Let’s dig some history first !.
If we closely observe our globe we can see that the total land area is actually an amalgamation of the 7 continents. This made Alfered Wegner (1912) propose the concept of Pangaea (single supercontinent) called Wegener’s drift theory. He postulated that Pangaea fragmented late in the Triassic period (approx 250 million years ago) and the parts then began to move away from one another and became what we see now the 7 continents. But his hypothesis lacked the explanation on how the continents are drifting across the earth’s surface. Later he came up with different ideas to support his hypothesis like explaining about the forces, orogenesis etc. but because of the prevailing belief of that time ie, the earth was solid and immovable made scientific community dismiss Wegener’s theories. At this time(1929) itself another man Arthur Holmes elaborated Wegener’s hypothesis and came up with the idea ‘ Mantle undergo thermal convection’, Holmes idea also didn’t receive any attention till the 1960s. With the advancement of science and discoveries, after a long 30 years made Harry Hess(1962) and R.Deitz(1961) to publish a hypothesis known as ‘seafloor spreading’ which was similar to that of Holmes and which was more convincing to the scientific community. From then the advancement in this area rose exponentially. The current theories explaining the mechanism of continental drifts go to THE PLATE TECTONICS.
The theory of plate tectonics:
1. The earth surface is covered by a number of crustal plates.
2. The ocean floor are continuously moving, spreading from the centre, sinking at the edges, and being regenerated.
3. Convection currents beneath the plates move the crustal plates in different directions.
4. The source of heat driving the convection current is radioactivity deep in the Earth’s mantle.
What is the importance of plate tectonics?
We all know about Earthquakes and volcanic eruption. These are related to tectonic activities. But there are more to plate tectonics. Recent studies found that Understanding plate tectonics will be the major key to understand our planet and it’s habitability. Some researchers even believe that without the movement of the continents life would not have evolved into complex forms as we see now.
We have already learned so much about our planet by studying the history of the Earth’s magnetic field. A more detailed record of Earth’s magnetic past will provide answers regarding the formation of continents as well as the behaviour of our magnetic field ie through Paleomagnetism.
((The study of magnetic rocks and sediments to record the history of the magnetic field. Some rocks and sediments contain minerals which respond to the magnetic field. When rocks form, the mineral aligns with the magnetic field preserving its position. These magnetic signatures help paleomagnetists to date the rocks and map the position of the field at the time of their formation.))
And most importantly about the origin and life.
Now we have got some interesting news!
Let’s begin with this video
Okay, now we know about the earth’s crust. The scientific community believed in Crust Singularity like Alfred’s Pangaea. Only before some 4 billion years ago these crusts started fragmenting and then began crashing into each other forming the plate tectonics. But we know only little about this transition, how and when this transition took place since the plate tectonics continuously recycle the earth’s rocks, melting crust, sprouting volcanic eruptions.. washing away the evidence of the distant past.
“Basically the first half of Earth’s history is represented today by only about 5% of surface rocks,” says Brenner, a PhD student, University of Harvard.
But our scientific society was not ready to give up on their search for the past and there began the hunt. In summer 2017 Brenner and Roger Fu ( Harvard’s paleomagnetist ) started their trip to Australia. The Pilbara craton in Western Australia is one of the oldest slices of ancient Earth’s crust stretching about 500 km was formed early as 3.5 billion years ago. They drilled into a portion of this craton known as the Honeyeater Basalt. They noted the position and orientation for each and combined them with the previously collected samples and analyze the magnetic signature. On further testing confirmed that they represented true ancient magnetic signatures of the rocks. The team then compared the calculated position of honeyeater basalt to a previously outcrop of rock nearby which was slightly older and contain an earlier magnetic signature. The analysis was that the crust was shifting about 2.5 cm every year at the time these rocks formed.
Alex Brenner says ” It is comparable to the speeds of plate motion that we can see happening on the modern Earth.” This finding hints us that just over a billion years after our planet formed, plate tectonics could have already been reviving up. But still, we don’t know the mechanism driving this early movement and we need more pieces of evidence to confirm this.
But if it was indeed the beginning of plate tectonics then it is pointing to the astounding early start of earth’s geological churn, which was a pivotal point for the evolution of life as we know it.
At last “By understanding the origin of plate tectonics you can try to nail down the timing of events that were crucial for the development of life on this planet ” — geochemist Val Finlayson.
-Bincy Babu Raj
Credits- National Geographic
Author
