The Early Earth and The Origin of Life

Biology LecturePost Falls HS

Info from Dr. Karen KolehmainenDepartment of Physics, CSUSB

HOW IS THE ABSOLUTE AGE OF A ROCK OR FOSSIL DETERMINED?

RADIOACTIVE DATING

TO UNDERSTAND HOW, WE MUST FIRST UNDERSTAND THE NATURE OF RADIOACTIVITY.

TYPES OF RADIOACTIVITY ALPHA DECAY

– A 4He NUCLEUS (2 PROTONS + 2 NEUTRONS) IS EJECTED FROM A LARGE NUCLEUS.

BETA DECAY– A NEUTRON CHANGES INTO A PROTON, CAUSING AN

ELECTRON TO BE EJECTED FROM THE NUCLEUS, OR…– A PROTON CHANGES INTO A NEUTRON, ACCOMPANIED BY

EITHER THE CAPTURE OF A ELECTRON BY THE NUCLEUS OR THE EJECTION OF A POSITRON (ANTIPARTICLE OF THE ELECTRON).

GAMMA DECAY– PROTONS AND NEUTRONS REARRANGE THEMSELVES INSIDE

THE NUCLEUS, EMITTING A HIGH ENERGY PHOTON (GAMMA RAY).

NOTE: IN BOTH ALPHA AND BETA (BUT NOT GAMMA) DECAY, THE DAUGHTER NUCLEUS IS A DIFFERENT ELEMENT THAN THE PARENT NUCLEUS.

HALF-LIFE

THE HALF-LIFE IS DEFINED AS THE INTERVAL OF TIME DURING WHICH A NUCLEUS HAS A 50% CHANCE OF DECAYING.

AFTER ONE HALF-LIFE HAS ELAPSED, APPROXIMATELY HALF OF THE NUCLEI IN A SAMPLE WILL HAVE DECAYED.

EACH RADIOACTIVE ISOTOPE HAS A DIFFERENT HALF-LIFE, WITH VALUES RANGE FROM A FRACTION OF A SECOND TO BILLIONS OF YEARS.

HALF-LIFE EXAMPLE: CONSIDER A MATERIAL WITH A HALF-

LIFE OF 1 YEAR. INITIALLY, 1000 NUCLEI ARE PRESENT IN A PARTICULAR SAMPLE.

AFTER 1 YEAR HAS ELAPSED, APPROXIMATELY 500 (OR 1/2) HAVE DECAYED, AND 500 (1/2) HAVE NOT YET DECAYED. PARENT AND DAUGHTER ARE EQUALLY ABUNDANT.

AFTER 2 YEARS, APPROXIMATELY 750 (3/4) HAVE DECAYED, AND 250 (I/4) HAVE NOT YET DECAYED. DAUGHTER IS 3 TIMES AS ABUNDANT AS PARENT.

AFTER 3 YEARS, APPROXIMATELY 875 (7/8) HAVE DECAYED, AND 125 (1/8) HAVE NOT YET DECAYED. DAUGHTER IS 7 TIMES AS ABUNDANT AS PARENT.

DECAYS CONTINUE IN THIS MANNER.

RADIOACTIVE DATING COMPARE ABUNDANCES OF THE PARENT

AND DAUGHTER ISOTOPES TO DETERMINE HOW MUCH TIME HAS ELAPSED (SINCE WHEN?).

DATING OF A ROCK MEASURES THE TIME SINCE THE ROCK SOLIDIFIED.

FOR AN IGNEOUS ROCK, THIS GIVES THE AGE OF THE ROCK.

RADIOACTIVE DATING THE TECHNIQUE ISN’T DIRECTLY USEFUL FOR A

SEDIMENTARY ROCK (THE ONLY TYPE IN WHICH FOSSILS ARE FOUND). IT WILL ONLY GIVE THE AGE SINCE THE SMALL GRAINS INSIDE THE ROCK SOLIDIFIED, NOT THE TIME SINCE THE SEDIMENTS WERE DEPOSITED OR COMPRESSED TO FORM THE SEDIMENTARY ROCK.

HOWEVER, IF A SEDIMENTARY ROCK LAYER IS “SANDWICHED” BETWEEN TWO IGNEOUS ROCK LAYERS, THE TECHNIQUE WILL PUT CONSTRAINTS ON THE AGE IN THE IN-BETWEEN LAYER.

FOR EXAMPLE, CONSIDER A SEDIMENTARY ROCK LAYER SANDWICHED BETWEEN TWO LAYERS OF IGNEOUS ROCK. THE LAYER OF IGNEOUS ROCK ON TOP IS 100 MILLION YEARS OLD, AND THE LAYER OF IGNEOUS ROCK UNDERNEATH IS 110 MILLION YEARS OLD. THEN THE SEDIMENTARY ROCK (AND ANY FOSSILS IN IT) IS SOMEWHERE BETWEEN 100 AND 110 MILLION YEARS OLD.

EXAMPLESPARENT

URANIUM 238

POTASSIUM 40

URANIUM 235

CARBON 14

DAUGHTER

LEAD 206

ARGON 40

LEAD 207

NITROGEN 14

HALF-LIFE(YEARS)

4.47 BILLION

1.25 BILLION

704 MILLION

5730

TYPE

CHAIN*

BETA

CHAIN*

BETA

*CHAIN MEANS A SEQUENCE OF SEVERAL DECAYS (POSSIBLY OF DIFFERENT TYPES), NOT JUST A SINGLE DECAY

COMPLICATION IF SOME OF THE DAUGHTER ISOTOPE WAS

PRESENT INITIALLY, IT WILL ALTER THE RELATIVE ABUNDANCES AND GIVE AN INCORRECT AGE (UNLESS WE COMPENSATE FOR THIS).

EASIEST SOLUTION: USE A DECAY PROCESS FOR WHICH THE DAUGHTER ISOTOPE IS GASEOUS AND WOULD HAVE ESCAPED FROM THE ROCK WHILE IT WAS STILL MOLTEN. THEN ANY DAUGHTER NUCLEI PRESENT MUST HAVE RESULTED FROM DECAY OF THE PARENT AFTER THE ROCK SOLIDIFIED. (THEN THE GAS WOULD BE TRAPPED INSIDE THE ROCK.)

FOR CASES WHERE THE DAUGHTER ISN’T GASEOUS, GEOLOGISTS HAVE OTHER WAYS OF ESTIMATING THE ABUNDANCE OF THE DAUGHTER ISOTOPE PRESENT INITIALLY.

REASONS TO BE CONFIDENT ABOUT RESULTS

AGES DETERMINED VIA DIFFERENT RADIOACTIVE ISOTOPES AGREE.

AGES OF FOSSILS OF A GIVEN SPECIES AGREE, EVEN IF FOUND IN DIFFERENT LOCATIONS.

AGES ARE CONSISTENT WITH RELATIVE AGES DETERMINED BY ORDERING OF LAYERS IN ROCK.

AGES AGREE WITH THOSE FOUND VIA OTHER MEANS (SUCH AS RELAXATION OF L AMINO ACIDS TO A 50-50 MIX OF L AND D AMINO ACIDS IN DEAD ORGANISMS).

FORMATION OF THE EARTH FORMED (ALONG WITH THE SUN AND THE REST OF

THE SOLAR SYSTEM) OUT OF A NEBULA 4.6 BILLION YEARS AGO

VERY HOT INITIALLY DUE TO HEAT OF FORMATION AND HEAT RELEASED BY INTERNAL RADIOACTIVE DECAY

MOLTEN AT FIRST, THEN COOLED & SOLIDIFIED & DIFFERENTIATED (SEPARATED INTO LAYERS)

NO ATMOSPHERE INITIALLY – GRAVITY NOT STRONG ENOUGH TO HOLD ONTO LIGHT ELEMENTS

ATMOSPHERE AND WATER ADDED LATER VIA OUTGASSING AND COMETARY IMPACTS

ATMOSPHERE AND OCEANS ATMOSPHERE AND OCEANS FORMED VIA:

– BOMBARDMENT BY COMETS AND ASTEROIDS – OUTGASSING (RELEASE OF GAS PREVIOUSLY

TRAPPED INSIDE ROCK) FROM VOLCANOES

EARLY ATMOSPHERE WAS VERY DIFFERENT FROM CURRENT ATMOSPHERE– CONSISTED MOSTLY OF CARBON DIOXIDE (CO2),

CARBON MONOXIDE (CO), NITROGEN (N2), AND WATER VAPOR (H20)

– NO OXYGEN – CURRENT ATMOPSHERE IS MOSTLY NITROGEN

(N2) AND OXYGEN (O2)

DEVELOPMENT OF ATMOSPHERE ULTRAVIOLET (UV) RADIATION FROM THE SUN BROKE

APART MANY MOLECULES INTO INDIVIDUAL ATOMS. HYDROGEN (H AND H2) ESCAPED TO SPACE. (EARTH’S

GRAVITY ISN’T STRONG ENOUGH TO HOLD ONTO SUCH LIGHT FAST-MOVING OBJECTS.)

SMALL AMOUNTS OF OXYGEN (O2) AND OZONE (O3) MOLECULES FORMED, THE LATTER PROTECTING THE SURFACE FROM UV RADIATION.

MOST CO2 WAS PULLED OUT OF ATMOSPHERE AND INCORPORATED INTO CARBONATE ROCKS (ACCELERATED BY LIFE, ONCE IT GETS STARTED).

CYANOBACTERIA (EARLY FORM OF LIFE) RELEASED OXYGEN INTO THE ATMOSPHERE.

THE ATMOSPHERE WAS CHANGED DRASTICALLY BY THE PRESENCE OF LIFE!

TODAY’S ATMOSPHERE

78 % NITROGEN (N2) 21 % OXYGEN (O2) 1% ARGON (Ar) 0.01 % CARBON DIOXIDE (CO2)

PLANTS TAKE IN CO2 AND RELEASE O2

ANIMALS TAKE IN O2 AND RELEASE CO2

THE EFFECTS OF ANIMALS VS. PLANTS COMPENSATE FOR EACH OTHER TO KEEP THE AMOUNTS OF O2 AND CO2 ROUGHLY CONSTANT.

LIFE AND THE ATMOSPHERE

LIFE ON EARTH ORIGINATED IN AN ATMOSPHERE CONTAINING VERY LITTLE OXYGEN.

LIVING THINGS THEN CHANGED THE ATMOSPHERE, ADDING LARGE AMOUNTS OF OXYGEN.

IN AN ATMOSPHERE CONTAINING OXYGEN, COMPLEX ORGANIC MOLECULES CANNOT FORM. OXYGEN INTERACTS WITH THEM AND BREAKS THEM APART.

THEREFORE, IF LIFE ON EARTH WERE DESTROYED NOW, IT PROBABLY COULDN’T GET STARTED AGAIN.

GREENHOUSE EFFECTSUNLIGHT (MOSTLY VISIBLE LIGHT) IS ABSORBED BY A PLANET’S SURFACE. ENERGY IS RE-RADIATED FROM THE GROUND (WHICH ACTS AS A BLACKBODY), MOSTLY AS INFRARED RADIATION. INFRARED RADIATION IS ABSORBED BY ATMOSPHERIC GREENHOUSE GASES: CO2 ,H2O, CH4, AND OTHERS.ATMOSPHERE WARMS, AND THEREFORE RADIATES (AS A BLACKBODY) MORE RADIATION TO SPACE.EVENTUALLY EQUILIBRIUM IS REACHED SO THAT ENERGY ABSORBED = ENERGY RADIATED, AND TEMPERATURE STABILIZES.FINAL TEMPERATURE IS HOTTER THAN IT WOULD BE WITHOUT ABSORPTION OF INFRARED RADIATION BY ATMOSPHERIC GREENHOUSE GASES.

GREENHOUSE EFFECT

BECAUSE OF THE GREENHOUSE EFFECT, EARTH IS 40K (OR 40OC) HOTTER THAN IT OTHERWISE WOULD BE.

HUMAN INDUSTRIAL ACTIVITY IS ADDING MORE GREENHOUSE GASES TO EARTH’S ATMOSPHERE.

“GLOBAL WARMING” (AN INCREASE IN AVERAGE PLANET-WIDE TEMPERATURES OVER THE LAST CENTURY OR SO) HAS BEEN MEASURED AND IS REALLY HAPPENING. THE SCIENTIFIC EVIDENCE IS OVERWHELMING THAT HUMAN ACTIVITY IS RESPONSIBLE.

CLAIMS TO THE CONTRARY ARE PROBABLY “WISHFUL THINKING” OR POLITICALLY MOTIVATED.

WHEN DID LIFE BEGIN? PROBABLY BETWEEN 3.9 AND 4.2 BILLION

YEARS AGO THIS WAS 0.4 TO 0.7 BILLION YEARS (OR 400 TO

700 MILLION YEARS) AFTER THE EARTH FORMED.

COMPARED TO THE CURRENT AGE OF THE EARTH (4.6 BILLION YEARS), THIS ISN’T MUCH TIME.

LIFE GOT STARTED VERY QUICKLY AFTER THE EARTH FORMED BUT WAS VERY PRIMITIVE!

EVIDENCE FOR EARLY LIFE:– ANCIENT MICROFOSSILS– STROMATOLITES– ISOTOPIC ABUNDANCES OF CARBON

WHEN DID LIFE BEGIN?

MOST OF THE EARTH’S HISTORY HAS BEEN SPENT WITH LITTLE OR NO LIFE PRESENT – 88%

FORMERLY KNOWN AS THE PRECAMBRIAN ERA

NOW IT HAS BEEN BROKEN UP INTO SIGNIFICANT SECTIONS

WHERE DID LIFE BEGIN? PROBABLY NOT ON DRY LAND

– IMPACTS AND/OR OTHER ENVIRONMWENTAL HAZARDS WOULD MOST LIKELY WIPE IT OUT.

– HARD FOR MOLECULES TO REACT ENOUGH TO PRODUCE LONG POLYMERS UNLESS DISSOLVED IN A LIQUID.

POSSIBILITIES:– OCEANS– SMALL POOLS OF WATER (TIDEPOOLS?)– HOT SPRINGS– NEAR HYDROTHERMAL VENTS (ON OCEAN FLOORS)– INSIDE ROCKS

OR MAYBE LIFE WAS DELIVERED TO EARTH FROM AN EXTRATERRESTRIAL SOURCE, AS OPPOSED TO HAVING ORIGINATED HERE.

THE “SEEDING” OF LIFE ON EARTH FROM AN EXTRATERRESTRIAL SOURCE (ARRHENIUS, 1907)

HOW IT WORKS:• SMALL ORGANISMS ARE BLOWN INTO THE UPPER

ATMOSPHERE OF A DISTANT “SOURCE” PLANET.• ORGANISMS MUST BE THE SIZE OF BACTERIA,

SPORES, OR VIRUSES.• SMALL ORGANISMS WOULD BE BLOWN OUT OF THE

ATMOSPHERE AND INTO INTERSTELLAR SPACE BY THE PRESSURE OF SUNLIGHT.

• ALTERNATIVELY, AN IMPACT COULD HAVE THROWN ORGANISMS (MAYBE INSIDE ROCKS) INTO SPACE.

BUT HOW DID LIFE START ON THE “SOURCE” PLANET? THE QUESTION OF THE ULTIMATE SOURCE OF LIFE IS NOT ANSWERED!

PANSPERMIA

IN THE 1960’s, CARL SAGAN AND OTHERS SHOWED:• ORGANISMS WOULD LIKELY BE ERODED AWAY BY

COLLISIONS WITH INTERSTELLAR GAS AND DUST.

• ORGANISMS WOULD LIKELY BE KILLED BY EITHER ULTRAVIOLET LIGHT FROM STARS OR COSMIC RAYS.

• STATISTICALLY, A LARGE NUMBER OF “SOURCE” PLANETS ARE REQUIRED TO PROVIDE EARTH WITH EVEN ONE MICROORGANISM.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

THE “NEW” PANSPERMIA

SIMPLE ORGANIC MOLECULES (BUT NOT ACTUAL ORGANISMS) WERE DELIVERED TO EARTH VIA IMPACTS OF COMETS AND ASTEROIDS.

DID LIFE BEGIN IN WATER POOLS? WATER DISSOLVES MOLECULES SO THAT THEY

CAN MOVE AROUND AND INTERACT MORE EASILY TO FORM LARGE MOLECULES.

WATER POOL PROVIDES SOME PROTECTION FROM ENVIRONMENTAL HAZARDS (BUT NOT AS MUCH AS VENT ENVIRONMENT DOES).

SMALL BODY OF WATER ALLOWS CHEMICALS TO BECOME MORE CONCENTRATED THAN IN A LARGE BODY OF WATER LIKE AN OCEAN.

IN A TIDEPOOL, TIDES OCCASIONALLY BRING IN NEW MATERIALS.

SOLID SUBSTRATE (CLAY) COULD AID IN LINING UP MONOMERS TO FORM POLYMERS, AND IN SELECTING ONE HANDEDNESS OF MOLECULES.

HOW DID LIFE BEGIN? SIMPLE ORGANIC MOLECULES WERE DELIVERED

TO EARTH VIA COMET AND ASTEROID IMPACTS, AND/OR PRODUCED ON THE EARTH (IN TIDEPOOLS OR NEAR HYDROTHERMAL VENTS?) VIA CHEMICAL REACTIONS.

SIMPLE ORGANIC MOLECULES COMBINE TO MAKE LONG POLYMERS, SOME OF WHICH MUST BE SELF-REPLICATING (LIKE DNA OR RNA).

POLYMERS ARE ENCLOSED INSIDE A “CELL” THAT IS SEPARATED FROM ITS ENVIRONMENT BY A MEMBRANE.

MILLER-UREY EXPERIMENTS

ATTEMPTS TO CREATE LIFE IN THE LABORATORY

PROVIDE A MIXTURE OF GASES SIMILAR TO THAT IN THE EARLY ATMOSPHERE

PROVIDE WATER TO SIMULATE OCEANS OR POOLS

PROVIDE A SOURCE OF ENERGY

WAIT AND SEE WHAT HAPPENS

WATER

GASES:• H2O (WATER VAPOR)

• CO2 (CARBON DIOXIDE)

• N2 (NITROGEN)

• H2 (HYDROGEN)

• CH4 (METHANE)

• NH3 (AMMONIA)

ENERGY:• HEAT• ELECTRIC SPARK (LIGHTNING)• ULTRAVIOLET LIGHT

TIME (WAIT A FEW DAYS TO WEEKS)

INGREDIENTS FOR MILLER-UREY EXPERIMENTS

RESULTS

MANY ORGANIC MOLECULES ARE PRODUCED, INCLUDING:

SUGARS (INCLUDING RIBOSE) FATS OR LIPIDS AMINO ACIDS (50% L AND 50% D) GENETIC BASES

NOTE: IF OXYGEN IS PRESENT, THESE MOLECULES ARE NOT FORMED!!

(IF OXYGEN IS PRESENT, EVERYTHING CO2 & H2O)

LIMITATIONS

NOT ALL IMPORTANT ORGANIC MOLECULES ARE FORMED.

NO LIVING ORGANISMS ARE FORMED.

WHY? MAYBE BASIC IDEA IS WRONG. MAYBE MORE TIME IS NEEDED (MILLIONS

OF YEARS, NOT JUST A FEW WEEKS OR MONTHS).

MAYBE SOME KEY INGREDIENT IS MISSING.

SOURCES OF SIMPLE ORGANIC MOLECULES ON EARLY EARTH MILLER-UREY TYPE REACTIONS IN

– THE ATMOSPHERE– SMALL POOLS OF WATER– OCEANS NEAR HYDROTHERMAL VENTS

DELIVERY VIA COMET AND ASTEROID IMPACTS

THESE PROBABLY ALL PLAYED A ROLE. BUT THIS ISN’T LIFE YET! WHAT HAPPENED NEXT?