Download GRAĐA ZEMLJE

GRAĐA ZEMLJE
Seizmički valovi koji putuju
kroz unutrašnjost Zemlje
P (primarni) valovi – kompresijski,
longitudinalni; 4-7 km/s; prolaze
kroz čvrstu stijenu i kroz fluid.
S (sekundarni) valovi – transverzalni;
2-5 km/s; prolaze samo kroz čvrstu
stijenu.
Površinski seizmički
valovi
Konvergentne granica ploča
• Ocean-ocean konvergencija
• Ocean-kontinent konvergencija
• Kontinent-kontinent konvergencija
Ocean-ocean konvergencija
Ocean-kontinent konvergencija
Kontinent-kontinet
konvergencija
3.3 Billion Years Ago?
We know very little about the first continent (though, not exactly super, since there wasn't
much land in those days), so the shape, size and scale of the theorized Vaalbara is pretty
speculative. The two oldest cratons on the planet both have the oldest rock dated, so
assumptions are made about what Vaalbara might have looked like based only on these two
patches of oldness. It's named for the 'Brangelina' style mashup of the two cratons: the
South African Kaapvaal Craton and the Australian Pilbara Craton. Paleomagnetic data from
both these areas show that these two cratons could have been from the same
supercontinent.
The same evidence that shows the possible existence of Vaalbara also indicates that it
started to break up after 2.5 billion years.
3 Billion Years Ago
Ur is the first definitively known continent, despite being smaller at the time than Australia is
now. Because it was the only one at the time, and because Vaalbara is still a theory, Ur is
considered to be the first "super"continent. Ur would eventually join up with the continents
Nena and Atlantica about one billion years later to form the supercontinent Rodinia. Ur actually
survived for quite a while, making it through the breakup of Rondina and into the era of
Pangaea, until it broke apart about 208 million years ago into Laurasia and Gondwanaland.
You can now find the remains of Ur in parts of Africa, Australia, India, and Madagascar.
2.7 Billion Years Ago
Kenorland is basically thought to have been made up from multiple smaller cratons
(Zimbabwe, Kaapvaal, Gawler, Pilbara, and Yilgarn) , cratons being stable portions of
continental crust from unstable geologic regions. Picture them as both shields - in
which the basement rock crops out at the surface- and platforms - in which the
basement is overlain by sediment.
At this point in Earth's history, it was pretty much all volcanic/igneous activity all the
time, until those cratons started to collide. When Kenorland started to break up, the
oceans were just beginning to oxygenate and this is the point when the "snowball earth"
theory takes place.
1.8 Billion Years Ago
The formation of Columbia (also known as Nuna and Hudsonland) was the result of
global scale collision events. It consisted of the proto-cratons that had previously made up
Laurentia, Baltica, the Ukranian and Amazonian Shields, Australia and possibly Siberia,
North China and Kalaharia.
When it began to break up, it is thought that its pieces began moving around
independently for several hundred million years and then, about a billion years ago, the
band got back together and formed our next super: Rodinia.
1 Billion Years Ago
Rodinia (along with it's more famous brother, Pangea) is one of the two true "super"
continents. Gaining this title simply because it was massive, and contained many of the land
masses we know today - but all mashed together into one. Unlike Pangea, not as much is
known about Rodinia... its look and feel have been pieced together by comparing similar
geologic features, now widely dispersed.
Interestingly, the extreme cooling of the global climate around 700 million years ago (the
aforementioned "Snowball Earth" theory) and the rapid evolution of primitive life during the
subsequent periods are often thought to have been triggered by the breaking up of Rodinia.
600 Million Years Ago
Also known as the Vendian supercontinent, Pannotia lasted up to the end of the
Precambrian period, about 550 Million years ago. It would eventually split into pieces Laurentia, Siberia and Baltica with the main landmass of Gondwana to the south.
This is when you can really start to see the shapes of today's continents starting to become
recognizable.
300 Million Years Ago
This is the one that everyone has heard of, and because it's the only one we were taught
about in school, is thought of as Earth's only supercontinent. During the Early
Permian, the northwestern coastline of Gondwana smashed into the Euramerican
continent. With the fusion of the Angaran part of Siberia to this combined landmass,
the assembly of Pangea was pretty much done becoming 'super'.
It began to break apart about 200 million years ago, during the Early Jurassic, eventually
forming the modern continents and the Atlantic and Indian Oceans.
200 Million Years Ago
These two guys aren't really a single supercontinent, they are the result of Pangea breaking
in half and creating two enormous continents, Gondwannaland and Laurasia.
Gondwanaland contained most of the landmasses in today's Southern Hemisphere,
including Antarctica, South America, Africa, Madagascar and Australia, as well as the
Arabian Peninsula and the Indian subcontinent, which have now moved entirely into the
Northern Hemisphere.
Laurasia, to the north, contained North America, Europe, and Asia (but not India). Laurasia
is thought to have fragmented into the present continents of North America, Europe, and
Asia some 66 million to 30 million years ago.
The fracturing of both these supercontinents give us the picture of the globe we have today.
250+ Million Years
From Now
Knowing what we know about how plate tectonics work, we can actually theorize what the
continents will be doing down the road. After all, as you read this, the continents are still
moving. It's a fantasy, of course, we still know only a fraction of what we need to
understand about how our planet's plates move and dance and fight with each other.
In the Pangea Ultima scenario, subduction destroys the Atlantic oceanic basin, causing the
Atlantic Ocean to close, bringing the Americas back together with Africa and Europe. As
with most supercontinents, the interior of this massive new continent would probably
become a semi-arid desert prone to temperature extremes.