Topic 6 Flashcards
What influences the probability that an organism will become a fossil?
more likely if: hard (rather than soft-bodied), aquatic (not terrestrial), inshore marine (not offshore), decomposing organisms absent
How do we date fossils?
sedimentary stratigraphy
can’t tell how long ago fossil was created
but can tell which fossil came first, second, etc.
What is radiometric dating?
radioactive isotopes in fossils and rocks
decay of one isotopic form to another at a constant rate
example: C-12 and C-14 (plants take this up during photosynthesis, animals get it by eating plants)
What is half-life?
50% of atoms in a given amount of radioactive substance have decayed
What are plate tectonics and continental drift?
understanding history of Earth
land-masses drift around on plates “floating” on hot mantle
tectonic boundaries sites of earthquakes and volcanoes
relative locations of land-masses have changed over time
What are the consequences of continental drift?
changes to the environment and climate: opportunities for diversification of life, when land masses are isolated each can develop own suite of species, allopatric speciation
mass extinctions: when Antarctica drifted to the pole and froze solid
When did life begin?
stromatolites (3.5 billion years ago): rocks with distinctive layer structure
look identical to living mats of microbes
layers of microbes and sediment
top layer uses photosynthesis lower layers use top layer’s byproducts
What are the challenges to explain how life formed?
where did the organic molecules come from?
simplest form of life are complex?
how does chemistry become biology?
how did self replication begin?
What are the steps of the origin of life on Earth?
- Abiotic synthesis of organic molecules
- Abiotic synthesis of macromolecules
- Formation of protocells
- Self-replicating molecules
What is the first step in the origin of life on Earth; abiotic synthesis of organic molecules?
early Earth had a very different climate
experiments (1950’s) tried to replicate conditions
researchers were able to create amino acids
other sources: deep sea vents, meteorites containing amino acids, lipids, sugars, nitrogenous bases
What is the second step in the origin of life on Earth; macromolecules?
abiotic synthesis of macromolecules
RNA monomers produced spontaneously from simple molecules
experiments: polymers of small organic molecules produced by combining amino acids/nucleotides on hot sand, clay, or rock
What is the third step in the origin of life on Earth; formation of protocells?
life reproduces: DNA molecules carry genetic information
life requires energy: metabolism
needs to separate itself from the environment
cell membrane, but free-floating amino acids, proteins and nucleic acids would not have been able to behave like cells
What are protocells?
spontaneous formation of hollow lipid vesicles suggest how early cell-like structures may have arisen
sphere would have been able to keep (or export) own products
experiment showed that vesicles form faster in the presence of a type of volcanic clay thought ot be common 4 billion years ago
What is the fourth step in the origin of life on Earth; first nucleic acids?
first genetic material: RNA
form different shapes depending on environment, if favored by natural selection form “RNA” World
genetic material of all living things today: DNA
more accurately replicated (also favored by natural selection)
Where did life originate?
hot, mineral-rich deep-sea vents
where many of the earliest derivative prokaryotes (archaea) still live
experiments mimicking charcateristics of underwater volcanoes produce more amino acids than those not mimicking them
