new understanding is supported by evidence from zircon crystals and impact craters, showing how glaciers may have caused the erosion that led to this significant gap in Earth's history.

05:01

🌊 The Aftermath of Glacial Erosion and Its Link to the Cambrian Explosion

The new findings might also shed light on the Cambrian Explosion, a period of rapid biodiversity. Scientists suggest that the environmental changes caused by the glaciers' erosion could have contributed to this explosion of life by creating fertile, shallow seas rich in minerals. Although this connection remains speculative, it's a compelling idea that the harsh conditions of 'Snowball Earth' might have been crucial for the evolution of the diverse life forms we see today. The hypothesis is treated with caution, but it offers an intriguing perspective on the interplay between Earth's geology and biology.

Keywords

💡The Great Unconformity

The Great Unconformity is a geological term referring to a significant gap in the geological record, where layers of rock representing over a billion years of Earth's history are missing. This concept is central to the video's theme as it presents a mystery that geologists have been trying to solve for over 150 years. The video discusses a new hypothesis that massive glaciers during the 'Snowball Earth' period could have caused this erosion, removing these rock layers.

💡Snowball Earth

Snowball Earth refers to a hypothesis that suggests Earth was entirely or nearly entirely covered in ice around 650 million years ago. This concept is crucial in the video as it provides a potential explanation for the massive erosion observed in the Great Unconformity. The global glaciation could have caused significant geological changes, including the erosion of rock layers and the deposition of sediments into the ocean.

💡Erosion Hypothesis

The erosion hypothesis posits that the missing rock layers in the Great Unconformity were removed through massive erosion rather than a lack of sediment deposition. The video supports this hypothesis by presenting evidence from the compression of lower rock layers and zircon crystal analysis, suggesting that glaciers scraped away substantial amounts of Earth's crust during Snowball Earth.

💡Zircon Crystals

Zircon crystals are a type of mineral that forms from cooling magma and is very durable, allowing them to survive major geological processes. In the video, scientists use zircon crystals to gather evidence about the conditions of Earth's crust during the period of the Great Unconformity. By analyzing isotopes of uranium, oxygen, and hafnium in these crystals, researchers could deduce that a significant amount of continental crust was eroded and recycled into magma.

💡Subduction

Subduction is a geological process where one tectonic plate moves under another and is recycled into the Earth's mantle. The video mentions subduction as part of the process that could explain the fate of the eroded materials from the Great Unconformity, suggesting that the scraped-away Earth's crust was pulled into the ocean and subsequently subducted, contributing to magma formation.

💡Cambrian Explosion

The Cambrian Explosion refers to a period approximately 541 million years ago when there was a rapid increase in the diversity of life forms on Earth. The video connects this event to the geological changes caused by Snowball Earth, suggesting that the environmental changes and mineral-rich shallow seas created by glacial erosion could have fostered the conditions necessary for this surge in biodiversity.

💡Geologic Record

The geologic record is the history of Earth as documented in its rock layers. In the video, the geologic record's importance is highlighted by discussing how certain layers are missing, particularly those around the time of the Great Unconformity. Understanding the gaps in the geologic record is essential for piecing together Earth's history and the processes that shaped its surface.

💡Impact Craters

Impact craters are depressions on the surface of a planet or moon caused by the collision of a meteorite or other celestial body. In the video, researchers use the presence of impact craters as evidence for Snowball Earth, noting that there are more intact craters after the glaciation period, which aligns with the idea that ice sheets could have scraped away older, shallower craters, further supporting the erosion hypothesis.

💡Oxygen and Hafnium Isotopes

Oxygen and hafnium isotopes are variants of these elements with different numbers of neutrons. The video discusses how scientists analyzed these isotopes in zircon crystals to differentiate between continental and oceanic crust origins. The ratio differences help scientists understand whether the eroded material from the Great Unconformity came from the land or sea, contributing to their understanding of past geological events.

💡Proceedings of the National Academy of Sciences (PNAS)

The Proceedings of the National Academy of Sciences (PNAS) is a prestigious scientific journal that publishes significant research findings. The video mentions that the new study providing evidence for the erosion hypothesis during Snowball Earth was published in PNAS, underscoring the importance and credibility of the research in the scientific community.

Highlights

Geologists have struggled with the mystery of missing time in the geologic record, known as The Great Unconformity.

The Great Unconformity represents a gap of over a billion years in Earth's history, first discovered in the Grand Canyon.

This phenomenon has been identified worldwide, with around ten billion cubic kilometers of Earth's surface mysteriously missing.

Researchers now propose that massive glaciers during the Snowball Earth period scraped away these missing layers.

Evidence from tiny zircon crystals suggests that about 14 vertical kilometers of Earth's crust were eroded and recycled into magma.

Zircon crystals, which can survive major geologic processes, were analyzed for isotopes to trace the origins of this missing material.

The study found that this missing Earth's landmass was likely dumped into the oceans and subducted, supporting the Snowball Earth hypothesis.

The erosion hypothesis is supported by the greater volume of rocks above the unconformity compared to those below.

The research aligns with the theory that the entire planet was covered in ice around 650 million years ago.

Impact craters from the Cambrian period onward are abundant, while those before are rare, suggesting ice sheets erased earlier craters.

The study suggests that the massive glaciation may have set the stage for the Cambrian Explosion, a period of rapid biodiversity.

While the hypothesis is compelling, the study remains cautious as it does not provide direct evidence linking glaciation to the Cambrian Explosion.

The possibility that erosion before the Snowball Earth event triggered the global ice age is also explored.

There are still unresolved questions, such as why certain layers from the warming period after the unconformity are missing.

The research opens up new avenues for understanding the relationship between Earth's extreme past climates and the evolution of life.

Transcripts

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For the last hundred and fifty years or so, geologists have been trying to wrap their heads around the mystery of missing time.

In some places, the geologic record just seems to jump by over billion years, a phenomenon ominously called The Great Unconformity.

But now, a team of researchers may have finally figured out what happened.

In a paper published last week in the Proceedings of the National Academy of Sciences,

they lay out some pretty convincing evidence that massive glaciers ripped away over a dozen vertical kilometers of rock

during a period of Earth’s history many call “Snowball Earth”.

The Great Unconformity is so called because, well, it’s a really big unconformity.

That’s a technical term in geology which refers to places where the aging of rock layers suddenly jumps.

Usually, the slow deposition of sediment from normal wear and tear to rocks leads to layers of rocks that get older as you dig deeper.

But back in 1869, a geologist named John Powell was going through the Grand Canyon and found that over a billion years of geologic record

from just before the diversity of life on Earth exploded was somehow completely missing.

It came to be known as Powell’s Great Unconformity, and soon, geologists discovered it wasn’t isolated to the American Southwest.

In all, we’re talking around ten billion cubic kilometers of earth just… gone.

That much misplaced sediment represents a lot of unaccounted time—almost a quarter of Earth’s history—which makes scientists all the more motivated to uncover what happened.

And there are really only two possibilities: either something made it so basically no new sediment was deposited over those millennia, or there was suddenly massive amounts of erosion which scraped away the geologic record.

So, as geologists do, the researchers looked for evidence of what happened in the rocks above and below the unconformity.

Above the missing layers sits the Tapeats Sandstone, which was forged in the Cambrian period about 525 million years ago,

while below is what’s known as the Vishnu Schist, which is over 1.6 billion years old.

One thing that stands out is how the layers of rocks above have a much greater volume per unit of time than the ones below.

You’d expect the lower layers to be squished since they’ve been under more pressure for longer, but they’re even more squished than they should be.

And that’s more consistent with the erosion hypothesis, as they could have been flattened by the weight of the rocks now missing.

But no one could quite explain where all that removed Earth went.

So, the international research team looked at teeny tiny crystals of a mineral called zircon.

These are among the first solid things to form when molten, liquid rocks, or magma, starts to cool,

and they’re very tough, so they tend to survive major geologic processes that destroy other minerals.

More importantly, they capture the surrounding geochemical conditions when they form.

And scientists can date these crystals by looking at different variants or isotopes of uranium

a radioactive element that decays very, very slowly.

In this study, the team also looked at isotopes of oxygen and hafnium, a silvery metal, in about 30,000 zircon crystals.

The ratios of these are different enough between the continental crust that forms dry land and the oceanic crust that forms the seabed

that it should be clear if either contributed significantly to the magma the crystals came from.

And their results suggested that a whole bunch of the Earth’s land—as much as 14 vertical kilometers—

was dumped into the oceans and then pulled underground and recycled into magma through the process of subduction.

That lines up quite well with the idea that about 650 million years ago, the entire planet, or the majority of it, was covered in ice.

It’s a hypothesis referred to as “Snowball Earth,” and while it was once considered kind of ridiculous, lately, more and more evidence has come to support it.

And the researchers in this study added to that evidence by looking at old impact craters.

They noted that there should be more intact craters after the global glaciation event than before,

as the massive ice sheets would have scraped away shallower craters.

Sure enough, there are plenty of impact sites from the Cambrian onward, but very few from before,

all of which are many kilometers deep.

And combined with the zircon crystal data, they make a strong case that giant glaciers really did scour the earth some 650 million years ago.

There are still a few kinks to be worked out, of course.

One of the biggest is that the Earth would have warmed up millions of years before the unconformity ends,

so it’s not clear why there aren’t layers from that timeframe.

The authors think the ice may have simply left nothing to be eroded, and it took time for new land to form, but more data would be needed to support this claim.

Other scientists think the erosion came before the snowball, and in fact triggered the global winter conditions.

So there’s still more research to be done.

What’s perhaps most intriguing about these findings, though, if true, is how they might explain the explosion of life that came after.

A while ago, some scientists suggested the massive environmental changes from all that erosion might have been responsible for

the huge bump in biodiversity known as the Cambrian Explosion.

And the researchers in this paper note that in addition to adding minerals to the water, the gouges left by the glaciers

could have filled to become fertile, shallow seas where marine life could flourish.

They treat the hypothesis skeptically, of course, as they should, since their study doesn’t provide any direct evidence that it’s true.

But I like it!

On a gut level, there’s just something kind of poetic about the idea that the coldest, harshest winter in Earth’s history may have been essential for the incredible diversity of life we see today to evolve.

Thanks for watching this episode of SciShow News!

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