26 Flashcards
geologic events that alter environments
change the course of biological evolution
scientific evidence is accumulating that chemical and physical processes on early earth, aided by the emerging force of selection, produced very simple cells thru a sequence of 4 main stages:
1) abiotic synthesis of small organic molecules (ex: amino acids and nucleotides)
2) the joining of these small molecules (monomers) into polymers (ex: proteins and nucleic acids)
3) the packaging of these molecules into protobionts
4) the origin of self-replicating molecules that eventually made inheritance possible
protobionts
droplets with membranes that maintained an internal chemistry different from that of their surroundings
aggregates of abiolotically produced molecules surrounded by a membrane or membrane-like structure
earth and the other planets of the solar system formed about
4.6 billion years ago
how did earth and th eother planets of the solar system form
they condensed from a vast cloud of dust and rocks that surrounded the young sun
its unlikely that life could’ve originated or survived on earth for the first few hundred miliion years b/c
the planet was still being bombarded by huge chunks of rock and ice left over from the formation of the solar system. these collision generated enough heat to vaporize all the available water and prevent seas from forming. this phase stopped 3.9 bill years ago
oldest known rocks on earth’s surface
Issua in Greenland. 3.8 billion years old
atmospheric conditions of early Earth
thick w/ water vapor, along w/ various compounds released by volcanic eruptions, including nitrogen and its oxides, carbon dioxde, methane, ammonia, hydrogen, and hydrogen sulfide
as earth cooled,
the water vapor condensed into oceans, and much of the hydrogen quickly escaped into space
Oparin-Haldane hypothesis
1920s - postulated that earth’s early atmosphere had been a reducing (electron-adding) environment, which organic compounds could’ve formed from simple molecules
what provided the energy for the organic synthesis described by the Oparin-Haldane hypothesis?
lightning and intense UV radiation
haldane suggested that
the early oceans were a solution of organic molecule, a “primitive soup” from which life arose
it’s unclear whether young Earth’s atmosphere contained enough __ and __ to be reducing
methane and ammonia
growing evidence suggests that the early atmosphere was made up primarily of __ and __ and was neither __ nor __
nitrogen and carbon dioxxide;
reducing nor oxidizing (electron-removing)
it is likely that small “pockets” of the early atmosphere, perhaps near ___, were reducing
volcsubmanic openings
instead of forming in the atmosphere, the first organic compounds on earth may have been synthesized
near submerged volcanoes and deep-sea vents, weak points in earth’s crust where hot water and minerals gush into the ocean
submerged volcanoes and deep-sea vents are rich in
inorganic sulfur and iron compounds, which are important in ATP synthesis by present-day organisms
some of the organic compounds from which the first life on earth arose may have come from space b/c
among the meterorites that land on earth are carbonaceous chondrites
carbonaeceous chondrites
rocks that are 1-2% carbon compounds by mass
life is defined partly by 2 properties
accurate replication and metabolism
role of metabolism
it provides an elaborate enzymatic machinery necessary for the replication of DNA. it also provides a copious supply of nucleotide building blocks
protobionts exhibit
some of the properties associated w/ life, including simple reproduction and metabolism
laboratory experiments demonstrate that protobionts couldve formed spontaneously from
abiotically produced organic compounds
liposomes
small membrane-bounded droplets
describe liposomes formation
they form when lipids or other organic molecules are added to water. the hydrophobic molecules in the mixture organize into a bilayer at the surface of the droplet, much like the lipid bilayer of a plasma membrane
b/c the liposome bilayer is selectively permeable,
liposomes undergo osmotic swelling or shrinking when placed in solutions of different solute concentrations
some liposomes store energy in the form of
a membrane potential – a voltage across the surface
some liposomes can discharge their voltage in
nerve cell-like fashion
the 1st genetic material was
RNA, not DNA
RNA, which plays a central role in ______, can also carry out ______
protein synthesis;
a number of enzyme-like catalytic functions
ribozyme
enzyme-like RNA molecule that catalyzes reactions during RNA splicing
the best index fossils for correlating strata that are far apart are
the shells of marine organisms that were widespread
index fossils
similar fossils, the presence of which can be used to correlate the strata at one location with strata at another location
index fossils reveal that
at any particular location there are likely to gaps in the sequence
why is it likely that at any particular location there are likely to be gaps in the fossil sequence?
that location may have been above sea level during certain periods, and thus no sedimentation occurred; or some of the sedimentary layers that were deposited when the location was submerged may have eroded away
