Changes in species over time

Question 1

Fossil record

Answer 1

Provide evidence of when organisms first appeared on earth, how species have changed and developed over billions of years, evidence of species that are extinct and how they gave rise to current species.

Question 2

Rock formation

Answer 2

• Strata (rock layers) are deposited over time as the weight of sediments on top of each other compresses the original sediment layer so that it becomes rock
• Over time the rock is eroded, uplifted through the movement of tectonic plates or excavated by palaeontologists so the fossil is exposed.
• Can be inverted or twisted by geological processes. Fauna and flora in sedimentary rock strata are arranged vertically in a consistent order which allows for the relative dates of appearance of species to be determined. This process takes millions of years.
  Principle of superposition states: Over long periods of time, sedimentation events result in layers of sedimentary rock. The lower layers of the rock are older whereas upper layers are younger.

Question 3

Fossil formation conditions:

Answer 3

• Die in: water, sedimentary rock, limestone, ash from a volcanic eruption, very cold environment (remains preserved by freezing)
• No exposure to oxygen (will decompose the specimen) eg. mud at bottom of a stagnant body of water.
• Contain hard body parts
• Left undisturbed for a very long time.

Question 4

Absolute dating of fossils

Answer 4

requires the knowledge of the half-life of a parental isotope (the time it takes to decay by half into a daughter element). From here the ratio of a radioactive parent isotope to a stable daughter element can be measured. Radioactive isotopes decay / lose radioactivity over time - the older the rock is, the less radioactive it is (process is used to date fossils 60 000 years and younger)

Question 5

Faunal fossil succession

Answer 5

Different kinds of organisms are found in rocks of particular ages and appear in a consistent order.
Therefore, fossils can be used to identify rocks of the same age, even if in different elevations and locations. The same order or rock can be found worldwide

Question 6

Index fossil

Answer 6

Similar fossils from separate locations can be used as index fossils to date geologic events.
Can provide evidence of the relative age of fossils from different locations and give an indication of their likely appearance and extinction dates

Question 7

Transitional fossil

Answer 7

Is one that has both primitive (old) and derived traits and therefore provides evidence that the ancestral species evolved to become a more modern species.

Question 8

Physical fossils

Answer 8

Remains of structures
- Mineralised fossils: the organic material of the structure is replaced by minerals.
- Fossil impressions: the organic matter has disappeared, but the organism has left an impression of its structure. Eg: leaves / stem plants decay away as rock has formed, leaving an exact impression (mould) - this may fill with another sediment making a cast
- Preserved organisms: Sometimes, an organism is completely preserved in a substance that allows for this type of preservation - includes amber, ice and tar.

Question 9

Trace fossils

Answer 9

Trace fossils are preserved evidence of the activities of organisms, such as footprints, tooth marks, tracks, burrows and coprolites

Question 10

Biosignatures

Answer 10

Is a physical or chemical sign preserved in minerals, rocks or sediments that can be inferred to be cellular or to have resulted from the metabolic activities of an organism.

Question 11

Macroscopic VS microfossils fossils

Answer 11

• Macroscopic fossils can be seen and studied with an unaided eye or very low magnification.
• Microfossils fossils require the use of either light or electron microscopy to visualise them and to identify the details of their shape

Question 12

Speciation

Answer 12

• The process of formation of a new species
  1. Variation of characteristics are present in a population
  2. Breeding population becomes isolated
  3. Different characteristics arise through random genetic drift, mutation and environmental pressures, leading to genetic divergence
  4. Natural selection favours some characteristics over others. These survivors reproduce and pass on favourable genes and features to offspring → frequency of these genes increase
  5. Isolated population over time is different, producing new species and can no longer interbreed with the original population

Question 13

Species

Answer 13

Must be able to produce fertile and viable offspring.

Question 14

Prezygotic isolation mechanisms

Answer 14

• Temporal isolation - one species may be active by day and the other active at night
• Geographic isolation - one species may live on a mountain top and the other in the valleys
• Behavioral isolation - one species doesn’t recognize signs of sexual readiness in another species / unable to perform the courtship ritual - can meet, but nothing happens
• Mechanical isolation - physical difference and can’t mate

Question 15

Post-zygotic isolation mechanisms

Answer 15

• Operate after mating and are due to chromosomal and chemical imbalances between the different species.
• Incompatibility of gametes - sperm cannot penetrate the outer coats of the egg, fertilisation does not occur
• Zygote mortality - fertilisation occurs but the zygote fails to develop
• Inviability of zygote - the zygote develops into an embryo but does not develop beyond that
• Sterility of hybrid - hybrid offspring survive but are sterile

Question 16

Allopatric speciation

Answer 16

When speciation occurs under circumstances where populations become geographically separate.
1. A single population is divided by a physical barrier to become geographically isolated. There is no gene flow between the populations.
2. 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.
3. If they cannot produce fertile viable offspring when brought together, they are reproductively isolated and are now two different species

Question 17

Galápagos finches

Answer 17

• Darwin’s famous deduction → finches living on each island were similar but different to each other, and so each finch had evolved from the ancestral finches that reached there from South America.
• The finches look different from each other (distinctively shaped beaks) because of the differing environmental selection pressures on each island based on food availability.
  The larger islands of have higher elevations, which allows large trees to grow
  The smaller islands have lower elevations and have vegetation of cacti and grasses.
• After the finches had arrived on an island, they became geographically isolated due to the surrounding ocean. Over time, allopatric speciation occurred.

Question 18

Sympatric speciation

Answer 18

Occurs when members of a population living in the same area diverge sufficiently to become two different species.
1. A single population is divided by prezygotic isolation barriers. Initially there is some gene flow between populations
2. Over many generations, genetic divergence occurs. The two palm trees produce flowers at different times of the year; therefore, there is no reproduction occurring between the two species. Eventually the isolated populations respond differently to environmental selection pressures, which leads to different phenotypes being selected for by natural selection or genetic drift.
3. When they can no longer reproduce fertile offspring when brought together they become two different species.

Question 19

Howea palms on Lord Howe Island

Answer 19

H. belmoreana
- Soil will only grow in volcanic soil
- Out competes H. forsteriana in a specific habitat and thus has a greater population size (3X) (higher pH in soil)
- Fowers 6-7 weeks later

H. forsteriana
- Soil generalist and will grow in both volcanic and calcareous soils
- Can live in a wider habitat, but H. belmoreana out compete it in volcanic soils (lower pH in soil)
- Flowers 6-7 weeks earlier

Groups become reproductively isolated because some members of population had varied flower time