The History of Life Flashcards
4.6 BYA
Sun and Planets Form
4.6 - 3.9 BYA
Meteoritic bombardment and volcanic activity create reducing atmosphere
by 3.9 BYA
reducing atmosphere(high in hydrogen content, no free oxygen, thick with water vapor)
- H2O, CO2, CO, CH4, NH3, H, etc
3.9 BYA onwards
first cells appear
Steps from Inorganic to Cells
- Abiotic synthesis of small organic molecules.
- Single molecules(monomers) join with other molecules to produce polymers.
- Self replication.
- Polymers and monomers packed into a cell-like structure.
- Abiotic synthesis of simple organic molecules(monomers)
PROBLEM: Early scientists assumed that organic molecules are formed only by organic life.
SOLUTION: inorganic chemistry found to create organic compounds.
- Miller/Urey Experiments
- recreated early earth atmosphere in lab
- formed Amino Acids withing a few weeks.
- Hydrothermal Vents
- localized reducing environments still possible today
- made possible life on earth without sunlight
o chemosynthesis uses Methane and Sulfur to create glucose
- localized reducing environments still possible today
- Extraterrestrial origins
- A nebula is an accumulation of gas and dust in space
o 10-15% is organic molecules so it actually is potential
- Meteorites actually contain amino acids
- Monomers to Polymers
PROBLEM: Complex polymers are generally created via organic enzymatic processes
SOLUTION: Clay minerals facilitate polymer formation
- Lattice structure
- Can behave like an enzyme under specific conditions
- Protects against UV(breaks down organic molecules)
- Self-replicating hereditary material
PROBLEM: DNA needs enzymes to replicate
SOLUTION: RNA- the original unit of heredity
- Self replicates
- Acts as own enzyme during replication
- Genetic material AND an enzyme - Self splices
- Catalyzes
- Possess a phenotype and genotype
- Protobiont
aggregate of abiotically produced organic
molecules suorrounded by membrane-like structure
- Can abiotically create a membrane with organic molecules in it
PROBLEM: Cell membranes associated w/ organic molecules derived from other organic cells
SOLUTTION: Several “cell-like” structures form abiotically that can self-replicate and metabolizes.
- Coacervates
- Can self replicate and metabolize
- Not technically alive but are organic - Liposomes
- Lipid bi-layer vesicles formed abiotically.
- Clay is vital in these processes
Protobiosphere
- Multiple protobiont lineages may have independently evolved
- Competition among lineages
- Lineages evolve
- Xna->rna->dna - Only one lineage remains today.
First cells appear
3.9 - 3.5 BYA
First cells were chemoautotrophs
chemoautotrophs rely on chemosynthesis to produce glucose from chemicals, such as
a. Sulfur (found at hydrothermal vents) b. Methane (found at cold seeps)
- Still exists today
The first photoautotrophs
Stromatolites (3.5 BYA) - rock like structures comprised of layering photosynthetic bacteria and sediment over time
a. oldest known fossils that formed ~3.5 billion years ago
Very rare now
o Some still off the coast of Australia
The Oxygen Revolution
Stromatolites create an oxygen rich atmosphere(byproduct of photosynthesis)
- Oxygen toxic to most existing prokaryotes
- Fundamental change to the chemistry of life on earth
- The “oxygen revolution” - Aerobic metabolism spreads
a. aerobic metabolism produces ~19 times > ATP than anaerobic
From Prokaryote(without organelles) to Eukaryote(membrane bound organelles)
Creates a new ecological niche of heterotrophs
The Endosymbiotic model (Lynn Margulis)
- Prokaryotic cell engulfs another prokaryotic cell but they live symbiotically with each other creating Eukaryotes - Mitochondria is an example of this
The three domains of life
established by 2.1 BYA
- Bacteria(prokaryote)
- Archaea(prokaryote)
- Eucarya(Eukaryote)
- Have a common ancestor but branched since then
From single cell to multicellular Eukaryote
- Evolves multiple times
- Independently in plants, fungi, and animals
- Oldest multicellular lineage ~ 1.5 BY old
- Allows for the evolution of cellular specialization (i.e. tissues)
Geologic Time
3 main eons
- Archaean 4.5 BYA – 2.5BYA
- Proterozoic 2.5 BYA – 540 MYA
- Phanerozoic 540 MYA - present
Archaean Eon
4.5 BYA - 2.5 BYA
- 4.5 - 3.9 BYA – First cells
- 3.9-3.5 BYA – First prokaryotes
- 3.5 BYA – First fossil evidence of phototrophic autotrophs
- 2.7 BYA – Oxygen Revolution
Proterozoic Eon
2.5 BYA - 540 BYA
- 2 BYA – Eukaryotes
- 1.5 BYA – Multicellularity first evolves
- ~700 MYA – first animals
Phanerozoic Eon
540 MYA - Present
Paleozoic Era(Explosion of Animal Diversity) 550 MYA - 251 MYA
- Cambrian Explosion
Periods:
Cambrian(oldest)->Ordovician->Silurian->Devonian->Carboniferous->Permian(youngest)
Mesozoic Era (age of dinosaurs) 250 MYA - 65.5 MYA
Periods:
Triassic(oldest)->Jurassic->Cretaceous(youngest)
Cenozoic Era (age of mammals) 65.6 MYA - Present
– last major extinction 65MYA
Periods:
Paleogene(oldest)->Neogene->Quaternary(youngest)
Plate Tectonics - dynamic earth
Pangea (Paleozoic) 251 MYA
Gondwana (Mesozoic) 135MYA
Laurasia (Mesozoic) 135MYA
Cenozoic(present earth) 65.6 MYA
Plates associated with geological activity
Mass Extinctions
Five major mass extinctions at beginning of Paleozoic, Mesozoic and Cenozoic eras (other minor mass extinctions occurred)
Probable cause of Cenozoic extinction – meteorite impacting Yucatan Peninsula
- 65 MYA
- Changed atmospheric conditions and brought mammals to the forefront
5 major mass extinctions
most recent 65 MYA
Coacervates
- Can self replicate and metabolize
- Not technically alive but are organic
