chapter twenty-five Flashcards
what types of changes does the fossil record show?
macroevolutionary changes
1. emergence of terrestrial vertebrates
2. impact of mass extinctions
3. origin of flight of birds
what did earth’s early atmosphere likely contain?
water vapor and chemicals released by volcanic eruoptions
what did chemical/physical processes on earth potentially produce?
simple cells
how were simple cells maybe produced?
- abiotic synthesis off small organic molecules
- joining of these small molecules into macromolecules
- packaging of molecules into protocols
- origin of self-replicating molecules
what did Oparin and Haldane hypothesize in the 1920s?
that the early atmosphere was a reducing environment
Miller and Urey 1953
- conducted lab experiments that showed the abiotic synthesis of organic molecules in a reducing environment (with pond and clay) is possible
- evidence not yet convincing there was reducing atmosphere
- organic molecules could have been formed with various possible atmospheres
where might the first organic compounds have been synthesized?
near volcanoes and deep sea vents
what have been found in meteorites?
amino acids
what were produced spontaneously from simple molecules
RNA monomers
when do small organic molecules polymerize
when concentrated on hot sand, clay, or rock
protocells - simple cells
fluid-filled vesicles with membrane-like strcuture
what are key properties of life that may have appeared together?
replication and metabolism
how are vesicles formed?
in water, lipids and other organic molecules can spontaneously form vesicles with a lipid bilayer
- adding clay can increase rate of vesicle formation
first genetic material
most likely RNA
ribozymes
RNA molecules that have been found to catalyze many different reactions
- can make complementary copies of short pieces of RNA
what has natural selection produced?
self-replicating RNA molecules
what types of RNA would have left the most descendent RNA molecules
RNA molecules that were more stable or replicated more quickly
RNA world
small RNA molecules able to replicate and store genetic info about vesicles that carried them
vesicles with RNA capable of replication would have been _____________
protocells
RNA could have provided the template for what?
DNA - more stable genetic material
richest source of fossils
sedimentary rock, deposited into layers called strata
fossil record is biased in favor of species that:
- existed for long time
- were abundant and widespread
- had hard parts
relative age of fossils
revealed by strata
absolute age of fossils
determined by radiometric dating
- parent isotope decays to daughter isotope at constant rate
- can be used for fossils up to 75,000 years old
half-life
time required for half of parent isotope to decay
if fossils are older than 75,000, how can they be dated?
isotopes can date the sedimentary rock layers above and below the fossil
what group to mammals belong to?
tetrapods
what is the geologic record divided into?
Hadean, Archaean, Proterozoic, Phanerozoic
which eon encompasses most multicellular eukaryotic life?
Phanerozoic
3 eras of phanerozoic
Paleozoic, Mesozoic, Cenozoic
what do major boundaries between geological divisions represent?
extinction events
stromatolites
oldest known fossils
- rocks formed by the accumulation of sedimentary layers on bacterial mats
when were stromatolites dated back to?
Archaean eon
when were prokaryotes earth’s sole inhabitants?
2.1-3.5 billion years ago
most atmospheric oxygen is of what?
biological origin
O2 was produced by what?
oxygenic photosynthesis, which reacted with dissolved iron and precipitated out to form banded iron formations
oxygen revolution
- caused extinction of many prokaryotic groups
- some groups survived/adapted using cellular respiration
what was the early rise in O2 likely caused by?
ancient cyanobacteria
what was the later increase of O2 maybe caused by?
evolution of eukaryotic cells containing chloroplasts
when were the oldest fossils of eukaryotic cells dated back to?
Proterozoic eon
what do eukaryotic cells have
nuclear envelope, mitochondria, endoplasmic reticulum, cytoskeleton
endosymbiont theory
mitochondrion and plastids (chloroplasts and related organelles) were formerly small prokaryotes living within larger host cells
endosymbiont definition
cell that lives within a host cell
key evidence for endosymbiont theory:
- inner membranes similar to plasma membranes of prokaryotes
- division similar to prokaryotes
- transcribe and translate their own DNA
- ribosomes more similar to prokaryotic ribosomes
oldest known fossils of multicellular eukaryotes
small algae
snowball earth hypothesis
periods of extreme glaciation confined life to equatorial region or deep sea vents
Cambrian explosion
sudden appearance of fossils resembling modern animal phyla in Cambrian period
what phyla appeared before the Cambrian explosion?
sponges, cnidarians, molluscs
what does the Cambrian explosion provide the first evidence of?
predator/prey interactions
vascular tissues in plants
transport material internally
what did plant and fungi form?
mutuals beneficial associations
- likely colonized together
most widespread and diverse animals
anthropoids and tetrapods
what did tetrapods evolve from?
lobe-finned fish
supercontinent
Pangea - could have been formed in 3 points in time
plate tectonics
earth’s crust is composed of plates floating on earth’s mantle
continental drift
tectonic plates moving slowly
what do interactions between plates cause?
formation of mountains, islands, and earthquakes
possible effects of Pangea
- deepening ocean basins
- reduction in shallow-water habitat
- colder/drier climate inland
what did the separation of land masses lead to?
speciation
mass extinction
where global environmental changes lead to increased rate of extinction
how many mass extinctions have there been
5
- in each one, more than 50% of species became extinct
Permian mass extinction
- boundary between Paleozoic and Mesozoic
- 96% of marine animal species
factors contributing to Permian extinctions
- intense volcanism in now Siberia
- global warming resulting from emission of large amounts of CO2 from volcanoes
- reduced temperature gradient from equator to poles
- oceanic anoxia from reduced mixing of ocean waters
Cretaceous mass extinction
- separates Mesozoic/Cenozoic
- half of marine species, plants/animals, dinosaurs
what evidence suggests a meteorite impact?
presence of iridium in sedimentary rocks
what can mass extinctions alter?
- ecological communities/niches
- percent of marine predators increased
adaptive radiation
evolution of diversely adapted species from common ancestor
- can occur when organisms colonize new environments with little competition
what might adaptive radiations follow?
- mass extinctions
- evolution of novel characteristics
- colonization of new regions
what did the disappearance in dinosaurs lead to?
expansion of mammals in diversity and size
development genes
control rate, timing, and spatial pattern of changes in an organism’s form as it develops into an adult
heterochrony
evolutionary change in rate/timing of developmental events
- can have impact on body shape
paedomorphosis
rate of reproductive development accelerates compared with somatic development
- sexually mature species may retain body features that were juvenile structures in ancestral species
homeotic genes
determine basic features
- where wings/legs develop on bird, or how flower’s parts are arranged
Hox genes
class of homeotic genes that provide positional info during development
- if expressed in wrong location, body parts can be produced in wrong location or alter timing
what do new morphological forms likely come from?
gene duplication events that produce new developmental genes
what do changes in morphological forms likely come from?
changes in REGULATION of developmental genes rather than changes in sequence of developmental genes
evolution is like what?
tinkering
how have complex eyes evolved?
from simple photosensitive cells independently many times
exaptations
structures that evolve in one context but become co-opted for a different function
