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Origins of Earth:
- Oldest rocks are > 4 billion years old.
- Surface waters stabilized into oceans.
- Surface and atmosphere had N2, CO2, HCN, N3, and H2O, but little O2.
- O2 is destructive to bonds in organic molecules.
- The young sun gave off less energy than now.
- Earth's climate was cold.
The Geologic Record:
- The fossil records reveals changes in the history of life on earth.
- Sedimentary rocks are deposited into strata and are rich sources of fossils.
- Few individuals have fossilized, and even fewer have been discovered.
Why is the Fossil Record Biased?
- Species that are most likely to of fossilized must have:
- Existed for a long time
- Were abundant and widespread
- Had hard body parts
Reveals the relative ages of fossils.
- Determines the absolute age.
- Parent isotope decays to Daughter isotope at a constant rate.
- Each isotope has a known half-life.
For older fossils, date sedimentary rock layers above and below the fossil.
Why are Radioisotopes not Measured Directly from Sedimentary Rocks?
The sedimentary rocks are debris from upstream which predate the fossil.
Magnetism of Rocks:
- Can provide dating information.
- Reversals of the magnetic poles leave their record on rocks.
Major Boundaries Between Geological Divisions:
Correspond to extinction events in the fossil record.
Origin of Life:
- May have begun earlier; even before the atmosphere stabilized
- May have been destroyed several times.
- Did not use to transform energy.
- May have released methane (CH4).
May have warmed the climate via the greenhouse effect.
The warming of the atmosphere by energy(heat) that entered via sunlight and cannot escape due to some sort of barrier(CH4).
First Single-celled Organisms:
- Oldest known fossils were stromatolites.
- Rock-like structures composed of many layers of bacteria and sediment.
Earth's sole inhabitants from 3.5 to about 2.1 billion years ago.
- Probably from cyanobacteria.
- Added oxygen(O2) to the atmosphere and water.
- Most atmospheric O2 is of biological origin.
The Oxygen Revolution:
- Rising O2 levels poisoned many kinds of early life.
- Other bacteria began using O2 in their metabolism.
- O2 reacted with dissolved iron and precipitated out to form banded iron formations.
The First Eukaryotes:
- Evolution of eukaryotic cells allowed for a greater range of unicellular forms.
- Eukaryotes: true nucleus, membrane bound organelles, bigger(more complex) than Prokaryotes
Origin of Multicellularity:
- Diversification occurred when multicellularity evolved.
- Gave rise to algae, plants, fungi, and animals.
- The oldest known fossils are small algae.
- Sudden appearance of fossils resembling modern phyla.
- Provides the first evidence of predator-prey interactions.
- More complex interactions between species.
- Atmospheric oxygen levels increasing.
- Had a long fuse.
How Could Increased O2 and Greater Complexity in Interactions Increase Diversity?
- Mobility allows for more interactions(predator/prey)
- More oxygen = can disperse easily
- Evolution from predator/prey scenario
- Presence of hardy body increased (more fossils)
Colonization of Land:
- Plants and fungi likely colonized land together.
- Arthropods and tetrapods are the most widespread and diverse land animals.
- Tetrapods evolved from lobe-finned fish.
- Most species that have ever lived are now extinct.
- Rate of extinction has increased dramatically and caused a mass extinction periodically.
- In each mass extinction events, more than 50% of Earth's species became extinct.
When did each of Mass Extinction take place?
At the end/start of a period
Mass extinction on Ecology:
- Alter ecological communities and the niches.
- Takes 5 to 100 MY for diversity to recover.
- Can pave way for adaptive radiations.
Evolution of diversely adapted species from common ancestor upon a new environmental opportunity.
- Continents move slowly through the process of continental drift.
- The supercontinent is called Pangaea.
Consequences of Continental Drift to Life.
- Forces life to adjust to changing environments.
- Previously attached continents may share similar species.
The Chemical Origin of Life:
- Life began synthetically (chemicals).
- Life continues from pre-existing life (natural).
- Louis Pasteur experiments.
Four potential steps:
- Abiotic synthesis of monomers.
- Monomers joining together to form macromolecules.
- Origin of self- replicating molecules (enabling inheritance).
- Packaging into membrane-enclosed protobionts.
Miller and Urey Experiment (1953):
- Tried to recreate the conditions of early Earth.
- Organic molecules formed.
- May not have been done correctly.
- But experiments produced 20 amino acids, sugars, lipids, and some nucleotides.
What Types of Reactions Produce Polymers?
Chemical reactions occur if dilute monomer solutions drip onto hot rocks or sand.
Certain Substances Increase Reaction Rates:
- Clays have charged regions that bind amino acids and hold them close together.
- Some metals (iron in pyrite) act as catalysts.
The Origin of Genetic Information:
- Flow of information: DNA > RNA > protein
- RNA may have come first.
- Short pieces of RNA can be made naturally.
- RNA is autocatalytic - replicating.
- RNA binds to amino acids and helps them join.
- DNA is more complex and may have developed later.
- Protobionts = pre-cells
- Can be made abiotically (lipids in water).
- Show growth, splitting, and engulfment.
- oShow membrane potentials and excitability.
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