D.The geological time scale.
The correct answer is B. Climate.
Plate tectonics is a theory that suggests that parts of the outer surface of the earth, the lithosphere, form plates that are able to move since they sit on top of a molten rock layer.
This layer they sit on is called the asthenosphere. Motion is particularly pronounced where the lithosphere and asthenosphere meet. Much tectonic activity occurs at these boundaries including volcanoes, earthquakes, and the formation of mountains.
The motion of plates means that they will move to areas where the climate is different. In other words, plate tectonics influences organic evolution because of the climate. When living organisms are exposed to different climatic conditions, they develop adaptations. Over time this can cause the population to evolve.
Climate impacts the distribution of vegetation, which then, in turn, influences the distribution of the animal population. In fact, climatic factors such as amount and availability of precipitation and the range of temperatures affect entire ecosystems.
The plate tectonics theory is really the idea that the earth’s crust consists of plates of lithosphere that are atop a layer of molten rocks that allow for movement.
This theory developed after many years and many scientific observations. In fact, plate tectonics eventually grew from the idea of continental drift which was put forth in 1912.
History of the theory
In the 1700s, Alexander von Humboldt suggested that the continents must have been joined at some stage because of similarities that were evident.
However, it was not until 1912 that the idea of continental drift was suggested. This theory was developed by Alfred Wegener and was to form the foundation for the development of plate tectonic theory later on.
Wegener used evidence to support the idea of continental drift; For instance, the presence of the same fossils and rocks on neighboring continents, and the similarities in palaeoclimate on continents now separated by an ocean.
Although this evidence was compelling for the idea that continents were once connected, Alfred Wegener was unable to provide a good mechanism for how exactly they moved apart. In later years, Holmes came up with the idea that the movement of plates was due to convection in the earth.
Discovery of features on the ocean floor provided more evidence that the earth’s crust did indeed move. Henry Hess suggested in 1960 that convective flow of the mantle caused the formation of oceanic trenches and ridges. This was really the origin of the theory of seafloor spreading.
Plate tectonics and evolution
The movement of continental plates led to changes in climatic conditions on the respective continents. As the plates moved to new areas of the earth, continents became exposed to different conditions.
Climate is different at different latitudes of the earth due to patterns of global air circulation. It is easy to envision that the climate would have changed when plates moved to different latitudes. This climatic change would have had an impact on the species that were present on the particular plate that was involved.
Organisms are uniquely adapted to the conditions in the environment that they occur in and may not be easily able to adapt to a changing climate. In fact, the pace at which the climate changes may be important in determining which species can adapt quickly enough.
A population which cannot adapt and is not able to move out of an area may very well go extinct. Other species which can adapt then would be able to do so, and over time the characteristics of the species would change.
Selection and speciation
Climate acts as an agent of selection on species populations. Many aspects of an organism’s life are dependent on climate. The timing of life cycles is one such factor, in both plant and animal species.
Animals often depend on the life cycles of plants. For example, bees depend on flowers for pollen and many species of birds rely on fruits produced by plants. This means that changes in the timing of flowering and fruit formation can be expected to also impact the animal populations.
Natural selection is the process by which the organisms with the genotype that is most likely to survive, will survive to reproduce. This means of course that over time this preferred genotype becomes more frequent in the population.
This eventually then can lead to evolution, which is simply a change in the population over generations. Over time new species may evolve as populations change.
Another result of plate tectonics was probably allopatric speciation. This is when a population becomes separated geographically from another population, resulting in new species being formed.
If one plate becomes completely separated from another by the ocean, then a population will split into two and allopatric speciation can occur.
Example of climate causing evolution
Researchers were able to record evolution in Darwin’s finches on the Galapagos Island. This occurred in response to a rare El Niño event that happened in 1982 to 1983, in which rainfall dramatically increased.
The change in weather caused a change in food with more plants that produced small seeds being present than plants that produced large seeds. As a result, finches having a small beak size were selected for, and this was evident in the next generations of the species concerned.
Changes in the climate on the island led to changes in the plants which of course then resulted in changes in the birds. This research is used as direct evidence of a case of evolution in response to a climatic event.
Many scientists are concerned that global warming could lead to radical changes in the species present today. Species may go extinct, distribution ranges may change and new species may form as the earth heats up.
Scientists have already noted changes in gene frequencies in the tree Fagus sylvaticus in response to changing temperatures over the second half of the 20th century.
Since climate is so impactful on species, researchers and conservationists are concerned that some species may become extinct due to the increase in global temperatures.
- BR Grant, PR Grant (1993). Evolution of Darwin’s finches caused by a rare climatic event. Proceedings of the Royal Society of London B.
- AS Jump, JM Hunt, JA Martinez-Izquierdo (2006). Natural selection and climate change: temperature‐linked spatial and temporal trends in gene frequency in Fagus sylvatica. Molecular Ecology.
- J Merilä (2012). Evolution in response to climate change: in pursuit of the missing evidence. BioEssays.
- JB Murphy, TH van Andel (2018). Plate tectonics. Retrieved from Encyclopedia Britannica.
- RL Dorit, WF Walker, RD Barnes (1991). Zoology. Philadelphia: USA, Saunders College Publishing.