chapter eight: changes in species over time Flashcards
timeline showing the order in which the following groups evolved in
- prokaryotic cells
- photosynthetic organisms
- multicellular organisms
- plants
- fish
- amphibians
- reptiles
- dinosaurs
- birds
- mammals
- insects
- flowering plants
- primates
identify the conditions that favour fossilisation
- low oxygen levels
- low temperatures
- protected from scavengers
explain how fossils can form
- an organism dies
- the organism is buried immediately (rapidly)
- protected from scavengers
- prevented from decomposition by low oxygen levels and low temperature
- over time, the molecules in the organisms are replaced by minerals from groundwater
compare mineralised, mold, cast and trace fossils
mineralised fossils
- form when hard structures are replaced by minerals
mold fossils
- form when a petrified fossil dissolves and leaves an impression of the original
- these can be filled in to make cast fossils
cast fossils
- form when they are filled in molds
trace fossils
- form when traces of activity are buried before they are erased and turn into rock
define the law of fossil succession
fossils are used to identify rocks of the same age - fossils found in the same layer as rock formed at the same time
- different kinds of organisms do not occur randomly in the fossil records but are found only in rocks particular ages and appear in a consistent order
based on the law of fossil succession (older fossils are in lower rock)
describe the features needed for a species to be used as index fossils
index fossils must be
- abundant
- distributed worldwide
- existed for only a short period of time
- found in restricted depths of rock strata
how are index fossils used in relative dating
index fossils can be used to determine the relative ages of rock strata anywhere in the world
- index fossils are of organisms that were common throughout the world for a limited geological time
describe the importance of transitional fossils such as archaeopteryx in identifying the timeline of evolution
transitional fossils can tell us about major changes - evidence of evolution
- transitional fossils remains of a life form that exhibits traits common to both an ancestral group and its derived descendants group
- e.g. archaeopteryx shows characteristics presence of feathers and a wishbone, however it also showed some reptilian features not lost in modern birds. (they were also not capable of the magnificent flight of modern birds)
describe how the law of fossil succession allows relatives dating to occur
older fossils have to be below younger fossils within the strata
- if you find a fossil below, it must be older
describe how co-paring the ratio of carbon-14 to carbon-12 can indicate the time an organism died
the more carbon-12 in an organism, the more time has passed since the organism has died
- the more half-lives there are, the more time has passed (each substance has a different half-life time)
define half life
the time taken for the radioactivity of a specified isotope to fall to half its original value.
define species
a group of organisms that can reproduce with each other in nature and can produce fertile offspring (exchanging genes)
describe the process of allopatric speciation (include gene flow)
allopatric speciation is when populations are geographically seperate
- populations are geographically separated by a physical barrier
- there is no gene flow between populations, resulting in the populations to begin to experience genetic divergence such as through mutation
- over many generations, the isolated populations are subjected to different environmental selection pressures, which leads to different phenotypes being selected for by natural selection or genetic drift
- may evolve to become so different that if individuals from the daughter population meet they would no longer mate or produce fertile offspring
- now there are two distinct gene pools and different species
give examples of isolating mechanisms
isolation mechanisms: something that stops one species from breeding with each other
- geographical barriers (mountains or different environment)
- temporal isolation (different mating seasons)
- mechanism isolation (things that prevent a species from breeding with another)
describe how the Galapagos finches diverged into 13 seperate species
- Galapagos islands have variety of habitats - arid regions and mountainous regions
- differing environmental selection pressures on each of the islands based on food availability (main environmental pressures) resulted in change in the beak space due to the different food source and diet
- after the finches had arrived on an island they become geographically isolated due to the surrounding ocean hence over time allopatric speciation occurs
- their beak shape evolved rapidly by allopatric speciation
what is sympatric speciation
speciation without the presence of a geographic barrier where different species arises within the same population
- new species arise without a physical barrier
- both species share the same ancestor
- they are both found/evolve in the same location from a common ancestor but are considered different
- PRE-ZYGOTIC ISOLATION - THEY CANNOT MATE
describe the process of sympatric speciation
- the initial population has variation
- Then there is a change that starts to separate the time of breeding
- over time, that becomes bigger so that it is a discrete breeding time between both groups
explain why sympatric speciations are rare
- it doesn’t happen very often
- It is not likely that groups living closely together will evolve differently from each other
- gene flow can still occur
- genetic drift has less of an impact
- less likely to be isolated
summarise the events that led to different species of Howes palms in the same area
- both species of Howes palms share the same ancestor
- both found in the same location from a common ancestor
- barrier resulting from the dirt they grow in
- the soil leads the plants to flower at different time
- over time, flowering times changed to have no overlap therefore they cannot reproduce
what evidence is there for evolution?
- fossils
- biogeographic distribution
- comparative (anatomy, embryology, DNA)
define speciation
the process of new species arising/the formation of a new species
process of speciation
- population has variation
- populations are isolated/is split by a physical/geological barrier, by preventing gene flow
- different conditions (selection pressures) occurs on each side
- different adaptations arises one each population
- they are now different species and cannot breed
what evidence do vestigial structure provide for evolution
- they indicate the relatedness between species
- the structure are similar, indicating that species share and have evolved over time from a common ancestor, however, the structures were once functional in the ancestors
what is a common ancestor
- is a species that existed earlier in the fossil record
- evolved into two or more different species
- an ancestor shared by later species
