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