Radiolarian: Heroes are not considered in terms of size

A wide variety of radiolarian worms

uux.cn According to China Science Daily (lead author: Zhang Wenjing): In the vast and endless ocean, there lives an animal that looks insignificant. They are small, less than the size of a grain of millet, but they have a long history of life that they are proud of, and have evolved since the emergence of the Cambrian Period. They are numerous and widely distributed, and the soft mud formed by the sedimentary seafloor after death occupies about 3% of the area of the modern seafloor. These little things are radiolarians. Nowadays, scientists' research on fossil specimens of radiolariae has played an important role in solving problems such as stratigraphic determination and plate movement.

Strange looking

The name radiolarians is related to their unique "appearance". Radiolaria is a single-celled protozoa floating in the ocean. Most of them have a central bone, which is spherical, bell-shaped and other shapes, and the central bone has spines that stretch radially outward, hence the name.

Radiolaria belong to the protozoa Phylum Carnithopodidae. Like other siblings in this extended family, individuals of radiolariae are made up of only one cell. But this single cell is a complete organism with the main life functions expected of being an individual animal. The parts of the cell differentiate, each controlling a certain function, forming an "organoid". For example, they tend to have flagella, cilia, or pseudopods as motility organs.

Individual protozoa are small but very widely distributed, as are radiolaria. The body diameter of radiolaria is generally 0.1 to 0.2 mm, and some can grow up to 2.5 mm. There is also a type of radiolaria that is gregarious, and many individuals are connected together and can reach more than 15 mm in general.

The radial insect's petite body has caused some trouble for its fossil specimen collection and research. Luo Hui, a researcher at the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences, told the China Science News reporter that when collecting fossils in the wild, they could not directly see radiolarians, and even if they held a magnifying glass, they could only glimpse the shadows of some well-preserved radiolarians in the rocks. They need to transport rocks that may contain radiolarian fossils back to the laboratory, undergo special treatment to separate the fossils from the stones, and then use electron microscopes to enlarge them to hundreds or thousands of times to take pictures, using photos for observation and research.

"Of course, the study of radiolarian fossils also has its own unique advantages, that is, they did not become extinct with a long history." Luo Hui said that there are more than 2,000 known fossils of radiolarian worms, and there are about 6,000 species of radiolarian worms that have emerged. We can use the research method of modern and ancient times to infer the living conditions of ancient radiolarians based on the survival and ecological distribution of living radiolarians.

Luo Hui said that in Japan, there are radiolaria experts who specialize in the cultivation of radiolaria, or collect live radiolarians in the ocean and place them under a microscope to observe their behavior. "We can see through the video that most of the radiolaria are preyed upon. They will stick out their pseudo-feet, grab some small pieces of food, and eat it. Some radiolaria have symbiotic algae, which produce nutrients through photosynthesis and can be absorbed by radiolariae. These behaviors are very interesting and are a hot topic in current international radiolariasis research. "In the past, we studied fossils a lot, but now many radiolarians have turned around to study the behavior of living radiolarians." ”

Sedimentation of the deep sea

Radiolarians are widely distributed, from the equator to the polar regions, and in almost all parts of the world. Among them, radiolaria near the equator are particularly abundant and diverse. If you fill the sea with a normal bathtub, the number of radiolarian worms living in it can reach 40,000. Because its shell is siliceous, radiolarians are not easily dissolved after death and sink to the bottom of the sea, but are enriched in large quantities. Their bulk density is staggering, and in a matchbox-sized place, the number of individuals containing radiolaria in the sediment can exceed 120,000. These radiolarian shells piled up on the seabed form a soft mud of radiolaria. "Statistics say that this soft mud covers 3.4% of the entire earth's seafloor area." Luo Hui said.

It is precisely because of the nature of radiolarians that they can deposit the seafloor that they have been able to play a key role in the study of suture zones in the crust plates. "We know that several large plates on Earth will die during the collision process, and the collision belt formed after the demise is called the suture belt. In the suture zone, there are many deep-sea sediments, and among these sediments are only radiolarians and no other fossils. Therefore, radiolarian fossils can serve as key evidence in plate movement. Luo Hui explained.

In recent years, Luo Hui has devoted his main energy to the fossil radiolarian worms in the Suture Zone of the Brahmaputra River in Tibet, and is conducting research related to this. Every summer, Luo Hui takes his research team to the Qinghai-Tibet Plateau to collect fossils. Finding these tiny fossils on the Mangy Plateau is not easy, and in addition to dealing with altitude sickness, it also has to face a fragmented formation.

"The formation of the suture zone is different from the usual formation, it is not continuous, because its tectonic movement is very strong, the original normal upper and lower structure is completely disrupted, so collecting fossils on the plateau is much more difficult than field observation in other places, and the research method will be different." We need to do the opposite, first find out the fossils, and then infer the original stratigraphic order. Luo Hui said.

Paleontologists often have to rely on a bit of luck to find fossils. On the plateau, the factor of luck is obviously heavier.

What impressed Luo Hui the most was that many years ago, one of his disciples found some Paleogene radiolarians in Jiangzi County and published a paper on it, which attracted a lot of attention. After the paper was published, many people went to look for similar fossils, but because the local strata were too chaotic, they could not find them. Some people wonder if this fossil really exists here. In order to confirm this incident, for the next ten years, Luo Hui went to the vicinity of the Qinghai-Tibet Plateau every year whenever he had the opportunity to look for it, and returned empty-handed. The project was over, and he was almost discouraged. In the last year, Luo Hui thought about going to see it casually, so he went to a nearby hill to look for it. At that time, there were several fossils that looked very good, and Luo Hui collected them back. When he came back to look, he found that "the crowd was looking for him for a thousand hundred degrees, but the man was in the middle of the light", which was exactly the radiolarian fossil he had been looking for for many years.

Paleontological research is often accompanied by surprises and disappointments. "That's what makes it fascinating." Luo Hui said with a smile.

Study the gradual heating

Research on radiolarian fossils began in Europe and has since developed faster in the United States, but has recently weakened slightly.

At present, the country with the largest number of radiolarian research in the world is Japan. "The formations in Japan are very special, there are almost no other fossils in them, but radiolarians can be found in most places." Luo Hui introduced. The life history of radiolarian worm is very long, from the Cambrian period to the present, different types have developed in different eras, and its skeleton will be preserved in different rocks, the most common of which is siliceous rock.

"Initially, researchers couldn't strip fossils from the rocks, they had to grind the rocks into flakes and then look at them through a microscope. Of course, the accuracy of this observation is not high, so many of the genera and species that were determined at that time are now considered incorrect and have basically changed. It wasn't until the 1970s that researchers found a new way to process radioleptic fossils and extract them from siliceous rocks. This has greatly promoted the study of radiolarian fossils. "Now, most of our research methods are improved based on this technology to obtain radiolarian entities." Later, researchers found radiolarian fossils in some formations that had not found fossils in the past, which is critical to solving the age problems of that formation. ”

In recent years, due to the hot study of tectonic plates, the academic community has also attached great importance to the study of radiolariasis. "In recent years, the number of radiolarian researchers in China has also increased, and researchers from the Institute of Ancient History, the Institute of The South China Sea, the China University of Geosciences (Wuhan), Tongji University and other researchers are conducting research in different aspects." In 2009, as the president of the International Association of Radiolarian Paleontologists, Luo Hui organized a conference in Nanjing, and basically invited all radiolarian research experts in China to gather together to communicate with international experts. "At least in terms of the number of participants, our country is only ranked after Japan. Nowadays, with the increasing emphasis on basic research in China, more and more students are committed to the study of radiolariasis, which is a good phenomenon. Luo Hui said.

In the future, their research on radiolaria may bring us more surprises.

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