Ocean microbes helped sustain life after asteroid impact wiped out dinosaurs, finds study

Life on Earth: When dinosaurs were wiped off the face of the Earth by an asteroid collision 66 million years ago, it was the ocean microbes that flourished due to the impact, a new study has found. Researchers have found evidence in microscopic crystals of rock that suggests that the world’s oceans had been covered by massive algae and photosynthetic bacteria blooms. These microbes became the food source for the larger species of sea creatures, essentially sustaining life, at least in the water bodies covering the Earth.

Back in 2016, some researchers had drilled in the Chicxulub crater in the Gulf of Mexico. The crater is buried under the sea floor and had been caused by the impact of the asteroid. Scientists had found that the sediments deposited there just after the impact were rich in calcium carbonate mineral called micrite. Calcium carbonate, commonly found in limestone, precipitates in the oceans. Plankton and corals build skeletons of calcium carbonate, while microbes like bacteria produce it. Moreover, it can form directly from seawater as well.

This new discovery was led by Timothy Bralower, a Professor at Penn State University, who had also spotted micrite in rocks from western Pacific Ocean back in 2001. The micrite that he and his team had then identified also dated back to the time of the collision. Bralower said that when the team now saw the micrite layer in the crater, they realised that they had seen it before and it was a ‘bingo’ moment for them.

When he then looked at his extensive collection of rock samples, he realised that rocks from as many as 31 sites worldwide contained a micrite layer that was 66 million years old. He said that they saw it all over the oceans.

To understand the formation of the micrite, the team used electron microscopes to look at the minerals closely. The researchers found that often, the crystals had been composed of microcrystals that were shaped like scalenohedra having more than eight sides, or six-sided rhombohedra. The researchers also realised that previous teams had not seen these structures because they had not been looking as closely, without enough magnification.

In the research published in Earth and Planetary Science Letters, accessed by Financial Express Online, the team said that the microcrystals they observed were highly similar to the calcium carbonate that modern-day bacteria produce, and hence, they reached the conclusion that most of the micrite they observed were likely to be biological in origin. The researchers have suggested that the life responsible for the creation of this micrite was probably part of a “survival microbial community” emerging from the collision.

Researchers have also shown that apart from wiping out much of the life on land, the collision had also decimated the ecosystems in the oceans. They showed that vaporized rock had led to a building up of sulfuric acid, which contained toxic metals like lead and mercury and rained on the oceans. As a result, over 90% of marine phytoplankton became extinct.

Biogeochemist at University of Colorado Julio Sepulveda, who was not a part of the research team, said that still, it was this destruction that cleared the way for newcomers.

Bralower said that these newcomers were algae and photosynthetic bacteria that were ready to take over the Earth. As they bloomed across oceans, they would probably have served as a food source, with animals like krill and shrimp feeding on them, the research team proposed, adding that the evidence of their existence was left behind as micrite.

Bralower and his team further suggested looking even before the asteroid collision to see if similar blooms can be found after other mass extinctions. Bralower said that if researchers would start probing around the Permian extinction, which took place 252 million years ago and led to the extinction of 90% of the species, there was a chance that similar structures would be found there as well.