Continental drift describes one of the earliest ways geologists thought continents moved over time. Today, the theory of continental drift has been replaced by the science of plate tectonics. The theory of continental drift is most associated with the scientist Alfred Wegener. In the early 20th century, Wegener published a paper explaining his theory that the continental landmasses were “drifting” across the Earth, sometimes plowing through oceans and into each other. He called this movement continental drift. Pangaea Wegener was convinced that all of Earth’s continents were once part of an enormous, single landmass called Pangaea. Wegener, trained as an astronomer, used biology, botany, and geology describe Pangaea and continental drift. For example, fossils of the ancient reptilemesosaurus are only found in southern Africa and South America. Mesosaurus, a freshwater reptile only one meter (3.3 feet) long, could not have swum the Atlantic Ocean. The presence of mesosaurus suggests a single habitat with many lakes and rivers. Wegener also studied plant fossils from the frigid Arcticarchipelago of Svalbard, Norway. These plants were not the hardy specimens adapted to survive in the Arctic climate. These fossils were of tropical plants, which are adapted to a much warmer, more humid environment. The presence of these fossils suggests Svalbard once had a tropical climate. Finally, Wegener studied the stratigraphy of different rocks and mountain ranges. The east coast of South America and the west coast of Africa seem to fit together like pieces of a jigsaw puzzle, and Wegener discovered their rock layers “fit” just as clearly. South America and Africa were not the only continents with similar geology. Wegener discovered that the Appalachian Mountains of the eastern United States, for instance, were geologically related to the Caledonian Mountains of Scotland. Pangaea existed about 240 million years ago. By about 200 million years ago, this supercontinent began breaking up. Over millions of years, Pangaea separated into pieces that moved away from one another. These pieces slowly assumed their positions as the continent we recognize today. Today, scientists think that several supercontinents like Pangaea have formed and broken up over the course of the Earth’s lifespan. These include Pannotia, which formed about 600 million years ago, and Rodinia, which existed more than a billion years ago. Tectonic Activity Scientists did not accept Wegener’s theory of continental drift. 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 massiveslabs of rock called tectonic plates. 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 ridges. As the seafloor grows wider, the continents on opposite sides of the ridge move away from each other. The North American and Eurasian tectonic plates, for example, are separated by the Mid-Atlantic Ridge. The two continents are moving away from each other at the rate of about 2.5 centimeters (1 inch) per year. Rift valleys 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 1960s. These processes were the main geologic forces behind what Wegener recognized as continental drift.
<span>Science affects society in a variety of areas, including basic ones like transport, industry, economy and technology. Throughout history, there have been multiple occasions on which science has had a profound impact on society.</span>
Interestingly, antibodies do not directly attach nor destroy any pathogens, rather they bind to pathogens and in doing so render them incapable of causing an immune response.
<h3>What are antibodies?</h3>
Antibodies are proteins that protect your body when an undesirable material enters it. Antibodies, which are produced by your immune system, attach to these harmful molecules and destroy them from your system. Immunoglobulin is another term for antibody.
When an antigen comes into touch with a B cell, it divides and clones the cell. Millions of antibodies are released into your bloodstream and lymph system by these cloned B cells, also known as plasma cells. Antibodies may be found in a variety of places throughout your body, including your skin, lungs, tears, saliva, and even breast milk.
According to Guinness World Records the Brazilian wandering spider (Phoneutria fera)
is officially the world’s most venomous spider. It is capable of
injecting a powerful neurotoxin which is nearly 20 times more deadly that of the Black Widow spider if it gets into the blood stream.
That is as potent as the venom of many deadly snake species and the
effects are similar. The symptoms of envenomation include a loss of
muscle control leading to breathing problems which can result in
complete respiratory paralysis and eventually asphyxiation.
But there are two other major side effects to the wandering spider’s
bite; firstly there is intense pain and secondly, if you happen to be
male there is the four hour hard on. Yes, you did read that correctly –
the bite of the Brazilian wandering spider can cause an erection that
lasts for several hours, unfortunately it is also painful.
In
addition to the this deadly venom the behaviour of the wandering spider
make it particularly dangerous to humans. As its name suggests the
spiders are not confined to a web in a dark corner. In fact they like to
turn up in all manner of hiding places; boots, piles of clothes, log
piles, cars and bunches of bananas. Also known as ‘banana spiders’
wandering spiders have been known to hitch a ride across the globe in
boxes of bananas. In one case a man in the UK was bitten after buying
bananas in his local supermarket.
There is little doubt that these
are dangerous spiders. Their aggressive nature and close contact with
humans have resulted in a number of deaths over the years. In one tragic
case a single spider was responsible for the deaths of two children
in São Paulo. Fortunately an effective antivenom has been developed and
there have been relatively few fatalities since.
