Did you know that many of us have up to  4% neanderthal DNA?

And that 100% of your   DNA may come from outer space?

No joke.

At least the  biochemistry that defined the coding system   of your DNA may have happened off-world,  and perhaps even long before Earth existed.

Life is the coolest thing to have happened in our  universe.

It would be nice to know if it happened   anywhere else besides Earth—if nothing else to  know just how badly we’re screwing up as we flirt   with self-extinction.

But not only have we never  found credible evidence of life on or from other   worlds, we only have the sketchiest of ideas of  how it began on Earth.

Makes it pretty difficult   to say much about what’s happening out there.

But one encouraging detail is just how quickly   life got started on Earth.

The earliest  fossils are dated to within a few hundred   million years of the Earth first cooling  from its early molten hell-ball phase.

And   if you believe some of the more tentative  biosignatures, it could be much earlier.

In fact, life got started so quickly on Earth  that some have argued that natural selection   just didn’t have the time to take raw elements  all the way to the first single-celled lifeform.

This difficulty led some scientists to  propose panspermia— the idea that life   did not start on Earth at all, but  rather traveled here in the form of   extremely simple and presumably extremely  robust simple organisms.

It’s a fun story,   and we’ve talked about it before, but it’s  not supported by evidence and generally   not considered particularly likely.

But there is a middle road.

Perhaps life didn’t  start in space, but maybe its building blocks   did.

Pseudo-panspermia is the idea that many of  the complex molecules critical for abiogenesis—the   formation of life—were not formed on Earth, but  rather in the depths of space, in some cases   long before the formation of itself.

If these  rained down on our planet in its early years,   that would allow our molecular ancestors to  skip many steps in their path to the first cell.

The evidence for pseudo-panspermia   is rather strong.

And the most compelling  of that evidence is just in, with the safe   return of the OSIRIS-REx mission.

But before we  get to those results, let's review what little we know about the first formation of life.

Life as we know it is based on a  complex interplay of organic molecules,   primarily nucleic acids, proteins,  lipids, and carbohydrates.

In your body,   these work together to form the intricate  machinery of the modern eukaryotic cell.

Of course, the first life was much simpler,  and life’s precursor simpler still—for example,   self-replicating RNA molecules of the RNA-world  hypothesis.

But how did a bunch of non-living   chemicals even get to something as complex  as RNA?

Extremely broadly, assume that in   some energy and chemical-rich primordial  soup, where simple elements combined into organic   molecules, when then combined and recombined in  a chain of trial and error until this natural   laboratory first stumbled on self-catalyzing  and then self-replicating molecules.

The step from organic molecules to complex,  self-replicating RNA is still pretty mysterious,   even if there have been recent advances.

But  the pre-RNA part of the story?

We’ve know that’s   possible for decades.

Back in 1952, a pair of  scientists attempted to replicate the conditions   of the early Earth, with liquid water “ocean”  evaporating into an atmosphere of hydrogen,   methane and ammonia.

An electrical spark  simulated primordial lightning powering   a chain or reactions that ultimately  led to a variety of organic compounds,   including five amino acids—the building  blocks of proteins.

This was the famous   Miller-Urey experiment, and it was our first  hint at how the seeds of life may have formed.

That experiment has now been repeated in  a variety of ways, and we now know that   amino acids can spontaneously form given the  right raw materials, an aqueous environment,   and an energy gradient.

The apparent ease with  which amino acids form led scientists to wonder   just how ubiquitous these organic molecules  might be, not just on Earth, but through the   universe.

For example, in the chunks of rock  and ice that rained down on the early Earth,   first building our planet and then perhaps  seeding it with the precursors to life.

One of the first pieces of evidence  that space rocks are packed with organic   compounds was the Murchison meteorite,  which fell in Australia in 1969.

This is   a carbonaceous chondrite meteorite, so,  made mostly of carbon, clay minerals,   and water.

But it was also found to  contain over 90 different amino acids,   including some that are not commonly found  on Earth, as well as the nucleobases purine   and pyrimidine which are critical components  of DNA and RNA, and other organic compounds.

Carbon dating estimates that Murchison  is around 7 billion years old,   so a couple of billion years older than  even the Sun, meaning that complex organic   chemistry would have been occurring in  space long before life emerged on Earth.

It’s hard to be 100% certain about the origin of  the molecules found in the Murchison meteorite   because the rock was in contact with Earth, which  we already know is infested with life.

However,   the amino acids in the meteorite had one  distinct difference to those typically   found on Earth—they came in both left- and  right-handed varieties—both chiralities,   both mirror reflections.

But all amino acids  produced by Earth life are left-handed—a chirality   that has been locked in since the first common  DNA or RNA ancestor of all life won that great   molecular war 3.5 to 4 billion years ago.

The  presence of both chiralities in the Murchison   meteor tells us that these amino acids have an  abiotic origin—supporing their pre-life formation.

Pretty convincing, but the best way to be sure there’s no cross   contamination from Earthly life is  to get samples directly from space.

And there have been some incredible efforts to do  this.

NASA’s stardust mission collected samples   from the coma of comet Wild 2 and returned them  to Earth.

The Japan Space Agency was the first to   land on an asteroid and return samples—twice,  actually with Hayabusa and Hayabusa2.

And ESA’s   Rosetta mission was the first to send a lander  to a comet where it analyzed samples on location.

These and other missions have shown that  organic compounds are abundant on space rocks.

But how far along can this pre-biotic  biochemistry really advance in space?

How much   of a head start might pseudo-panspermia have given to  life on Earth?

Some of that has now been answered   by NASA’s OSIRIS-REx mission.

In our long tradition  of unwieldy science acronyms, this stands   for Origins, Spectral Interpretation, Resource  Identification, and Security-Regolith Explorer.

The spacecraft launched in 2016, with the goal  of landing and target was an asteroid by the   name Bennu.

Bennu is a pretty ordinary  carbonaceous asteroid of middling size,   at around 500 m in diameter.

It’s part of the  Apollo group—a collection of more than 20,000   asteroids with orbits that cross Earth’s.

That means they do sometimes slam into   our planet—like the one that exploded over  Chelyabinsk in 2013.

Or as in 2024 YR4, which   has a miniscule chance of hitting Earth in 2032.

Bennu has no immediate chance of hitting us, but   it does make a close approach to Earth of around  300,000 km or 24 Earth diameters every 6 years.

The upside of these potentially cataclysmic  neighbors is that they’re quite easy to visit.

Which OSIRIS-REx did.

It started that journey  in orbiting around the Earth, followed by a   mad dash to catch up to and orbit the asteroid.

After a few years of observation and analysis,   a suitable landing site was identified and the  spacecraft touched down.

Samples were collected   before an easy escape from Bennu’s frankly  pathetic excuse for a gravitational field.

OSIRIS-REx rejoined Earth’s solar orbit  and dropped its sample capsule into our   atmosphere in September of 2023.

And after  all of that, the capsule’s parachute failed.

Its first parachute.

The second opened  just fine and the capsule landed right   on target in Utah.

Since then, scientists  have been hard at work analyzing the sample,   and the first results of the findings were  finally published in January this year.

So, what did we find?

Among the most  exciting discoveries in the sample   are all five of the nucleobases  that serve as the code for DNA and   RNA.

This is the first time we’ve found   five on the same space rock.

The samples  also contained 14 of the 20 amino acids   that life on Earth harnesses to make proteins, These amino acids have both left- and right-handed   chirality, just like the Murchison molecules.

Bennu sample has various other interesting   compounds, including a surprising richness  of ammonia—12 times higher than in the   Murchinson meteorite.

Curiously, Bennu orbits  too close to the sun to preserve pure ammonia,   so its richness hints at a colder, more  distant origin.

But more on that later.

One of the most exciting finds were 11 different  minerals that we know form when brines slowly   evaporate.

That means Bennu, or the stuff  that formed it, was once in an aqueous,   salty environment.

In fact, there were many signs  of the role of water in Bennu’s formation.

Its   minerals match most water-altered meteorites ever  found on Earth, as well as the samples collected   from asteroid by JAXA.

But, unlike most meteorite  samples, Bennu contains sodium rich salts,   which are rare in meteorites.

Similar salts  are found here on Earth, like in Searles Lake,   California, confirming that Bennu once  contained pockets of sodium rich water.

But normally we don’t find sodium rich salts  in meteorites because they react strongly   with our atmosphere.

But because Bennu’s  samples were stored in pure nitrogen,   they maintained a pristine  suite of salts for analysis.

With this analysis in, we’re able to  reconstruct a likely origin story for   this asteroid.

And that origin is  probably a water-rich world that   existed for a time in the early solar  system, but has since been destroyed.

Let me take you back 4.5 billion years ago, on the icy fringes of the early solar system beyond Jupiter’s orbit,   a distant protoplanet formed from a mixture of  rock, metal, and frozen water.

As radioactive   elements created in an ancient supernova decayed  within, heat melted some of the ice, creating   mineral-rich reservoirs.

These ancient waters  interact with ammonia and formaldehyde, sparking   the formation of complex organic molecules.

When the water eventually evaporates, it leaves   behind veins of brine-sourced minerals.

This protoplanet, however, is doomed.

Before it   can grow to full planet-hood, a catastrophic  collision—perhaps with another similar   body—scattering its fragments into space.

And  Bennu and many other asteroids pulled themselves   together from this debris.

In the unsettled  early solar system with its wandering gas giants,   Bennu’s orbit was also fated to wander.

Eventually  it settles into an orbit perilously close to an   inner-solar system planet.

A planet that  would slowly turn blue-green and then   twinkle with night lights and then send a tiny  visitor of metal and silicon named OSIRIS-REx.

At least, it seems like this is the most likely story  based on the bits of Bennu that we brought   back home.

And if Bennu has the variety  of organic compounds that we discovered,   so do many asteroids, and probably comets.

Many of these peppered the early Earth—far   more than today.

In fact, they are  kind of what Earth is made of.

Like I said,   pseudo-panspermia—the idea that the chemistry  of life got a head start from space molecules—is   pretty well supported these days.

But does this tell us anything about   the likelihood of life elsewhere?

We can be  pretty sure that there are watery worlds out   there that started out with an abundance of  organic compounds, all the way up to amino   acids and even nucleotides.

It’s becoming harder  to imagine that simple life doesn’t form in lots   of places.

But the observation  of DNA and RNA coding nucleobases could tell us   something pretty profound.

If all planets start  with a similar chemical cocktail, maybe there’s   a pretty narrow path to life everywhere—one  that involves DNA-like molecules.

Maybe the   system that codes Earth life—including your own  DNA—was set by extraterrestrial biochemistry.

And what about OSIRIS-REx?

It delivered  its sample, but it stayed out there   to continue its adventure.

NASA has renamed in  OSIRIS-APEX, and it’s now preparing to intercept   the asteroid Apophis.

This time the mission  isn’t primarily to discover the origin of life,   but to help prevent its annihilation.

Apophis  is one of the most hazardous Apollo asteroids,   and has a miniscule chance of hitting Earth  in 2036.

OSIRIS-APEX will study any changes   to the asteroid that occur during its close  encounter with Earth in 2029.

This will help us   track Apophis more precisely.

It’ll also teach  us more about these close encounters, perhaps   allowing us to avert a future giant impact.

Thanks for looking out for us, little buddy,   and for helping us seek our chemical origins in  a protoplanetary, perhaps pre-solar spacetime.