Did Life on Earth Come from Space?

what if the first genesis of life the abiogenesis is so unlikely that it only happened once in the entire galaxy and that once was not on earth what if primitive life arrived on earth after having traveled vast distances across the Milky Way some scientists think this may be the case this is the panspermia hypothesis there's something odd about the first appearance of life There's something odd about the first appearance of life on earth. The oldest fossils are now dated to only a few hundred million years after the moment earth first became habitable is it really reasonable to imagine that evolution turned an unliving chemical soup into the first true living cells in that geological eyeblink well maybe but it's also possible that life on Earth didn't start on earth at all perhaps it started on a distant world somewhere in the Milky Way and somehow survived a long journey through the void to colonize the early Earth the plausibility of panspermia comes down to whether or not any living organism can survive it's three deadly stages ejection from an origin world traveled to the new world the entry to that world's biosphere let's start with the exciting parts the beginning and the end of the journey one way for a budding microbial astronaut to travel the Stars is via Luther panspermia basically be attached to a rock that travels between planets now we know that debris from planetary surfaces can be ejected into space during asteroid or comet impacts hundreds of meteorites have been found on earth that have compositions suggesting they originated from the Moon or Mars many chunks of Earth have also been ejected into space most of them from the largest impacts like the one that killed the dinosaurs some of that debris would have contained life but could hitchhiking microbes have survived that ejection to escape Earth's gravitational field a chunk of impact debris has to be kicked to a minimum of eleven point two kilometers per second that's the escape velocity at Earth's surface that requires an acceleration of up to hundreds of thousands of GS and hundreds of thousands of Earth atmospheres in shock pressure similar forces apply when it smacks down at the other end of the journey temperatures in these rocks can rise to several hundred Kelvin in the impacts and during reentry that all sounds pretty unsurvivable but scientists have engaged in various forms of microbe abuse to test this this includes shooting high-velocity projectiles loaded with colonies spitting them up in an ultracentrifuge attempting to splat colonies with extreme pressure in back plates and if that's not realistic enough microbe laced rocks have been dropped from space strapped to the outside of reentry vehicles many life forms have been tested from corn bacteria that you find everywhere in the soil to primitive cyanobacteria to heat resistant extremophiles and even fungus spores and lichens while survival rates may be low at least a small fraction of bugs of any of these types can survive the pummeling of high pressure acceleration exposure to extreme temperature for example in atmospheric reentry is more problematic some extremophiles can survive at temperatures above a hundred Celsius but the surfaces of rocks during impact or reentry will be much much hotter than this and this is where we identify our first microbial contender for panspermia endoliths these are organisms that live deep within rocks deep enough that they're protected from the extremes of temperature change as we'll see endoliths are exceptional candidates as micro cosmonauts for a number of reasons they may also be the only critters that can actually survive the journey between planets but before we talk about the hazards of that journey let's look at a gentler mechanism for getting life into space a wide variety of living single-celled organisms are found floating around in the atmosphere as high as the stratosphere some of this material may make it into space just this year Russian cosmonauts reported the discovery of familiar bacterial DNA on the outer surface of the International Space Station they suggested rowed electrical currents from the atmosphere below or it came from space probably the former though these levitating microbes have a gentler journey up and they may also have a faster trip to their destination very small individual bacteria can be accelerated by their star's own radiation and be ejected from the solar system this is Radio panspermia stars may be constantly spraying their germy life through the galaxies in some respects it sounds like levitating into space and becoming your own solar sail is way more efficient than Luthor panspermia except for one thing the vicious environment of space probably annihilates all microbes not surrounded by a nice big spaceship made of rock getting up and down again from space is the fun part but for a budding panspermia life-form the journey itself you simultaneously the most boring and the most lethal our pilgrim microbes have to contend with near absolute zero temperatures extreme dryness a hard vacuum and probably worst of all some incredibly destructive radiation for up to millions of years so can they do it the best way to simulate the conditions of space travel is to send things to space the first experiment was way back in 1936 when fungal spores were sent on a stratospheric balloon ride since then every potential Pants permeating life-form has taken rides on various satellites most notably the International Space Station it's mostly single-celled organisms and spores but also tardigrades and nematodes some of these tests were actually to test survivability on Mars but the results Trane's and in some the results are clear many bugs can survive the vacuum freezing cold microgravity and absolute dryness of space but radiation is a problem we'll come back to that when protected from radiation various bacteria fungi lichens archaea and viruses have been revived after months of exposure to the cold dry microgravity of the vacuum in some cases it's after six years even the tardigrade everyone's favorite extremely philic multicellular teddy bear can revive after exposure to space the key is cryptobiosis many life-forms can enter or produce a hibernating form that's incredibly resistant to adverse conditions in particular life-forms that could survive extreme dryness and hydro biotic life-forms do especially well that includes certain reproductive spores especially of fungi but also critters can enter an N hydro biotic state they dry out shrivel up and wait out the bad conditions tardigrades are an amazing example of this but the real champions are endospores this is a hibernation state that many bacteria enter when deprived of the needful conditions for life they generate a protective wall shrink down stabilize their DNA and essentially shut off all metabolism they don't need water air or nutrients and are remarkably resistant to radiation damage or DNA decay bacterial endospores have been rejuvenated after up to six years exposure to the cold and vacuum of space there are reports of viable endospores found on earth and dated to millions of years perhaps even a couple of hundred million years plenty long enough to make an interstellar journey the real challenge is radiation solar ultraviolet radiation in space can reach a hundred million times the UV intensity of sea level this will typically completely destroy any unprotected microbe in a fraction a second DNA molecular machinery and cell walls are shredded by ultraviolet light tardigrades and bacterial spores are somewhat resistant the latter if they are in layered colonies photosynthetic cells like cyanobacteria and lichens can also survive direct sunlight in low Earth orbit briefly mortality is still high in all of these like and seem to do the best with cell surviving up to several months of exposure but probably not for years a star's intense UV radiation probably rules out radio panspermia only the tiniest microbes probably bacterial spores are light enough to be accelerated by a star's light and those things are likely destroyed before they can get far enough from their home star anyway even far from the intense UV radiation of a star interstellar space is thick with energetic cosmic rays near light speed atomic nuclei as well as x-rays and gamma rays endospores are somewhat resistant to cosmic rays but there is a limit the only true protection is a thick wall of solid material once again we're back to impact ejecta and litho panspermia microbes buried deep enough in rock are entirely safe from UV and safe from cosmic rays if deep enough endoliths natural rock dwelling organisms have representatives in all domains of The Tree of Life they are often extremophiles and their resilience often translates to the conditions of space they also have exceptionally low metabolisms with some having reproduction rates of decades to centuries or perhaps even millions of years there are endo lytic bacteria viruses and fungi dug out from deep beneath the ocean floor that appear to be a couple hundred million years old if anything can travel between the stars it's these guys okay to review many microbial life forms can survive the journey into and out of space endoliths can survive long space journeys buried in rock can they really make it to another planet and is it ever likely to happen I mean statistically let's start with the easy journey within a solar system like Mars to earth the minimum travel time for a Martian impact ejector to get to earth is something like six months although it's more likely to take years or centuries given the random nature of the journey those timescales are totally reasonable for the more hearty earth microbes traveling between solar systems is a whole different game first the rock has to escape not just from the planets gravitational field but its stars field also to get a microbe from the surface of the earth to interstellar space requires a large velocity around four times what is needed to just escape the earth that rock would endure a commensurately higher acceleration to attain that speed with all the pressure and temperature pain that went with it once an infested Rock makes it out of the solar system it has a very long very boring journey ahead to get to the nearest stars a rock traveling at the sun's galactic orbital speed of 30 km/s would take several tens of thousands of years but real panspermia expeditions likely take much longer there's only a tiny chance that an interstellar rock will be caught in the gravitational field of any given star that it passes take uma or more for example the asteroid that zipped through our solar system in 2017 it's going to escape our solar system and this was probably the closest encounter it had for hundreds of millions of years some life-forms may be able to hibernate that long but at this point the issue is just frequency of impacts is it at all likely that a microbe bearing rock from another star system hit the earth in the short time it took life to take hold well it depends on the abundance of life in the galaxy but it seems dubious one interesting alternative possibility is that life bearing rocks aren't so often captured by planetary systems but rather by the giant deceived and gas that precede the formation of planets circled protoplanetary disks these could act like gigantic nets to capture break apart and disperse the seeds of life before a solar system even forms star fairy microbes could then remain in hibernation into a planets coalesce from the protoplanetary disk and one of these life bearing rocks slams into a newly habitable world perhaps the most convincing argument against panspermia is that if the dormant seeds of life are so common throughout the galaxy why haven't many of the forty billion earth-like planets produced technological civilizations far in advance of us and speaking of aliens a fun version of this idea is directed panspermia in which the seeds of life are sent out deliberately to engineer life across the galaxy they would actually be pretty easy for a moderately advanced civilization but aliens aside panspermia is a plausible but by no means accepted explanation for the origin of life on Earth if it's true then you me and everyone you know is an alien a genetic immigrant from another world perhaps with many cousins scattered across the galactic reaches of space time before we get to comments I am very pleased to announce today's episode is brought to you by our brand new space-time merch store we have all new nerd tastic t-shirts mugs hats posters and even a baby onesie we'll be updating the store with even more merchants coming weeks so make sure you check out PBS space time comm in the last episode we talked about the interstellar space rock boom or more and the proposition by some astronomers that it may be an alien light sail I laid out the case why this is very unlikely and I asked you guys what you thought about the out waited attention the media gives to these sorts of Fringe ideas regardless of their connection to reality is it harmful or is any public exposure to science good it seems that you did think about it and quite hard justin o'brien places the responsibility on the media stating the problem is the rampant lack of journalistic integrity that problem exists wherever a journalist is looking for fame and its trappings and when a media is slave to advertiser demands well this is definitely a factor when both the media outlet and the writer live or die by that month's clicks it's easier to lose sight of old-fashioned journalism or to make the necessary sacrifices to pay the rent hmm hard to say whose fault that is advertisers editors journalists mindless market forces or the viewer for insisting on free content which brings us back to advertisers guest who puts it well and I quote when the media says Harvard scientist says X this is received effectively as a pronouncement of truth from scientists when it is inevitably proven false or the predicted thing doesn't eventuate the public naturally learns not to trust in science as a whole even casting doubt on all established science as well Ian Oksana made similar points also adding that it's harmful of scientists or communicators do not qualify their fringe ideas with notes of caution otherwise it gives the public a distorted view of how science works and a related point Steve Zara says that exaggerations and hype are harmful because they encourage excitement about the wrong things Sam Winfield agrees saying that hype over nothing leads directly to disinterest they are crying wolf all good points if the press only emphasizes the most outlandish interpretations do we eventually get bored by the real universe give kids too much candy and they won't eat their vegetables in this case umemura is totally amazing as our first natural interstellar visitor and the glory belongs to those who discovered and unlocked its real properties seems a bit cheap for someone to come swooping in and shout aliens every time something inexplicable is observed and we have at least one counterpoint mark gibble says that no it's probably not harmful at least in this case as long as we have people to bring rationality to the dreamers and the skeptics alike it's a proud Duty we have here at PBS space time squashing dreams and killing the buzz since 2015 heartbreak one changes the subject pointing out that if aliens were to land on PBS studios we would do a lot of biological testing and determine that most probably it isn't aliens wait are you disparaging our ability to biologically test aliens or are you saying we'd lie about it if we found out that there were aliens I assure you I will be the first on the alien bandwagon and when the evidence is clear so you know how to be sure Italians no fun buzzkill skeptics like us will be saying it too although a few of you point out that denying that the murmur is aliens is just what aliens would say, or go we are aliens well to deny that would make me even more of an alien so I guess you got me

Channel: PBS Space Time

Views: 654,988

Keywords: life, earth, aliens, panspermia, seed, dna, planet, solar system, pbs, space time, spread, science, fossil, chemical, pbs spacetime, Matt O'Dowd, astrophyics, pyhiscs, physics, astrobiology, merch

Id: REl20rlZGTw

Length: 18min 33sec (1113 seconds)

Published: Thu Dec 06 2018

Reddit Comments

[u/alzee76]

Tuning in to see Matt wearing a firefly shirt while wearing your own firefly shirt is part of what makes life worth living.

[u/drinks2muchcoffee]

Forget loop quantum gravity, I’m worried Matt is never even going to finish string theory

[u/wildseyed]

Given the news this past week about the discovery of clays on Bennu by OSIRIS-REx, and the demonstrations by Harvard researchers a while back on the role clay might have played in the formation of the first living cells, I think the possibility of panspermia being a viable propagator for life is increased. Especially if the lump of clay can act as an ablative heat shield.

[u/[deleted]]

Ive lately been thinking that the whole LUCA thing coupled with the fact that life arose super readily as Earth cooled does imply some fuckery.

Shadow biology being absent is a serious problem if we go off the assumption that abiogenisis is easy and common.

Thats doesnt nescesarily imply seeding from afar, but it does suggest the current theory is murky at best.