The rushing mountains and lakes, as well as the erosion caused by the rainy season, these natural water streams will carry some solid particles on the surface of the earth and a large amount of sediment, and eventually they will flow into the sea.
So how much sediment flows into the sea every year?
In this regard, scientists have speculated on the amount of sediment carried by large and small rivers, according to the state of sediment transport, the world's turbidity of the river carries about 13.5 billion tons of sediment (the Yellow River on the mainland has 1.2 billion tons of sediment flowing into the sea every year), plus the riverbed and flood transported sediment in the range of 1 billion to 2 billion tons.
As a result, the amount of sediment flowing into the sea around the world each year can be estimated at around 15 billion tonnes. The Earth has been around for 4.6 billion years, and you can imagine the staggering amount of sediment flowing into the ocean floor.
Such a huge amount of sediment flows into the seabed but quietly, where did it go?
This question must begin with the relationship between the continent and the sea. In 1912, the German meteorologist and geologist Wegener found that the coastline on both sides of the Atlantic Ocean coincided very well when looking at the map, so he collected geological, biological, meteorological and other aspects of the data and came to a surprising conclusion.
That is, a long time ago, the Earth was a supercontinent, and this continent later split to form a new continent, which later drifted to form the continent we see today, which is the "continental drift theory".
The discovery of the theory of continental drift is staggering, and scientists have begun to study what is the dynamic that causes the continent to drift.
In 1872, scientists used the bathymetric hammer to discover a huge raised mountain range in the middle of the Atlantic. Then, in mid-1925 and 1927, the scientists of the German Meteor re-tested the existence of this mountain range during the expedition, which is the "Mid-Atlantic Ridge" that will reach Antarctica all the way south from the Arctic Ocean.
This submarine mountain range stretches in an S-shaped shape from north to south, with a total length of 75,000 kilometers, which divides the earth in two and is also the longest mountain range on earth. Scientists have also found that the rock layers around the submarine mountains are much younger than the land rocks, the sediments on the seafloor are thin, and there are few volcanoes. This shows that unlike the long history of the ocean, the seabed is very young.
In the following decades, scientists discovered the mid-Indian And Pacific ridges. With the constant updating of exploration techniques, in the 1950s, it was determined that the seafloor of every ocean had mountain ranges that made up a vast system of submarine mountain ranges.
The discovery of the mid-ocean ridge led scientists to refocus on Wegener's "continental drift theory", and its discovery made us an important step in the understanding of the Earth, and also gave birth to the later "theory of seabed expansion", which further developed into the theory of plate motion as we know it today.
Around 1960, the American scientist Hesditz proposed the "theory of seabed expansion", which further explained the dynamics of plate movement. The theory of seabed expansion holds that convection of mantle material is the main driver of plate movement. The Earth can be divided into crust, mantle, core from the outside to the core, and there is magma in the mantle close to the crust.
There is thermal convection in the mantle, and the lava material at the top of the mantle forms a high temperature upwelling, rising and gushing out in the middle of the ocean ridge, encountering seawater solidification, forming a new crust, and continuously pushing the original ocean crust outward, so that the entire seabed continues to expand from the mid-ocean ridge to both sides. When the expanding oceanic crust meets the continental crust, the lower oceanic crust will swoop down into the mantle below the continental crust during the impact, forming trenches and coastal mountains.
The ground close to the earth's crust is often called the lithosphere with the earth's crust, and the plate movement will make the lithosphere above slowly move, which is the continental drift movement. Drift between continents has caused them to separate and collide with each other, resulting in mountains and rift valleys, such as the Himalayas and the Great Rift Valley of East Africa. Among them, the Himalayas are located in the southern part of the Qinghai-Tibet Plateau, which is the border between mainland Tibet and India, Nijour, Pakistan and other countries. This natural barrier was formed by the collision of the Indo-Australian Plate with the Eurasian Plate.
According to the measurements, the Indian plate is still moving north at a rate greater than 5 centimeters per year, which makes the Himalayas still rising. Its main peak is Mount Everest, which is now 8844.43 meters above sea level, and the latest measurement data also show that Mount Everest is about 1 cm taller every year. This actual data also confirms that the continents and oceans are constantly moving.
The mantle material gushes out of the mid-ocean ridge, collides with the land and then subducts and sinks, and then melts into the mantle, forming a cycle that achieves a balance of growth between rebirth and demise.
In this process, sediment, as solid particles of sediment, mineral rocks, etc., also melts into the mantle with the movement of the seabed plate, or becomes a new crust, or becomes part of the submarine mountain range, and continues to repeat itself.
Therefore, the sediment that flows into the seabed does not disappear, but joins the plate movement and becomes part of the "metabolism" of the seabed. The discovered undersea mountains have also become the core of the movement of the continents and oceans, allowing everything in nature to circulate.
The theory of seabed expansion is a further form of interpretation of the theory of continental drift and is also an important theoretical pillar of the theory of plate tectonics. Plate tectonics theory integrates geological phenomena such as seabed expansion theory, continental drift, earthquake and volcanic activity into a unified theoretical system, explains the global tectonic movement process and its interrelationship with a unified dynamic model, explains the many phenomena of earth's life activity, and also allows us to have a deeper understanding of the evolution of the earth and the exploitation of natural resources.
Plate tectonics theory is a synthesis of the research results of many disciplines, the establishment of the geotectonic theory, although the current explanation of a variety of continental plate and activity, but the evolution process inside the plate is still a problem, for the age of continental rock layers can be detected more than 3 billion years or even more than 4 billion years.
However, the rock layers on the ocean crust on the seafloor are only 200 million years old, and this complex magmatic activity and metamorphism are difficult to prove in more convincing terms or experiments, for which science is still constantly exploring and studying.
In November 2021, there was new research evidence for plate tectonic theory. The State Key Laboratory of Geological Processes and Mineral Resources, located at The China University of Geosciences in Wuhan, has published the latest scientific research results, extending the large-scale empirical evidence of plate tectonic theory to 2.7 billion years ago. This achievement was discovered by professor Tim, an internationally renowned expert in the field of plate tectonics, and took the orogenic belt in the central part of north China as the research object, providing the most direct evidence for the existence of large-scale horizontal plate tectonics in the early earth (Archean).
The establishment of plate tectonic theory has many scientific bases and measurement data, and its scientific foundation is solid and deep. We also believe that with the continuous upgrading of scientific detection methods, more and broader research areas will be discovered and explored by humans.
Resources:
[1] How was the plate tectonic theory born? Guan Shiqiao. Earth. 2005(06)
[History of the development of geotectonic theory[J]. HE Xiang. Inheritance. 2009(12)
[3] Submarine mountains-mid-ocean ridges[J]. LIANG Xinfeng. Encyclopedia knowledge. 2013(19)
[4] A university research team in Wuhan pushes the large-scale empirical evidence of plate tectonic theory to 2.7 billion years ago, Xinhua Net, 2021-11-04.
Author: Feng Feng Preliminary Review: Xu Moyuan Proofreader: Xiao Wan