Chapter 25 Flashcards
Geologic time is divided into four eons, what are they?
Hadean, Archean, Proterozoic and Phanerozoic
Eons are subdivided into eras, which are further subdivided into periods
please study the image on slide 4 on the ch.25 PowerPoint as it gives all the info on major events in geologic history and in which, eon, era, and period they occurred in
What was Hadean Earth?
a hot mass of molten rock about 4.6 BYA
As it cooled, much of the water vapor present in Earth’s atmosphere condensed into liquid water that accumulated on the surface in chemically rich oceans. One scenario for the origin of life is that it originated in these oceans
Hadean Earth was pummeled by asteroids, which could potentially vaporize entire oceans.
When meteor hit, debris formed the moon and the rocky mantle melted as temperatures exceeded 2000° C
Organic (carbon-based) molecules formed from what kind of molecules?
inorganic molecules
What are two theories for how early organic molecules originated?
An extraterrestrial origin and an origin on early Earth
What is the extraterrestrial theory for the origin of early organic molecules?
Hundreds of thousands of meteorites and comets slammed into early earth; some may have carried organic materials.
Tagish Lake meteorite was found that 3% of its weight was organic matter.
What was the most abundant amino acid on the Tagish Lake meteorite?
Glycine
What is the early Earth theory for the origin of early organic molecules?
There was a reducing atmosphere at the time (high availability of hydrogen atoms & their electrons in the air). Due to this it would not have required as much energy to drive chemical reactions, making it easier to form the carbon-rich molecules from which life evolved
What is the Popular view for the composition of the early atmosphere?
Carbon dioxide (CO2).
Nitrogen gas (N2).
Water vapor (H2O).
Hydrogen gas (H2).
Other sulfur, nitrogen, and carbon compounds.
What was the Miller-Urey Experiment?
In 1953, Miller and Urey did an experiment that reproduced early atmosphere
Assembled reducing atmosphere rich in hydrogen with no oxygen gas.
Atmosphere placed over liquid water.
Temperature below 100° C.
Simulate lightning with sparks.
Found within a week that 15% of the carbon present as methane gas (CH4) converted into other simple carbon compounds
Compounds combined to form simple molecules and then more complex molecules.
Later experiments produced more than 30 carbon compounds including amino acids
Adenine also produced.
Concluded that key molecules of earth could have formed on early Earth
What are the two basic scenarios for the early evolution of central metabolism?
Autotrophic origin & Heterotrophic origin (this literally just means primitive organisms may have been autotrophic or heterotrophic)
What is the autotrophic scenario?
energy from the oxidation of inorganic compounds was used to drive a reductive version of the citric acid cycle
What is the heterotrophic scenario?
It builds on the Miller-Urey experiment which provides the source of a primordial soup in which life evolved.
Is it possible to distinguish between these two models? (autotrophic scenario & heterotrophic scenario)
No (the book doesn’t explain this and neither does the ppt. so lowkey just go with it)
Is it possible combine these two models? (autotrophic scenario & heterotrophic scenario)
Yes
What are the landmarks in the evolution of metabolism?
Oxygenic photosynthesis.
Carbon fixation.
Nitrogen fixation.
What is oxygen photosynthesis?
all molecular oxygen available today is the result of photosynthetic oxidation of water
there were two large pulses of oxygen into the atmosphere: one in the late Archaean and one in the late Proterozoic
Oxygenic photosynthesis became widespread in the late Archaean.
What is nitrogen fixation
reduced nitrogen is critical for life
nitrogen fixation can by volcanic action and lightening in the atmosphere but the modern enzyme nitrogenase (only found in prokaryotes) allows for nitrogen fixation to occur to be able to support large population of organisms
What is proposed to be the first genetic material and why?
RNA since it can catalyze chemical reactions and store genetic information
DNA later took over since it was more stable
Were single cells the first life forms?
Yes
constraining organic molecules to a physical space within a lipid or protein bubble could lead to what?
increased concentration of specific molecules which would then in turn lead to an increased rate of reaction involving these molecules
modern membranes are made of what?
a bilayer of phospholipids
early membranes are made of what?
fatty acids (more likely to form under prebiotic conditions: they have hydrophobic heads and hydrophilic tails so they could form bilayers like phospholipids)
Do we know exactly how cells formed and can we recreate that?
NAUR
The three monophyletic clades we call domains are descendants of what?
LUCA (last universal common ancestor)
What are Stromatolites?
mats of cyanobacterial cells that trap mineral deposits
Indirect evidence for ancient life
Oldest are 2.7 billion years old.
Modern forms are also known
Isotopic data can indicate that carbon fixation is an ancient process how?
Living organisms incorporate C12 into their cells before other carbon isotopes, they also have a higher level of C12 in their fossilized bodies than the nonorganic rock around them
