Presentation on theme: "Where Did We Come From? Might WE Be Aliens? Richard Boyd."— Presentation transcript:
Where Did We Come From? Might WE Be Aliens? Richard Boyd
Brief Outline A couple of definitions, both biological and astronomical How did the molecules of life get to Earth? Meteorites Evolving from the basic molecules of life to critters How will life on Earth end? Do aliens exist?
What Constitutes a Religion? Religions answer 3 basic questions: Where did we come from? Why are we here? Where are we destined to go? From J. Gordon Melton.
Molecules of Life: What ARE They? Nucleobases: Our DNA (deoxyribonucleic acid) and RNA are composed of nucleobases, which are “simple” molecules that are assembled to form the DNA and RNA, which are complex molecules. Five nucleobases: adenine, guanine, cytosine, thymine, and uracil. NUCLEOBASES = DNA/RNA = WHAT AND WHO WE ARE. Amino Acids: We need about 20 of these; they get combined in our cells to make the proteins that are the machinery of our cells. There are more than 200 known amino acids. AMINO ACIDS = PROTEINS = MACHINES BUT FIRST WE NEED ELEMENTS!
A section of DNA
The Electromagnetic Spectrum The electromagnetic spectrum Photon: a “particle” of EM radiation Wavelength: the distance, in x, over which a wave, or an oscillation, repeats itself X
Why the Different “Colors”? Different “colors,” or wavelengths, come from different atoms, so the colors (but not FALSE colors) tell you what atoms are in each region of the nebula. Astronomers use “spectrographs” to analyze the colors (or wavelengths) coming from a star to see what it contains. These are similar to using a glass wedge to analyze the light from the sun streaming through the window.
An Optical (Absorption) Spectrum
Do All Stars Exhibit Evidence of Hydrogen, Iron, Carbon, Oxygen, Magnesium and Other Elements? NO! Some stars have very few elements other than the hydrogen and helium that came from the Big Bang. The abundances of the heavier elements build up as time proceeds, and massive stars explode to seed the galaxy with newly synthesized nuclei. Then the Galaxy mixes all this stuff. Astronomers have established all these facts beyond a doubt.
Getting from Elements to Molecules New stars are made from the Galactic stuff, and planets are also formed around the stars, made from the same Galactic stuff. Simple molecules can be made either in the cosmos from the oxygen, hydrogen, carbon, silicon, etc. made by the stars, or on Earth. Water, methane, carbon monoxide, hydrogen cyanide, and lots of other molecules fall into this category. How do we get from these to the somewhat more complex molecules of life??
Making the Molecules of Life Out of These Simple Molecules Stanley Miller and Harold Urey, in the 1950s, combined simple molecules in a test beaker and imposed a spark. They found they could make many amino acids in this way! The simple molecules were likely present in the environment of early Earth, so all one needs is some lightning, and one has at least the amino acids. This has been the textbook description for decades of how the molecules of life were formed.
But There Are Issues … This explanation doesn’t tell how the nucleobases got formed: they aren’t made from the amino acids. And, the amino acids have “handedness.” If produced in the lightning storm you would have equal numbers of left- and right-handed molecules. But on Earth the amino acids are virtually ALL left-handed. It’s not easy (possible?) to see how the amino acids from the lightning storm all got to be left- handed!
How Do the Molecules Form in Space? Dust grains form in the nebulae like the one on the previous slide. This is also well established; indeed the dust obscures some of the things astronomers would like to see! The dust grains allow elements to get together to form molecules. Astronomers have identified many simple ones, e.g., carbon monoxide, water, methane, alcohol (!), etc. And there are many others: Polycyclic Aromatic Hydrocarbons, PAHs! Some of these PAHs may be amino acids.
What About the Molecules of Life? There isn’t any lightning in outer space. Can the molecules of life, the amino acids and the nucleobases, form there? These would be harder for astronomers to identify, as they are more complex, and they don’t have such characteristic color (wavelength) signatures as simple molecules. PAHs! Also, the more complex the molecule, generally the less abundant it is in the cosmos. So even if they are there, you wouldn’t expect many of them, so their spectral signatures would be faint.
But the Molecules of Life ARE Made in Outer Space On 28 September 1969 at 10:58 AM, near the town of Murchison, Victoria, Australia, a fireball was observed to separate into three fragments before hitting Earth. Many fragments were found over an area larger than 13 km², with individual masses up to 7 kg. The total collected mass exceeded 100 kg. The Murchison Meteorite contained more than 70 amino acids; they ARE made in outer space.
So might the Molecules of Life be made in Outer Space, then delivered to Earth via Cosmic Stork? Several more meteorites have been found that were also found to contain amino acids. These don’t happen frequently, but they aren’t rare events.
Yeah, right! Might the samples have been contaminated? OK, so look for amino acids in the meteorites that are not naturally occurring on Earth (there are more than 200 of them, most are NOT naturally occurring). They found many of them. Nucleobases were also found, but at much lower abundance. But it looks like they also came from outer space.
But Does Making the Molecules of Life in the Cosmos Have Advantages Over Making Them in an Earthly Lightning Storm? Actually, YES! Some of the meteoritic amino acids have been observed to be left-handed, as are the Earthly ones. None of them has been found to be right-handed. But, the fraction of them that has a handedness is roughly a few percent, not 100%. This requires water: asteroids or comets brought water (an apparent necessity for life) to early Earth.
But How Do We Get from a Few Percent to 100%? This can apparently occur naturally. Several experiments have been done that suggest that molecules of a tiny fraction of handedness can catalyze synthesis of more of that type, ultimately approaching 100%. This is called “autocatalysis.” So it looks like the few percent could have produced close to the 100% we now find in nature, at least for some amino acids. Then biological processes drive them to 100%.
Do We Understand How Handedness Occurs in Space? Yes, but No. Actually there are several models: Circularly Polarized Light model Molecules are processed by UV light from special cosmic entities, e.g., magnetars. Supernova Neutrino Amino Acid Processing (SNAAP) model Molecules are processed by particles emitted from supernovae in a strong magnetic field. And others, most of which are somewhat convoluted, and probably don’t work.
Since the only data we have, probably for a long time, are from the Solar System, this might provide a plausible explanation. But questions remain unanswered. Circularly Polarized Light Model The CPL Model destroys most of the molecules it processes! That’s a problem!
Supernovae synthesize C, N, O, etc. Racemic mixture of amino acids forms in grains and meteoroids in Supernova nebulae (same number of and ) Neutrinos from other (massive) Supernovae convert racemic to enantiomeric molecules via selec- tive destruction of one chirality of 14 N-based molecules “Rapid” chemical evolution amplifies the enantiomerism as the material in the molecular clouds “slowly” expands to fill the galaxy (more than ) Subsequent generations of stars form, along with planets and biological forms, and evolve to homochiral mole- cules via more amplification when they arrive on planets SNAAP MODEL With amplification, either model may work. So our origins may lie in outer space!
Space Probe ROSETTA ROSETTA will test these models; only LH amino acids would support the SNAAP model. A mixture of LH and RH amino acids would support the circularly polarized light model, but only LH can’t rule it out. Another possible test: ROSETTA (ESA) will sample amino acid handedness on comet 67P/Churyumov- Gerasimenko in 2014.
So How to Get from Molecules of Life to Critters? Most scientists would agree that Darwin was essentially correct. So Nature prepares a bunch of possible creatures, and then lets them decide who the winners are. Extremophiles exist on Earth: see Yellowstone (Octupus Springs)! It appears that whatever conditions the environment presents, Nature will cook up something that can live there (within the limits of the freezing and boiling points of water). But the details are a little murky! And not just on Earth, but presumably on EVERY planet with such conditions!
Four Horsemen of the Apocalypse, Victor Vasnetsov, Pestilence, War, Famine, and Earthquakes What about Large Meteorites? OK, So How Will Life on Earth End? Near Term
But, a Guaranteed End … In 4.5 billion years, the Sun will have converted all its core hydrogen to helium, and its core will contract. Then it will begin “burning” its core helium. This produces more energy, and more pressure. In response, the outside of the star will move outward and the Sun will become a “Red Giant”. When the Sun will becomes a “Red Giant”, it will encompass the Earth. So Earth will be inside of the Sun!
What Will Earthlings Do In 4 Billion Years? Can we keep from destroying ourselves for that long?? Will we choose to just die with Earth? – Probably not! Will we seek another planet in our Solar System? – Nothing works very well! Might we seek another planet in another Stellar System? – There are lots of candidates within a few light years! But other stars have gone into their Red Giant phase; what did the occupants of their planets do? Might some of them have chosen Earth on which to settle? Might space ships be on their way as we speak?
Might some aliens already have landed?! How would we know?
What Would Aliens Look Like? Top of the food chain presumably had to deal with underlings that would evolve to look a lot like Earthly underlings – Alien mammals need to deal with alien lions and tigers – Alien birds with alien condors and buzzards – Alien aquatic creatures with alien sharks Things that work for us, binocular vision, two arms, two legs, “large” brains, opposing thumbs, etc. would presumably also be required of the top of the alien mammalian food chain. And being about the size we are allows us, and them, to be strong enough to overcome our competition, but not so large as to outrun our food supply.
So mammalian aliens might look quite a bit like us.