Origins of Life Stephen Eikenberry 18 January 2013

Origins of Life Stephen Eikenberry 18 January 2013 AST 2037 1

POP QUIZ!! 1. The Earth's atmosphere is mostly made of what element? 2. What element is the most versatile in its bonding (and critical for life)? 2

How Did Life Come About? • First things first: I don’t know! • Second: Anyone who says they have a proven scientific explanation (currently) is probably selling something! • That said … there ARE some things we know, and some we strongly suspect • From them, we can at least TRY to put together a rough sketch of how life probably arose here on Earth • Let’s do that! 3

What do we have to work with? • In the beginning … • OK, well, not really the beginning. More like: • About 8 billion years after the Big Bang • About 500 million years after the Solar System began to form • About 4. 6 billion years before TODAY • What was Earth like? • Young, recently-solidified surface • Accretion of material from planetesimals nearing an end (end of the “Early Heavy Bombardment”) • How do we know? 4

Earth: T – 4. 6 Billion Yrs • • • Rocks were just solidifying on surface How do we know? Age-dating of the oldest known rocks From what? Radioactive isotope dating Huh? First: what’s an isotope? 5

Elements and Isotopes • An “element” has a certain number of protons and electrons • For instance, hydrogen (H) has 1 of each • Oxygen (O) has 8 of each • Carbon (C) has 6 of each • “Isotopes” of a given element have the same number of protons/electrons, but different numbers of neutrons in the nucleus: • “Normal” H has 0 neutrons, deuterium has 1 neutron, tritium has 2 neutrons – but ALL are still hydrogen • O 16 is “normal” oxygen, most common – has 8 protons and 8 neutrons (8+8 = 16) • O 18 is more rare (8 protons + 10 neutrons = 18) • C 12 (6+6) is common, C 14 (6+8) is rare – and radioactive!! 6

Radioactive Decay • Many non- “normal” isotopes are radioactive, and they “decay” into other elements • This process converts a “parent” to a “daughter” isotope • This happens on a known timescale called the “halflife” of the decay (the time it takes for ½ of the parent atoms to decay) 7

Radioactive Age-Dating • So … by counting parent/daughter atoms inside a rock, we KNOW how many half-lives since the rock solidified from magma • We can measure the atomic half-life in a physics lab (or, even calculate it from quantum physics these days) • Then, we know HOW OLD the rock is … 8

Some Handy Decays Parent Isotope Stable Daughter Product Half-Life Uranium-238 Lead-206 4. 5 billion yr Uranium-235 Lead-207 704 million yr Thorium-232 Lead-208 14. 0 billion yr Rubidium-87 Strontium-87 48. 8 billion yr Potassium-40 Argon-40 1. 25 billion yr Samarium-147 Nedodymium-143 106 billion yr 9

Earth: T – 4. 4 Billion Yrs • Atmosphere & oceans – non-existent!! • How do we know? Rocks formed back then had very little “volatiles” in them (i. e. H, H 2 O, O 2, etc. ) • What happened to volatiles? Solar wind (show) 10

How Did We Get Oceans? • From Outer Space! Comet/Ocean Theory: • Comets (big balls of ice) crash into baby Earth • Crash melts/vaporizes the ice • Once the steam cools, it condenses • The liquid water flows “downhill” and pools together • This makes oceans • Also brings lots of other “volatile” materials 11

Cometary Bombardment • We KNOW comets hit planets – Jupiter & Comet Shoemaker-Levy 9 • Consistent with Early Heavy Bombardment (how do we know? Moon craters) • Deuterium problem: Most current comets we see have water with too little deuterium compared to water in Earth’s oceans 12

Deuterium Issue Resolved! • We know from meteors & space probes that the inner Solar System has more heavy isotopes than the outer Solar System • We think this is due to the solar wind • Almost all known comets today are in the outer SS • But, back in the day, inner SS would have had comets too (those are the most likely to hit Earth in the Early Heavy BB!) • Suggestion: Maybe inner SS comet water would have deuterium abundance like Earth’s ocean water (? ) • In 2005, Gemini Observatory measured deuterium abundance from H 20 in asteroid belt comets matches Earth water !!! 13

What was our Young Atmosphere Like? • Unbreathable! • Mostly carbon monoxide (CO), carbon dioxide (CO 2), nitrogen (N 2) and water vapor (H 2 O) • How do we know? Rock chemistry from that time period shows these compounds • But … no O 2 • Note: free oxygen is very “aggressive” in forming chemical bonds and does bad things to many chemicals (i. e. iron rusts!) • So … even a little O 2 would be pretty obvious in these rocks it just wasn’t there! 14

Summary So Far 15

Then … Life Appears! • First fossil cells found in rocks at about T – 3. 7 to T – 3. 5 Billion Years! • Tiny little things • Not O 2 breathers like us (none around!) • Probably CO 2 breathers • Modern cyanobacteria look a lot like these fossils AND they are CO 2 breathers • Suggests that the first (fossil) life may have been cyanobacteria (? ) 16

HOW Did Life Appear? • It must have formed SOMEHOW! • What do we need? • Atmosphere – got one! • DNA or something like it – not obviously there (!) • COULD DNA form back then? • Need amino acids, sugars, phosphates DNA building blocks • Could THEY form? 17

Urey-Miller Experiment • Basic idea: • Take a bunch of chemicals as known to present in the early atmosphere & ocean • Put them in a chemistry lab setup with circulating gases • Simulates “Primordial Soup” • Zap the whole thing with electric discharge (like lightning!) • See what happens … 18

Urey-Miller: Results • What did they find? • Amino Acids!!! (Lots of them!) • More specifically: • 13 amino acids used in life; (both L- and R- type) • Sugars • Lipids • About 10 -15% of the carbon ended up in protein structures like this • Summary: With the KNOWN chemicals and KNOWN environment in the early Earth, we EXPECT complex amino acids, sugars, and other organic chemicals to form in nature (!!) 19

Meteor Aminos • • The Murchison Meteorite is a big chunk of space rock Chemical analysis shows: Amino Acids! It is another source of aminos! Diversity? 20

List of Murchison Amino Acids Amino Alkanoic Acids 2 Carbon: Glycine 3 Carbon: Alanine b-alanine Serine Sarcosine 4 Carbon: Threonine a-Aminobutyric Acid b-Aminobutyric Acid g-Aminobutyric Acid a-Aminoisobutyric Acid b-Aminoisobutyric Acid N-Ethylglycine N, N-dimethylglycine N-Methylalanine N-methyl-b-alanine 5 Carbon: Valine Isovaline Norvaline Proline Methionine 3 -Amino-2 -ethylpropanoic Acid 3 -Amino-2, 2 -dimethylpropanoic Acid 3 -Amino-2 -methylbutanoic Acid 3 -Amino-3 -methylbutanoic Acid 4 -Amino-2 -methylbutanoic Acid 4 -Amino-3 -methylbutanoic Acid Allo-3 -amino-2 -methylbutanoic Acid 3 -Aminopentanoic Acid 4 -Aminopentanoic Acid 5 -Aminopentanoic Acid Amino Dialkanoic Acids 4 Carbon: Aspartic Acid 5 Carbon: Glutamic Acid 2 -Methylaspartic Acid 3 -Methylaspartic Acid Allo-3 -methylaspartic Acid N-Methylaspartic Acid 6 Carbon: a-Aminoadipic Acid 2 -Methylglutamic Acid 7 Carbon: a-Aminopimelic Acid Amino Alkanoic Acids 6 Carbon: Leucine Isoleucine Alloisoleucine Norleucine Pseudoleucine Cycloleucine 2 -Methyl-norvaline Pipecolic Acid 2 -Amino-2 -ethylbutanoic Acid 3 -Amino-2 -ethylbutanoic Acid* 2 -Amino-2, 3 -dimethylbutanoic Acid 3 -Amino-2, 3 -dimethylbutanoic Acid* 4 -Amino-3, 3 -dimethylbutanoic Acid* 3 -Amino-3 -methylpentanoic Acid* 4 -Amino-2 -methylpentanoic Acid* 4 -Amino-3 -methylpentanoic Acid* 4 -Amino-4 -methylpentaoic Acid* 3 -methylamine-pentanoic Acid* 4 -Aminohexanoic Acid* 7 Carbon: 2 -Amino-2, 3, 3 -trimethylbutanoic Acid 2 -Amino-2 -ethyl-3 -methylbutanoic Acid 2 -Amino-2 -ethylpentanoic Acid 2 -Amino-3 -ethylpentanoic Acid 2 -Amino-2, 3 -dimethylpentanoic Acid 2 -Amino-2, 4 -dimethylpentanoic Acid 2 -Amino-3, 3 -dimethylpentanoic Acid 2 -Amino-3, 4 -dimethylpentanoic Acid 2 -Amino-4, 4 -dimethylpentanoic Acid Allo-2 -amino-2, 3 -dimethylpentanoic Acid* Allo-2 -amino-3, 4 -dimethylpentanoic Acid 2 -Amino-2 -methylhexanoic Acid 2 -Amino-3 -methylhexanoic Acid 2 -Amino-4 -methylhexanoic Acid 2 -Amino-5 -methylhexanoic Acid Allo-2 -amino-3 -methylhexanoic Acid* 21

Meteors: Source for Life? • Note: L/R evenly made here too • Is this the source? • Probably not: • Not that much amino abundance, and the compounds are stuck inside a rock • To get enough on Earth, need lots of bombarding • (but that melts rocks and destroys aminos) 22

Got Aminos, etc. – Now What? • Then, need to put them all together in polymer chains • “Polymerization” of the Primordial Soup • How … ? ? 23

Polymerization • In order to polymerize organic compounds, we would need: • Stable environment • No big temperature variations • No major mechanical shaking • Lots of surface area • Points for the various organic compounds to attach • Perhaps a pattern to it • Provides chemical/physical energy advantage for pattern formation in the polymer too • Where do we find that? 24

Clays • Naturally-occurring silts made from silicates • Clay in water can provide steady temperature and protect anything inside from shaking/waves • Tend to crystalline-like structures (patterns) with HUGE surface area • Known to assist (“catalyze”) organic reactions in labs • Could they be the place 25

Life’s Little Irony • Stereotypical Creationist to Stereotypical Evolutionist: You’re an arrogant fool! • Stereotypical Evolutionist to Stereotypical Creationist: You’re an arrogant fool! • Question to both: How do you make humans? • Creationist: God scooped up some clay, molded it to human shape, and breathed on it. • Evolutionist: Well, see … first you get yourself some nice clay … 26

Direct jump to DNA? • • Maybe … but that is a lot of change of complexity in one hop! RNA is simpler than DNA Some critters (i. e. some viruses) seem to run on RNA-only But … they seem to be dependent on DNA-bearing hosts for survival (? ? ) • At least opens the possibility of “RNA world” life, which then evolved into more complex “DNA-world” we all know and love today 27

Another theory • Panspermia: Life is commonly present out in space, and was carried to Earth as spores trapped in meteors • But … radiation issues make this seem a little less likely 28

Summary • • • Earth of Way Back When was different We can tell from chemical and radio-isotope analysis of rocks Water and other volatiles may have come from comet impacts Life formed a long time ago – about 3. 5 Billion Yr or so We know from fossils We don’t know exactly how, but … • We know we had the right elements • Those elements + lightning make amino acids • DNA may have originated from these acids in a clay matrix • Next question: How did things get from Then to Now? ? 29