500 million years ago, the evolution of life on Earth entered a period of prosperity, and within a few million years, the once empty oceans were suddenly filled with many new life forms, and many creatures appeared on the stage of the Earth's oceans. This was the first species explosion revealed in the fossil record, the Cambrian Species Explosion.
But scientists have now discovered that the Cambrian explosion, while spectacular, stopped shortly after it began. So, what is the force that drives life on Earth to continue to evolve?
In recent years, there has been a little-known event in the history of earth's biological evolution - the "Ordovician species explosion" (also known as the "second species explosion")
It has aroused great interest from the scientific community. Paleontologists assert that this event is no less significant to the evolution of Earth's organisms than the "Cambrian species explosion."
The end of the crossbow of the first great explosion of species
In the early Cambrian period, life on Earth evolved into its first period of prosperity, but by the middle and late Cambrian period, the Earth became empty and lonely.
The Cambrian Period, which began 542 million years ago and ended 510 million years ago, has been a period of great interest to paleontologists. For tens of millions of years before that, the most complex life forms on Earth were nothing more than a few marine microbial communities that formed stromatolites. Stromatolites are the oldest and most primitive microbial ecosystems on Earth, with the oldest stromatolites dating back to early Archaic archeoptery 3.5 billion years ago. Later, the stromatolites were replaced by the enigmatic and unfathomable "Ediacaran Fauna" of the first larger life forms on Earth. The "Ediacaran Fauna" is the oldest post-mezoic fauna of the Late Precambrian period (600 to 700 million years ago). Nearly 20 million years later, by the beginning of the Cambrian period, the various animals we see today began to appear.
During this period, trilobites and other arthropods began to occupy the ocean and became the hegemon of the ocean.
The marine microorganisms of stromatolite became their food and gradually declined. The abundance of nutrients in the ocean nourishes many filter-eating animals, such as sponges, mollusks, echinoderms, and brachiopods that are very similar to clams. In addition, a variety of biological reefs (the coopers became extinct in the Jurassic) around some of the marine benthic creatures called "Paleo cups".
Unfortunately, such a "garden of Eden in the water" did not last long. The fossil record suggests that by the middle Cambrian, biodiversity began to decline. Some scientists once believed that about 515 million years ago, a mass extinction of species began on Earth, and the number and variety of species were greatly reduced. However, later studies have shown that the decline in biodiversity during this period is not the result of a mass extinction, but due to a sharp decline in the rate of emergence of new species, only 1/5 to 1/3 of the original, far lower than the rate of species extinction. As for why this is happening, it is not clear.
Whatever the reason, due to the great decline in biodiversity, by 510 million years ago, animal species had dropped from about 600 at its peak to 450. Scientists describe the earth as very empty and lonely during the mid-to-late Cambrian period, and the number of species is surprisingly small. The Cambrian species explosion was like a damp firecracker, and suddenly fell silent.
In just a few million years after the cambrian began, a large number of multicellular organisms, including almost all the ancestors of the living animals, suddenly appeared, an explosive biological evolutionary event known as the "Cambrian species explosion". Shelled, skeletal marine invertebrates tended to flourish, living benthic, feeding on tiny seaweed and organic matter particles, the most prosperous of which were arthropod trilobites (hence the Cambrian period also known as the "trilobite era"), followed by brachiopods, paleococcus, echinoderms, and gastropod leafpods.
Gill shrimp worm large double-petaled shell arthropods. Double-petaled shell arthropods are diverse, ranging from 1 mm to 100 mm or more for large, and many species have perfectly preserved soft appendages. Studies have confirmed that similar shell lobes are wrapped in very different soft bodies and appendages, so their shell flaps cannot be used as a basis for classification and interrelationship, and the shell is the result of convergent evolution.
Sea lilies belong to echinoderms, the body is divided into stems (including roots and stalks), calyxes, wrists three parts, most of them live on the seabed with stems fixed, looking far away, like the beautiful lilies in plants, hence the name.
There are still more than 700 species that survive in the modern ocean.
Grotesque worms belong to the leaf-footed animals, with a large head and a dorsal side of the trunk with 7 pairs of strong long spines that grow diagonally upwards, like "worms with long legs".
Pika worms have distinct and regular knots on their bodies , looking a lot like cephalopods , and may be more like eels when swimming. There is a very primitive prokaryodondon, probably the earliest ancestor of today's vertebrates.
The Pika worm is only 5 cm long on average and can swim out of the water with its body and broad-caudal fins.
The head of the Nek shrimp looks like a snake, but the body resembles a fish. It seems to be a combination of two creatures.
Odd shrimp belong to the leafypods. With a body length of more than 2 meters, it was the largest and fiercest predator in the ocean at that time.
The odd shrimp has a pair of giant eyes with a handle, a pair of segmented giant forelimbs for quick prey, a beautiful large tail fan and a pair of long tail forks. Odd shrimp are not good at walking, but can swim fast.
Oil ctenophores
It belongs to the primitive trilobites. The tail is small , with large head and eyes , and has numerous thoracic segments with shell needles , one of which is more conspicuous than the others. The thorax is tapered and becomes smaller and smaller. Around the cephalic nails is a narrow circle of crystals that form a joint with the buccal shell needle. The protective film of the exoskeleton is very thin.
Soft tongue snail
The shell is usually large, broadly tapered, with a distinct distinction between the dorsal and ventral shells, often with a mid-groove or mid-ridge.
Brachiopods have two shells, equal or unequal in size, covering both sides of the dorsal abdomen. The difference between brachiopods and bivalves is mainly that the former is that the dorsal and ventral shells are symmetrical along the longitudinal midline, the two shells themselves are asymmetrical, and the latter is symmetrical in terms of the two shells themselves.
A spectacular sight of the Ordovician species explosion
At the beginning of the Ordovician, life on Earth re-accelerated like a spark, and some unprecedented creatures began to appear on Earth.
By 510 million years ago, at the beginning of the Ordovician, life on Earth had re-accelerated its evolution like a spark. First, some seaweeds began to multiply in large quantities, providing a lot of food for filter-feeding organisms, stromatolite organisms were once again expelled from the stage of life evolution, sponges became the main builders of coral reefs, and corals joined them. The ocean is back to life.
The evolution of life on Earth began to speed up again, and some unprecedented creatures began to appear on Earth. Although the large new species of large biota that emerged during the Ordovician period were only mosses,
But the original species increased dramatically in both species and numbers, and their prosperity soon surpassed that of the Cambrian Period. If there was a vivid picture of a dizzying array of biological diversity during the Cambrian period, it was not until the early and mid-Ordovician periods that the degree of biological diversity was truly breathtaking.
At the end of the Ordovician period, biodiversity not only reached unprecedented levels, but was never surpassed in the next 200 million years. Along today's coastline, fossils of organisms that first appeared in the Ordovician period, such as starfish, sea urchins, oysters and scallops, can be found. The ecology of the Ordovician period was also more complex than ever. During the Cambrian period, the field of activity of organisms was mainly limited to water, although there may be a few worms in the mud probing their heads, and some strange creatures appeared on the land on the shore, but at that time, the activity stage of earth creatures was mainly in the water. During the Ordovician period, with the emergence of "newcomers", more and more creatures lived in a particular habitat, and some creatures had to explore a different way of survival than usual. Some cave creatures tumbled under the seabed, drilling deeper and deeper, developing new habitats. Digging holes in the seabed is a good survival strategy, and living on layers of piles of seafloor sediment is also a good way to survive.
As competition becomes more and more fierce, organisms have to become more and more "smart" to survive, such as filter-eating animals, which used to passively wait for food that drifts with the current to "reach their mouths", but now they have to actively filter seawater to absorb nutrients.
There is also a way to survive, and that is to escape this highly competitive seabed altogether. By the middle of the Ordovician, several larvae of different biota had evolved the ability to swim away from the ocean floor, perhaps to avoid the swaying tentacles of filter-eating organisms. At this point, life began to move toward land: some simple plants grew up in the wetlands, and some aquatic arthropods that looked a bit like scorpions, the plate-footed horseshoe crabs, took a tentative first step along the coastline toward land.
This vibrant and prosperous scene is unprecedented in the history of the earth. To the surprise of scientists, the Ordovicians were the only period in the evolutionary history of life on Earth that flourished without relying on mass extinctions to make room for new species to emerge. Why? It's still a mystery.