One of the well-known reasons for the extinction of the dinosaurs is that an asteroid with a diameter of about 10 kilometers hit the Earth about 66 million years ago. We usually think that without the asteroid, the dinosaurs probably wouldn't have gone extinct, but is that really the case?
Not necessarily. Because in recent years of research, scientists have found that long before the asteroid hit the earth, the dinosaurs have been hit hard, and because of this, the decline of the dinosaurs, according to this trend, the extinction of the dinosaurs seems to have been arranged in the dark, even without the asteroid, the dinosaurs are likely to go extinct. Let's take a look at what exactly this is all about.
The rocks and strata formed at different times in the history of the earth have their own characteristics, and there are often obvious dividing lines between them, and the "K-Pg boundary" is one of them, this dividing line marks the alternation of the Cretaceous and Paleogene periods, and it has an important feature that the dinosaur fossils we have found are basically below it, and there are almost no dinosaur fossils above it.
The "K-Pg Boundary" was formed about 66 million years ago, and its formation coincided with the time when the asteroid hit Earth. Research in recent years has shown that dinosaur fossils did not disappear all at once at this dividing line.
(↑ "K-Pg Boundary")
Specifically, about 10 million years before the formation of the "K-Pg boundary", the diversity of dinosaurs began to decline rapidly, so that after about 3 million years, the number of dinosaur fossil species has decreased by about 40%, which means that the dinosaurs have been hit hard, so what is the reason for this?
Scientists have found that many of the strata formed during this period have a special phenomenon, that is, at first the seabed features, then coastal features, and finally land features.
Since there are no signs of tilting and bending caused by the "orogenic movement" in these strata, scientists believe that during this period, there was a large-scale "sea retreat" phenomenon on the earth, and the reason for this is probably because the activity of the earth's oceanic crust decreased at that time, so that they slowly settled into the mantle under the action of gravity, which in turn led to the decline of the sea level on the earth.
Therefore, a plausible explanation is that it is the large-scale "sea retreat" phenomenon that caused the rapid decline in dinosaur diversity, because the decline in sea level will cause a dramatic change in the climate on the earth's land.
The most direct effect is that the total precipitation on land will be greatly reduced, resulting in many originally humid areas becoming arid, and the vegetation will also disappear, so that the dinosaurs living in these areas will gradually become extinct due to the loss of habitable environment, in addition to the large areas of arid and barren land will also hinder the dinosaurs from migrating long distances, so that they cannot escape from the natural environment degradation area, which undoubtedly further increases the risk of dinosaur extinction.
But this is not the end of the story, although the decline in dinosaur diversity slowed down to a certain extent after this period, it did not take long for the decline in dinosaur diversity to increase again, especially in the nearly 300,000 years before the formation of the "K-Pg line", the rate of decline in diversity was very fast, which means that the dinosaurs have suffered a major blow.
(↑ The three colors of blue, red, and black in the figure represent the "net value" of new dinosaur species, extinct dinosaur species, and dinosaur diversity as a whole, with a timeline below and a unit of million years)
Scientists believe that the most likely cause is the "Deccan Dark Rock Eruption Event".
The event was a series of large-scale volcanic activity in modern Earth, India, where the formation of lava formations known as the "Deccan Shield" was directly observed in an area of about 512,000 square kilometers and more than 2,000 meters thick, with an initial area estimated by scientists to be about 1.5 million square kilometers, taking into account erosion and continental drift.
Scientists speculate that the dust and gas emitted by this series of large-scale volcanic activities caused huge fluctuations in the Earth's climate at that time, which further deteriorated the living environment of the dinosaurs.
Because until the time point when the "K-Pg boundary" was formed, the trend of decreasing dinosaur diversity has not slowed down, so a reasonable speculation is that the asteroid 66 million years ago is equivalent to pressing the "acceleration button" for the extinction process of dinosaurs, and if there is no asteroid, it is difficult for dinosaurs to escape the fate of extinction according to the trend of decreasing dinosaur diversity.
Of course, this can only be said to be a speculation, so everyone can just take it and don't take it too seriously. It is worth mentioning that after years of research, the scientific community now generally believes that the existing birds on the earth are actually evolved from a theropod dinosaur, so in this regard, the dinosaurs are not completely extinct, but only "non-avian dinosaurs" that are extinct.
(↑ A "descendant of a dinosaur" passes by)