The Earth is estimated to be about 4. There is no doubt that in that very large amount of time, the Earth has undergone some drastic changes. This means that life on Earth has had to accumulate adaptations as well in order to survive. These physical changes to Earth can drive evolution as the species that are on the planet change as the planet itself changes.
The changes on Earth can come from internal or external sources and are continuing to this day. It may feel like the ground that we stand on every day is stationary and solid, but that is not the case. The continents on Earth are divided up into large "plates" that move and float on the liquid-like rock that makes up the mantle of the Earth. These plates are like rafts that move as the convection currents in the mantle move below them.
The idea that these plates move is called plate tectonics and the actual movement of the plates can be measured. Some plates move faster than others, but all are moving, albeit at a very slow rate of only a few centimeters, on average, per year.
This movement leads to what scientists call "continental drift". The actual continents move apart and come back together depending on which way the plates on which they are attached are moving. The continents have been all one big landmass at least twice in the history of the Earth. These supercontinents were called Rodinia and Pangaea. Eventually, the continents will come back together again at some point in the future to create a new supercontinent which is currently dubbed "Pangaea Ultima".
How does continental drift affect evolution? As continents broke apart from Pangaea, species got separated by seas and oceans and speciation occurred. Individuals that were once able to interbreed were reproductively isolated from one another and eventually acquired adaptations that made them incompatible. This drove evolution by creating new species. Also, as the continents drift, they move into new climates.
What was once at the equator may now be near the poles. If species did not adapt to these changes in the weather and temperature, then they would not survive and go extinct.
New species would take their place and learn to survive in the new areas. While individual continents and their species had to adapt to new climates as they drifted, they also faced a different type of climate change. The Earth has periodically shifted between very cold ice ages across the planet, to extremely hot conditions. These changes are due to various things such as slight changes to our orbit around the sun, changes in ocean currents, and the build-up of greenhouse gases such as carbon dioxide, among other internal sources.
No matter the cause, these sudden, or gradual, climate changes force species to adapt and evolve. Data from thousands of studies was assembled to paint a broad picture of biodiversity. Video: Andrew Zaffos and Shanan Peters. Scientists began to speculate about how these alterations would affect the formation and extinction of species and thus, what we call biodiversity. In , James Valentine and Eldridge Moores of the University of California suggested that broken-up continents would create more ecological niches and promote favorable climate and environmental conditions that are conducive to biodiversity.
In the Proceedings of the National Academy of Sciences this week May 15, , two University of Wisconsin—Madison geoscientists have plumbed some of the broadest databases in geology and paleontology to show that their predecessors were on the right track: Marine species tend to become more numerous when the continents divide, and to stabilize — maybe even decline — when continents congeal.
Their report focused on fossilized marine species in sedimentary rock, which are more numerous and easier to study than species that lived on land. The researchers created an index to show relative continental fragmentation and then compared that index to global fossil data in the Paleobiology Database. The result was as originally predicted, with a few twists.
During and after periods of fragmentation, marine diversity increases. During consolidation, the brakes seem to be put on diversification and marine biodiversity tends to plateau. The study was unable to determine exactly why the movement of continents affected biodiversity, but plate tectonics has both direct and indirect effects, Peters says.
Conventional ecological theory says that an isolated population will diverge from the original population, forming new species as organisms enter empty niches and as an increasing number of generations separate them from their common ancestor. This is one reason why modern islands have so many unique species. One of the elements lacking in the theory was the mechanism for how it works—why did the continents drift and what patterns did they follow?
Wegener suggested that perhaps the rotation of the Earth caused the continents to shift towards and apart from each other. It doesn't. Today, we know that the continents rest on massive slab s of rock called tectonic plate s.
The plates are always moving and interacting in a process called plate tectonics. The continents are still moving today. Some of the most dynamic sites of tectonic activity are seafloor spreading zones and giant rift valleys.
In the process of seafloor spreading , molten rock rises from within the Earth and adds new seafloor oceanic crust to the edges of the old. Seafloor spreading is most dynamic along giant underwater mountain ranges known as mid-ocean ridge s. As the seafloor grows wider, the continents on opposite sides of the ridge move away from each other. The two continents are moving away from each other at the rate of about 2.
Rift valley s are sites where a continental landmass is ripping itself apart. Africa, for example, will eventually split along the Great Rift Valley system. What is now a single continent will emerge as two—one on the African plate and the other on the smaller Somali plate.
The new Somali continent will be mostly oceanic, with the Horn of Africa and Madagascar its largest landmasses. The processes of seafloor spreading, rift valley formation, and subduction where heavier tectonic plates sink beneath lighter ones were not well-established until the s.
These processes were the main geologic forces behind what Wegener recognized as continental drift. The way some continents fit together like puzzle pieces inspired the theory of continental drift. Map by USGS. Alfred Wegener. Great Rift Valley system. Mid-Atlantic Ridge. Media Credits The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.
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