Something strange happened to the planet 467 million years back. It was the end of the era of conodonts, brachiopods and trilobites that thrived in Earth’s oceans. This was replaced by an explosion in invertebrate marine life, closer to what we see today in our oceans.
This phenomenon is called the Ordovician radiation and it is the largest known increase in biodiversity in Earth's past history. Scientists have concluded that this was caused by Earth's cooling climate, which led to an ice age.
What caused the cooling? It's still a controversial question, but new research suggests that we can eliminate one possible explanation, which may be somewhat controversial: Space dust.
According to a 2019 paper this dust was formed by the collision of two asteroids within the asteroid belt between Mars, Jupiter. According to the paper, the dust that spread through the Solar System could have blocked enough sunlight from reaching Earth, triggering a cooling event.
Jan Audun Rasmussen, a geologist from Museum Mors in Denmark, and his colleagues have just published a paper. They conclude that the Ordovician radiation began before the collision of asteroid.
"Our results show that the period of colder and more biodiversity occurred well before the asteroid blast and subsequent meteor bombardment – 600,000 years earlier to be exact," Nicolas Thibault, a geologist and paleontologist at the University of Copenhagen, Denmark.
"This shows that they cannot be connected."
The research team looked to the bottom to answer this question. The research team carefully examined fossils found in the Norwegian sedimentary seabed at Steinsodden, which were preserved in limestone layers. They wanted to date and track changes in biodiversity in the ocean's oceans during the Ordovician period.
They were able to reconstruct the sequence of events that led up to the Ordovician radiation.
Christian Mac Orum Rasmussen, a paleontologist at the University of Copenhagen, stated that "our study shows that a shift toward a colder climate started exactly 469.2 millions years ago." "Two hundred thousand more years later, the temperatures were lower and caused ice formation at the South Pole at that time."
The layers show that the shift towards cooler temperatures coincided in part with an increase in Earth's orbital eccentricity, and axial tilt relative to the Sun. This phenomenon is well-known and occurs regularly. Each shift occurs over thousands of years, creating interglacial and glacial climate cycles known as Milankovitch cycles. These cycles are not related to the current rate climate change.
However, this doesn't mean that asteroid dust did not have an impact on Earth. It was a huge kaboom and its effects still continue today. About a third of all meteorites that fall to Earth today are made up of chunks of it. Researchers said that the effect was not the same as what was found in the original paper.
Jan Audun Rasmussen stated that the cosmic dust created by the asteroid's impact probably prevented biodiversity from increasing. "The dust blocked sunlight which in turn affected most photosynthetic and living processes of animals.
Researchers said that more research is needed to resolve the roles of Milankovitch and glaciation in the Ordovician radiation. However, ruling out cosmic dust was a significant step forward.
Thibault stated that "our study has brought us closer to understanding why this large increase was biodiversity."
"At the exact same time, we also found an important piece to the puzzle regarding how climate affects biodiversity and the life of all living things on Earth. This information will help us prevent future loss of plant and animal diversity.
Nature Communications published the research.
