history & origin of earth life
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History & Origin of Earth Life. ASTR 1420 Lecture 6 Sections 4.2, 4.3, 6.1, 6.2. 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 - PowerPoint PPT PresentationTRANSCRIPT
History & Origin of Earth Life
ASTR 1420
Lecture 6
Sections 4.2, 4.3, 6.1, 6.2
Geology and Life
What does geology have to do with Astrobiology?
o Because geology provides fossils that are only recorded history of early Earth.
Three important aspects of Geology
1. Volcanism2. Plate tectonics (more on following lectures…)3. Magnetic field (more on following lectures…)
Oldest RecordsOldest rock
Bedrock along the northeast coast of Hudson Bay, Canada, has the oldest rock on Earth.
4.28 billions old
The most precise and quantitative age dating of geological records by radiometric dating (pp 106-110)!
Oldest thing on the Earth!
Oldest fossil : zircon crystal common mineral in almost all rocks on the Earth surface.
• Zircon : Commonly used as abrasive and insulate material formed in an environment with bountiful water
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.
4.404 billion years old
Age of the Earth
• How do we know the age of the Earth?
o Oldest rock : 4.0 billions years o Oldest mineral : 4.4 billion years o Apollo Moon rocks : 4.4 billion yearso 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!
Geological Timescale
Four Eons• Hadean “Hades”, hellish• Archean “ancient”• Proterozoic “early life”• Phanerozoic “visible life”
Moon forming impact
Oldest mineral
Evidence of life
Oldest microfossil
Evidence of oxygen…
K-T boundary
End of dinosaurs : 65 MyrOxygen build-up : 2.35 GyrOldest microfossil : 3.5 GyrEvidence of first life : 3.85 GyrOldest mineral : 4.4 GyrMoon impact : ~4.47 Gyr
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?o Outgassingo 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?
Mount St. Helens (May, 1980)
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 + biologicalmodification!
When did life begin on Earth?
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
Must rely on fossil recordsThree possible fossil
records1. Stromatolites2. Microfossils3. Carbon isotopes
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!
• Oldest Microfossil :
• Inorganic process (e.g., mineral deposit) can mimic the structure.•Rocks not as old as 3.5 Gyr!
Still controversial
Microfossil of an ancient living cell 3.5 Gyr ago?
More convincing microfossils exist with more reliable ages (3.2-3.5Gyr, 2.7-3.0Gyr)
Must rely on fossil recordsThree possible fossil
records1. Stromatolites2. Microfossils3. Carbon isotopes
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 Gyr old 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 recordsThree possible fossil
records1. Stromatolites2. Microfossils3. Carbon isotopes
When did life begin?
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!
How did life begin?• Spontaneous Generation (life from non-life…)o Aristotle :
fireflies from a drop of morning dew frogs from primordial ooze
o A Belgian Physician : Prescription for making mice: old linen + wheat + 21 days fully-formed mice jumps out!!
• Panspermia
• Chemical Evolution
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
o 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”
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”
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?
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 Marso Mars to Earth is easiero than Earth to Mars… Why? extra credit
Primordial soup : Chemistry Life
Miller-Urey ExperimentExperiment to create amino acids
(1953)
methane
hydrogen
water
ammonia
the first experiment to test the theory about the evolution of prebiotic chemicals and the origin of life on Earth.
Chemical Evolution
Origin of organic material??o 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
o 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?
o Chemical reactions near the deep sea vent : energy and materials…
Chemistry BiologyRandomly putting molecules together in primordial soup does not work can put amino acids and nucleotides together in jillion different ways in polypeptides and
polynucleotides.o 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.
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!
Pre-cells
• Molecular evolution would have been much more efficient if RNA and other molecules are confined in a structure.o Increasing the rate of reactiono 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 acidsRight : microscopic membranes made from lipids mixed with water (instantaneously formed!)
RNA cell?
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!
Chemistry on the early Earth
In summary…
Important Concepts• 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
Important Terms• Panspermia• Primordial soup• Outgassing• RNA world
Chapter/sections covered in this lecture : 4.2, 4.3, 6.1, & 6.2Habitability of Earth : next class