New dates show massive volcanic eruptions overlap with death of dinosaurs

Modeling what happened after a huge asteroid struck the Yucatan painted a landscape of hell capable of causing massive extinction: stifling dust, huge tsunamis, and enough debris leaving the world. atmosphere to trigger global fires. But questions remain as to whether the impact alone has led the dinosaurs to extinction or whether it has simply completed the work begun by a massive volcanic explosion in India.

The deccan traps cover an area of ​​about half a million square kilometers and the eruptions that created them involved more than one million cubic kilometers of rock. Huge eruptions like this have been attributed to massive extinctions in the past, as they dump a large amount of toxic chemicals into the atmosphere and cause a rapid switch to cooling and warming. And the deccan traps are no exception: people have claimed that they were already killing the dinosaurs or that they had stressed ecosystems so as to pave the way for mass extinction. But not everyone agrees with this idea, and some have suggested that the collision between asteroids had actually resulted in changes in the Deccan Traps eruptions.

Sorting all this requires a better idea of ​​the timing of the eruptions compared to when the impact and the extinctions occurred. In today's issue of Sciencetwo documents are trying to reduce the schedule. Unfortunately, their results do not quite agree.

What and when?

Both documents are based on radiometric dating, but they use different types, each with its own limitations. One of them examines the disintegration of uranium trapped in the zircons that form during volcanic activity. The strength of this method is that it is very accurate. Its disadvantage is that zircons form at high temperatures, which means that they are underground before the eruptions rather than during the eruption itself. So, they do not provide a specific date of the eruption.

To solve this problem, an Indo-Swiss-American team examined huge amounts of zircons and linked their dates to their specific location in the series of eruptions that built the Deccan traps. A statistical analysis then identified all the outliers – a younger zircon under an older layer, for example – and took them into account in constructing a model of the most likely ages of the different eruptions.

This suggests that Deccan traps were built in pulses, with a major eruption occurring about 100,000 years before the impact of the asteroid. An even bigger one happened almost immediately after.

A second team, from India, the United Kingdom and the United States, met with women. The gas starts to get trapped only once the rock has solidified. It therefore triggers the stopwatch during the eruption. The problem is that gas can sometimes escape from the rock slowly over time, which poses fewer problems with zircons.

Overall, this group finds a big picture that overlaps with that of the zircon dating group. But there are differences in the details, and some of them are significant. For example, researchers also found that Deccan Trap eruptions overlapped mass extinction, occurring both before and after the event. But they see no trace of legumes; instead, they see almost continuous eruptions. Most of these materials (about 75%), however, would have been put in place after mass extinction.

The dates of the researchers are also consistent with a major change in the properties of erupting rock occurring at the same time as the impact. This reinforces the idea that the seismic effects of the impact have affected the entire planet.

Eruptions like this release massive quantities of sulfur and carbon dioxide. These have opposite effects. Sulfur forms aerosols that reflect a huge amount of sun, causing cooling. This cooling, however, is short term because aerosols do not have a long life in the atmosphere. Carbon dioxide does, and it produces a subsequent warming through the greenhouse effect. This climate change is thought to have contributed to massive extinctions.

The second paper includes an analysis that correlates eruptions with the signs of climate change, but finds that they do not align well. The authors conclude that the climate has changed, that gas releases do not always match the volume of lava that has broken out. This result raises questions about the impact of Deccan eruptions on ecological disturbances.

Overall, it seems like we have a lot more information, but that does not necessarily lead to a clearer picture. The results confirm that significant eruptions occurred before mass extinction, but the largest of them seemed to occur after, and the effect of eruptions on distant ecosystems was not observed. not clear. And we do not know if the eruptions were a small series of huge explosions or a relatively steady pace of smaller activities.

The good news is that if you are a fan of dinosaurs and want to know how they are doing, there is still science to be done.

Science, 2019. DOI: 10.1126 / science.aau2422, 10.1126 / science.aav1446 (About the DOIs).