History & Origin of Earth Life

1. History & Origin of Earth Life ASTR 1420 Lecture 6 Sections 4.2, 4.3, 6.1, 6.2

2. Geology and Life What does geology have to do with Astrobiology? • Because geology provides fossils that are only recorded history of early Earth. Three important aspects of Geology • Volcanism • Plate tectonics (more on following lectures…) • Magnetic field (more on following lectures…)

3. The most precise and quantitative age dating of geological records by radiometric dating (pp 106-110)! Oldest Records Oldest rock Bedrock along the northeast coast of Hudson Bay, Canada, has the oldest rock on Earth. 4.28 billions old

4. Zircon : Commonly used as abrasive and insulate material  formed in an environment with bountiful water Oldest thing on the Earth! Oldest fossil : zircon crystal  common mineral in almost all rocks on the Earth surface. 4.404 billion years old Chemical analysis of this grain suggests that the Earth was cool enough to have water, a hydrospehere and, possibly, life much earlier than previously thought.

5. Age of the Earth • How do we know the age of the Earth? • Oldest rock : 4.0 billions years • Oldest mineral : 4.4 billion years • Apollo Moon rocks : 4.4 billion years • Meteorites : 4.57 billions years • Earth and Moon had formed about 0.05-0.07 billion years after the first meteorites.. • Age of the Earth ~ 4.5 billion years old!

6. Four Eons Hadean  “Hades”, hellish Archean “ancient” Proterozoic “early life” Phanerozoic “visible life” Geological Timescale K-T boundary • End of dinosaurs : 65 Myr • Oxygen build-up : 2.35 Gyr • Oldest microfossil : 3.5 Gyr • Evidence of first life : 3.85 Gyr • Oldest mineral : 4.4 Gyr • Moon impact : ~4.47 Gyr Oldest mineral Evidence of life Oldest microfossil Evidence of oxygen… Moon forming impact

7. Mount St. Helens (May, 1980) Hadeon Earth • Soon after the formation, Earth had neither an atmosphere nor an ocean! ?? For the given b/w Earth & Sun, planete building materials are made of rocks and minerals (no water & gas). Where did water come from? • How were atmosphere and ocean formed? • Outgassing • From impacts • From the oldest rock/mineral and outgassing, about ~100 million years after the formation, Earth is thought to be having continents, oceans, and atmosphere. ? Could there be life in the Hadeon Earth?

8. Early Atmosphere • Mostly CO2, N2, H2O, H2, H2S, SO2… • Then, Cyanobacteria’s photosynthesis  78% N2, 21% O2, 0.1% CO2, etc… • Early life should have been Oxygen-free, if there were any! Current Earth atmosphere is a result of continuous volcanic outgassing + biological modification!

9. When did life begin on Earth?

10. Must rely on fossil records Three possible fossil records Stromatolites Microfossils Carbon isotopes When did life begin? Stromatolites: rocks with a distinctive layered structure. top layer : photosynthesizing microbes + lower layers : microbes depend on the top layer microbes  Waste-deposit creates many layers

11. Stromatolites • As old as 3.5 billion years! • Photosynthetic life already existed about 3.5 billion years ago!  primitive life must have started much earlier!

12. When did life begin? • Oldest Microfossil : Must rely on fossil records • Three possible fossil records • Stromatolites • Microfossils • Carbon isotopes Microfossil of an ancient living cell 3.5 Gyr ago? Still controversial  • Inorganic process (e.g., mineral deposit) can mimic the structure. • Rocks not as old as 3.5 Gyr! • More convincing microfossils exist with more reliable ages (3.2-3.5Gyr, 2.7-3.0Gyr)

13. When did life begin? • Normal Carbon has atomic mass of 12 12C • But, about 11% of C in the nature is 13C • Life can utilize 12C more easily  so, fossils of ancient life show a lower 13C/12C ratio! • Organic carbon ratio was found in 3.85 Gyrold rocks form the coast of Greenland. • other 3.8 Gyr old rock with a similar ratio was found • other isotopes (Fe, N, S) showed the similar results. Must rely on fossil records • Three possible fossil records • Stromatolites • Microfossils • Carbon isotopes

14. Early Origin of Life There are convincing data supporting early life on Earth that had arisen at least 3.5 Gyr ago (or as old as 3.85 Gyr)! • Considering the fact that ancient records as old as 3.5 Gyr are quite rare…  evidence of life in such rare ancient rocks strongly implies the widespread life in young Earth!  could expect life to arise rapidly in a similar fashion on other worlds.  good possibility of common life in the Universe!

15. How did life begin? • Spontaneous Generation (life from non-life…) • Aristotle : • fireflies from a drop of morning dew • frogs from primordial ooze • A Belgian Physician : Prescription for making mice: • old linen + wheat + 21 days  fully-formed mice jumps out!! • Panspermia • Chemical Evolution

16. Panspermia (20th century) Svante Arrhenius (Swedish Physicist, 1903 Nobel Prize in Chemistry) life might have been carried from planet to planet by the transport of metroritic spores • Crick and Orgel (1973) = molybdenum is used by all Earth life even though it is extremely rare! directed panspermia: "seeds" of life exist already all over the Universe that life on Earth may have originated through one of these "seeds”

17. Directed Panspermia(20th century) Crick and Orgel (1973) = molybdenum is used by all Earth life even though it is extremely rare! Many enzymes, for example, require this metal to act. Directed panspermia: "seeds" of life exist already all over the Universe and that life on Earth might have originated through one of these "seeds”

18. Directed Panspermia by Human • Humans are carelessly spreading alien species all over the Earth (loss of native species in CA, Hawaii…) – e.g., coqui frog, poisonous snakes, etc. • If there are numerous long-lived civilizations in the Galaxy, then … • we may be their garbage?

19. Virtue of Panspermia • Conditions may have been more favorable elsewhere – e.g., young Earth may have lacked a Hydrogen-rich atmosphere as used by Julia Child to make primordial soup! • Life elsewhere may be based on a simpler unit than the cell, but only cells made the long journey to Earth • The “elsewhere” might be Mars • Mars to Earth is easier • than Earth to Mars… Why? extra credit

20. Primordial soup : Chemistry  Life

21. Miller-Urey Experiment Experiment to create amino acids (1953) methane water hydrogen ammonia the first experiment to test the theory about the evolution of prebiotic chemicals and the origin of life on Earth.

22. Chemical Evolution Origin of organic material?? • Miller experiment (primordial soup) • Problem : • NH3 and CH4 mixture is not the early Earth atmo.! • It only works well in a reduced atmosphere. • Not enough H2 in the early Earth atmosphere • Cometary delivery of organic molecules to Earth • Organic molecules in space (comet, asteroid, forming stars, etc.) • But, then problem with temperature increase from large impacts (crater size > 260 km) thermophiles first? • Chemical reactions near the deep sea vent : energy and materials…

23. Chemistry  Biology Randomly putting molecules together in primordial soup does not work  can put amino acids and nucleotides together in jillion different ways in polypeptides and polynucleotides. • Assuming an optimum rate of chemical reaction in primordial soup, randomly putting together and breaking apart molecules even in 1 billion years couldn’t make even a virus (50 genes) much less than E coli bacteria  human 30,000 genes • Need a molecule that is simpler than DNA but still capable of replication  RNA? • DNA nor RNA cannot replicate itself alone! • RNA cannot replicate without enzymes and enzymes cannot be made without RNA : “chicken and egg”  Thomas Cech (1980s) found RNA molecules can catalyze their own replication (Nobel Prize in 1989) • “RNA world” : RNA molecules serve both as genes and enzymes.

24. How RNA world started? • Spontaneous production of RNA is impossible! Too complex still… • Clay : very common  weathered silicate minerals (i.e., nearly all rocks) have layers to which other molecules (organic molecules) adhere! • On the surface of clay, organic materials force to stay in proximity increasing a chance of forming more complex structure. • Lab experiments produced ~100 bases RNA strands! • periodic evaporation and minor freezing might have separated organic polymers from H2O increasing the chance! • Natural selection at the molecular level : The RNA molecules that replicated faster and more accurately soon to dominate!

25. Pre-cells • Molecular evolution would have been much more efficient if RNA and other molecules are confined in a structure. • Increasing the rate of reaction • Isolating its content to facilitate natural selection among RNA molecules! If no such enclosure, enzyme created by the best RNA can help other RNAs. Left: microscopic spheres made by cooling a warm solution of amino acids Right : microscopic membranes made from lipids mixed with water (instantaneously formed!)

26. Lipid pre-cell can form on the surface of clay! + Very high chance of making RNA on the surface of clay with membrane!! Right: lab experiment shows RNA strands (red) entrapped within a lipid pre-cell (green circle) made on the surface of clay! RNA cell?

27. Chemistry on the early Earth

28. In summary… Important Concepts Important Terms Panspermia Primordial soup Outgassing RNA world • Miller-Urey experiment • Early start of Earth life and its implication to life elsewhere • Chemical evolution to DNA • Evolution of Earth Atmosphere • Earliest life would’ve been extremophiles • Importance of Clay • Pre-cell structure and its importance • Chapter/sections covered in this lecture : 4.2, 4.3, 6.1, & 6.2 • Habitability of Earth : next class