JASMA

Here’s a sentence you didn’t expect to read today: parts of Earth might be “extraterrestrial blobs.”
Not as in “aliens built the pyramids” (please no), but as in “your planet may be quietly wearing
leftovers from the ancient crash that made the Moon.”

The idea making headlines is this: as much as ~2% of Earth’s mass could be material
from Theiaa Mars-size world that likely slammed into early Earth about 4.5 billion years ago,
kicking up the debris that became our Moon. The twist is where that material might be hiding:
deep in the mantle, gathered into two gigantic, weird regions near the core.

What the “2% debris” claim actually means (and what it doesn’t)

“2% of Earth” doesn’t mean your backyard is 2% moon dust. It’s not about the crust where we live
and argue about parking. The claim is about the deep mantlethe layer of hot rock
between Earth’s crust and corewhere scientists have long detected two massive anomalies.
Some recent modeling suggests those anomalies could be made of denser, iron-enriched impactor
materialpossible remnants of Theiaadding up to around two percent of Earth’s mass.

The important word in the headline is may. This is not a “we dug it up” situation.
It’s a “the best simulations and seismic observations are starting to line up” situation.
Think of it as a compelling suspect in a very old cosmic cold case.

Quick rewind: the Moon’s origin in one espresso shot

Earth’s early neighborhood was basically bumper cars, but with lava and existential consequences.
The leading explanation for the Moon’s origin is the giant impact hypothesis:
a large body (often nicknamed Theia) collided with young Earth, and the impact flung molten and
vaporized material into orbit. That orbiting debris eventually clumped together into the Moon.

Why do scientists like this idea? Because Moon rocks brought back by Apollo missions strongly
suggest the Moon formed from an intensely energetic event: the samples point to a very hot,
once-molten Moon and a history consistent with massive heating and volatile loss.
In other words, the Moon looks like something that was born from violence, not gentle adoption.

But there’s a snag: the Earth and Moon are weirdly similar in many isotopic fingerprints.
If two independent worlds crashed, you’d expect the Moon to look more “mixed” and less “matching.”
That puzzle has pushed researchers to explore different impact angles, energies, and mixing physics
for decadesand it’s part of why deep-Earth leftovers (like those mantle blobs) are so intriguing.

Meet the deep-mantle “blobs” that sparked the whole debate

What are LLVPs/LLSVPs?

Deep down near the boundary between Earth’s mantle and core, seismic imaging has revealed
two enormous regions where seismic waves slow down. They’re commonly called
large low-velocity provinces (LLVPs) or large low-shear-velocity provinces
(LLSVPs). Same idea, slightly different naming habitslike “soda” versus “pop,” except
nobody throws a fit at Thanksgiving.

These structures are continent-sized, and they sit far below the surfacecloser to the core
than anything you’ve ever stressed about. One is generally described as lying beneath Africa,
and the other beneath the Pacific. Scientists have known they exist since seismic studies in the late
20th century, but their origin has been debated for years.

Why they’re weird

“Low velocity” means seismic waves pass through them more slowly than through surrounding mantle.
That can happen if the region is hotter, partially molten, compositionally different, denseror some
chaotic combination. Many hypotheses have competed here:
recycled oceanic crust “graveyards,” ancient magma ocean leftovers, and now (re-entering the ring)
impactor remnants from the Moon-forming collision.

How could a Moon-making crash leave souvenirs inside Earth?

The key is density and incomplete mixing.
In a giant impact, you don’t just get a debris disk. You also massively disturb Earth’s interior:
rock melts, flows, stratifies, and convects. If the impactor’s mantle was more iron-rich than
Earth’s mantle, that material could have been intrinsically denser, giving it a tendency to sink
and accumulate near the core-mantle boundary.

For a long time, a common assumption was: “Surely billions of years of mantle convection would
stir everything into a smooth soup.” Newer work pushes back on that simplicity. Convection mixes,
but it doesn’t guarantee perfect homogenizationespecially if you’re mixing materials with different
densities and if some of that material can collect into stable, large-scale piles at depth.

That’s how you get a plausible storyline: Theia hits Earth → the Moon forms from orbiting debris →
some Theia material ends up inside Earth → the densest parts sink and survive as deep mantle anomalies.
Cosmic drama, with a very long after-credit scene.

Why researchers think the blobs could be Theia (and not just “old crust parking”)

No single observation shouts “I am Theia’s mantle, hello.” Instead, this hypothesis stacks multiple
clues that might point the same direction:

• Location and scale: The anomalies are gigantic and sit at the core-mantle boundary, where dense
  material can plausibly accumulate and persist.
• Composition hints: Some interpretations suggest unusually high iron content, which fits the idea
  of denser impactor mantle fragments.
• Modeling match: Advanced simulations show impactor mantle material can survive, sink,
  and concentrate in the deep mantle in amounts that could be large enough to matter.
• Earth history connection: If these structures are ancient, they could have influenced early mantle
  dynamics, hotspots, and even the onset of large-scale tectonic behavior.

Meanwhile, non-Theia explanations still have real traction. Subducted slabs and recycled crust are
observed parts of Earth’s mantle story, and some scientists argue LLVPs could be largely built from
that recycled material. The point is: the “Theia blobs” idea is promising, not settled.

The 2% number: where it comes from and why it’s still a “may”

Simulations (great) are not samples (greater)

The “about 2%” estimate comes from high-resolution modeling of Moon-forming impact scenarios,
where researchers track how impactor material mixes, stratifies, and potentially sinks into the deep mantle.
Depending on impact conditionsangle, speed, the bodies’ internal structures, and how turbulence is handled
numericallymodels can produce different amounts and distributions of surviving impactor mantle.

That’s why the claim is framed probabilistically. It’s not “we measured 2% with a cosmic tape measure.”
It’s “if these assumptions are close to reality, the leftover impactor mass in the deep mantle
could plausibly be on the order of a couple percent.”

Putting 2% into human terms (because your brain deserves kindness)

Earth is massive. Two percent of Earth’s mass is still an outrageous amount of materialon the order
of more than a Moon’s mass. The point isn’t that Earth is “2% alien” in some uniform, fun-size way.
The claim is that Theia’s remnants could be concentrated into deep mantle reservoirslike two
planet-scale storage units you can’t access without a drill made of science fiction.

Does this help explain why Earth and the Moon look so similar?

It can, at least partially. One major constraint on any Moon-formation scenario is the
Earth–Moon isotopic similarity in multiple elements. Some studies have argued this points to
extremely thorough mixing during the impact, potentially including high-energy or head-on
impact geometries. That mixing would blend Theia and proto-Earth material so tightly that the Moon
and Earth end up looking like close relativesbecause they literally became one messy family.

The “Theia-in-the-mantle” idea plays nicely with a world where mixing is strong but not perfect:
you can have enough blending to make Earth and Moon similar in many tracers, while still leaving
behind some distinct, denser impactor-rich material that sinks and survives at depth.

And the debate keeps evolving. New isotope work continues to refine how “identical” Earth and Moon
truly are, how representative Apollo samples are of the whole Moon, and what that implies about
impact conditions and source regions in the early inner solar system.

Why this matters beyond being a killer trivia fact

1) Earth’s interior might still carry the blueprint of its origin story

If deep mantle structures really contain impactor remnants, then Earth isn’t just a planet that
experienced the Moon-forming eventEarth is a planet that still records it internally.
That would be remarkable, because the mantle is dynamic, hot, and constantly on the move.
A surviving “impact signature” would tell us something fundamental about how long chemical
heterogeneities can persist inside rocky planets.

2) Mantle plumes, hotspots, and the long-term personality of Earth

LLVPs are often discussed alongside mantle plumesupwellings that can feed hotspot volcanism.
If those deep anomalies help anchor or influence plume formation, then whatever they’re made of
could shape patterns of volcanism over geologic time. In that sense, Theia’s leftovers (if real)
wouldn’t just be a historical artifact; they’d be part of Earth’s ongoing internal engine.

3) The “proto-Earth might not be fully erased” twist

A separate but related thread of research suggests that some very ancient chemical signatures
potentially predating the Moon-forming impactmay still survive in certain Earth rocks.
If true, it reinforces the idea that Earth’s interior can preserve deep-time anomalies longer
than we once assumed. Put differently: the early Earth may have been more like a layered lasagna
than a perfectly blended smoothie.

What would make scientists more confident (or change their minds)?

This hypothesis lives at the intersection of seismic imaging, high-pressure mineral physics,
isotope geochemistry, and impact modeling. The most convincing progress would likely come from
multiple lines converging:

• Sharper seismic constraints: better mapping of LLVP boundaries, thickness, and internal structure.
• Material property tests: laboratory and computational work on how iron-rich mantle compositions
  behave at core-mantle boundary pressures and temperatures.
• Geochemical “fingerprints”: linking hotspot basalts or deep mantle-derived rocks to predicted
  impactor-like signatures (without forcing the data to confess).
• More lunar samples: broader sampling beyond Apollo landing sites could reveal how uniform
  (or not) the Moon is, tightening constraints on mixing during formation.

The big takeaway is not “case closed,” but “the case is getting interesting.” A couple decades ago,
the idea that an ancient impactor might still be inside Earth would’ve sounded like sci-fi.
Today, it’s a testable scientific hypothesis with credible modeling and observational context.

The bottom line

The claim that “2% of Earth may be debris from the collision that formed the Moon” is a bold
way of summarizing a nuanced idea: Earth’s deep mantle contains two enormous anomalies, and
new research suggests those structures could be surviving fragments of Theia’s mantlematerial
left behind by the Moon-forming impact and stored near the core for billions of years.

Whether the number is exactly 2%, smaller, larger, or ultimately not Theia at all, the bigger story
is thrilling: Earth might still contain physical echoes of the event that gave us night tides,
eclipses, and a Moon that has inspired humans to write poetry, invent calendars, and occasionally
trip over their own telescopes.

Experience: Make the Moon-Forming Impact Feel Personal (and a Little Less Like a Textbook)

Big numbers like “4.5 billion years” and “2% of Earth’s mass” can make your brain quietly exit the room.
So here are some ways to experience this story in human-scale momentsno PhD required, and
no mantle drill bits will be harmed in the process.

1) Do the “Moon Reality Check” the next time you see it

Next clear night, step outside and actually look at the Moon for a full minute. Not a glance.
Not a “yup, still there.” A real look. Notice how bright it is, how the shadows carve out craters,
and how the light feels oddly “clean.” Then remember: this whole object may be the child of a
planet-scale crashand Earth might still be storing some of the other parent’s material deep below you.
Suddenly the Moon isn’t just “the thing that ruins astrophotography when it’s full.” It’s an artifact
of planetary formation still influencing oceans, climate rhythms, and life’s timetable.

2) Visit a museum exhibit and treat it like time travel

If you can get to a natural history museum, a science center, or a space exhibit with lunar material
(or even meteorites), go. The “experience” isn’t just the rockit’s the mental jump:
a small sample can connect you to an era when Earth was molten, impacts were routine,
and a single collision reshaped our planet. Read the placards like they’re clues in a mystery:
“volatile depletion,” “magma ocean,” “isotopes.” It’s basically forensic scienceexcept the crime
scene is 4.5 billion years old and the suspect is a planet.

3) Try a tabletop analogy for sinking “dense blobs”

Want an intuitive feel for why impactor material might end up parked at the bottom of the mantle?
Here’s a harmless analogy: fill a clear glass with a thick liquid (like syrup) and gently add a denser
liquid (like honey) along the side. Even if you swirl a bit, the denser stuff tends to sink and pool.
Now scale that up to a planet with hot, convecting rock and compositional differencesand you get the
basic logic behind “dense material can survive as deep reservoirs.” Is it a perfect physical model?
Absolutely not. Is it a satisfying “ohhhh, I get the idea” moment? Yes, and your brain deserves that.

4) Watch the Moon’s phases for one full month (seriously)

Track the Moon nightly for one lunar monthphotos, notes, or just quick sketches.
This is the easiest way to experience how the Moon locks itself into your daily life:
the changing light, the timing, the way it moves relative to the background stars.
Then layer the origin story back on top: the Moon may be made from material ejected in a catastrophe,
and Earth might contain leftover impactor mantle material that’s still influencing deep Earth dynamics.
Suddenly your phase tracker isn’t just “cute”it’s a connection to planetary evolution.

5) Do the “two-blobs underfoot” thought experiment

The next time you’re on a map app, zoom out until you can see Africa and the Pacific.
Now imagine two vast regions deep below those areasstructures so large they make continents look like
decals, sitting near the core-mantle boundary. Scientists infer them from how seismic waves travel
through Earth. You can’t see them, you can’t touch them, but they’re part of Earth’s internal architecture.
If those structures are Theia remnants, then Earth didn’t just swallow a planetit kept a couple of
enormous “souvenir piles” for billions of years. That’s the kind of mental image that makes geology
feel less like memorizing layers and more like reading an epic novel written in pressure and time.

6) Turn the headline into a conversation starter, not a “gotcha”

The best experience might be social: bring the idea up with a friend and see where the questions go.
“If Earth has Theia inside it, could other planets have similar leftovers?”
“Would Venus have its own ‘blobs’?”
“Does this change how we think about plate tectonics starting up?”
You don’t need to pretend certainty. The fun is in the curiosity:
science is a process, and this is a hypothesis with real momentumnot a final answer.
That’s not a weakness; that’s the whole point.

If you do any of these, the story stops being a distant cosmic headline and becomes something you can
feel: the Moon overhead, Earth underfoot, and a collision in the deep past that still might be shaping
the planet you live on. Also, you will never look at the phrase “extraterrestrial blobs” the same way again.