The ocean floor is famously less explored than the surface of Mars. And when our team of scientists recently mapped the seabed, and ancient sediments beneath, we discovered what looks like an asteroid impact crater.

Intriguingly, the crater, named “Nadir” after the nearby volcano Nadir Seamount, is of the same age as the Chicxulub impact caused by a huge asteroid at the end of the Cretaceous period, around 66 million years ago, which wiped out the dinosaurs and many other species.

The finding, published in Science Advances, raises the question of whether the crater might be related to Chicxulub in some way. If confirmed, it would also be of huge general scientific interest as it would be one of a very small number of known marine asteroid impacts and so give unique new insights into what happens during such a collision.

The crater was identified using “seismic reflection” as part of a wider project to reconstruct the tectonic separation of South America from Africa back in the Cretaceous period. Seismic reflection works in a similar manner to ultrasound data, sending pressure waves through the ocean and its floor and detecting the energy that is reflected back. This data allows geophysicists and geologists to reconstruct the architecture of the rocks and sediments.

Scrolling through this data at the end of 2020, we came across a highly unusual feature. Among the flat, layered sediments of the Guinea Plateau, west of Africa, was what appeared to be a large crater, a little under 10km wide and several hundred metres deep, buried below several hundred metres of sediment.

Many of its features are consistent with an impact origin, including the scale of the crater, the ratio of height to width and the height of the crater rim. The presence of chaotic deposits outside of the crater floor also look like “ejecta” – material expelled from the crater immediately following a collision.

We did consider other possible processes that could have formed such a crater, such as the collapse of a submarine volcano or a pillar (or diapir) of salt below the seabed. An explosive release of gas from below the surface could also be a cause. But none of these possibilities are consistent with the local geology or the geometry of the crater.

Earthquakes, airblast, fireball and tsunamis

After identifying and characterising the crater, we built computer models of an impact event to see if we could replicate the crater and characterise the asteroid and its impact.

The simulation that best fits the crater shape is for an asteroid 400 metres in diameter hitting an ocean that was 800 metres deep. The consequences of an impact in the ocean at such water depths are dramatic. It would result in an 800-metre thick water column, as well as the asteroid and a substantial volume of sediment being instantly vapourised – with a large fireball visible hundreds of kilometres away.

Shock waves from the impact would be equivalent to a magnitude 6.5 or 7 earthquake, which would likely trigger underwater landslides around the region. A train of tsunami waves would form.

The air blast from the explosion would be larger than anything heard on Earth in recorded history. The energy released would be approximately a thousand times larger than that from the recent Tonga eruption. It is also possible that the pressure waves in the atmosphere would further amplify the tsunami waves far away from the crater.

Chicxulub relative?

One of the most intriguing aspects of this crater is that it is the same age as the giant Chicxulub event, give or take one million years, at the boundary between the Cretaceous and Paleogene periods 66 million years ago. Again, if this really is an impact crater, might there be some relationship between them?

We have three ideas as to their possible relationship. The first is that they might have formed from the break-up of a parent asteroid, with the larger fragment resulting in the Chicxulub event and a smaller fragment (the “little sister”) forming the Nadir crater. If so, the damaging effects of the Chicxulub impact could have been added to by the Nadir impact, exacerbating the severity of the mass extinction event.

The break-up event could have formed by an earlier near-collision, when the asteroid or comet passed close enough to Earth to experience gravitational forces strong enough to pull it apart. The actual collision could then have occurred on a subsequent orbit.

Although, this is less likely for a rocky asteroid, this pull-apart is exactly what happened to the Shoemaker-Levy 9 comet that collided with Jupiter back in 1994, where multiple comet fragments collided with the planet over the course of several days.

Another possibility is that Nadir was part of a longer lived “impact cluster”, formed by a collision in the asteroid belt earlier in solar system history. This is known as the “little cousin” hypothesis.

This collision may have sent a shower of asteroids into the inner solar system, which may have collided with the Earth and other inner planets over a more extended time period, perhaps a million years or more. We have a precedent for such an event back in the Ordovician period – over 400 million years ago – when there were numerous impact events in a short period of time.

Finally, of course, this may just be a coincidence. We do expect a collision of a Nadir-sized asteroid every 700,000 years or so. For now, however, we cannot definitively state that the Nadir crater was formed by an asteroid impact until we physically recover samples from the crater floor, and identify minerals that can only be formed by extreme shock pressures. To that end, we have recently submitted a proposal to drill the crater through the International Ocean Discovery Program.

As with the main impact crater hypothesis, we can only test the little sister and little cousin hypotheses by accurately dating the crater using these samples, as well as by looking for other candidate craters of a similar age.

Perhaps more importantly, could such an event happen in the near future? It is unlikely, but the size of the asteroid that we model is very similar to the Bennu asteroid currently in near-Earth orbit. This asteroid is considered to be one of the two most hazardous objects in the solar system, with a one-in-1,750 chance of collision with Earth in the next couple of centuries.

Uisdean Nicholson, Associate Professor of Geoscience, Heriot-Watt University; Sean Gulick, Research Professor of Geoscience, University of Texas at Austin, and Veronica Bray, Research Scientist, Lunar & Planetary Laboratory, University of Arizona

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Before 7:30 p.m., incident command gave orders for resources to work on the incident on Sunday, which included several crews, strike teams and at least one dozer.

Minutes later, the last tankers were being released, with two copters to continue to work the incident until dark.

Also at about 7:30 p.m., the sheriff’s office issued an evacuation warning for the area of Konocti Vista Drive to Anderson Road in the Jago Bay area, located in KEL-E146-B pm Zonehaven. Residents of the area are asked to maintain situational awareness and prepare to evacuate if necessary.

Shortly before 8:15 p.m., the sheriff’s office said the evacuation warning for the area west of Anderson Road was lifted.

However, all evacuation orders east of Anderson Road at Pt. Lakeview remained in effect at that time.

PFAS chemicals seemed like a good idea at first. As Teflon, they made pots easier to clean starting in the 1940s. They made jackets waterproof and carpets stain-resistant. Food wrappers, firefighting foam, even makeup seemed better with perfluoroalkyl and polyfluoroalkyl substances.

Then tests started detecting PFAS in people’s blood.

Today, PFAS are pervasive in soil, dust and drinking water around the world. Studies suggest they’re in 98% of Americans’ bodies, where they’ve been associated with health problems including thyroid disease, liver damage and kidney and testicular cancer. There are now over 9,000 types of PFAS. They’re often referred to as “forever chemicals” because the same properties that make them so useful also ensure they don’t break down in nature.

Scientists are working on methods to capture these synthetic chemicals and destroy them, but it isn’t simple.

The latest breakthrough, published Aug. 18, 2022, in the journal Science, shows how one class of PFAS can be broken down into mostly harmless components using sodium hydroxide, or lye, an inexpensive compound used in soap. It isn’t an immediate solution to this vast problem, but it offers new insight.

Biochemist A. Daniel Jones and soil scientist Hui Li work on PFAS solutions at the Michigan State University and explained the promising PFAS destruction techniques being tested today.

How do PFAS get from everyday products into water, soil and eventually humans?

There are two main exposure pathways for PFAS to get into humans – drinking water and food consumption.

PFAS can get into soil through land application of biosolids, that is, sludge from wastewater treatment, and can they leach out from landfills. If contaminated biosolids are applied to farm fields as fertilizer, PFAS can get into water and into crops and vegetables.

For example, livestock can consume PFAS through the crops they eat and water they drink. There have been cases reported in Michigan, Maine and New Mexico of elevated levels of PFAS in beef and in dairy cows. How big the potential risk is to humans is still largely unknown.

Scientists in our group at Michigan State University are working on materials added to soil that could prevent plants from taking up PFAS, but it would leave PFAS in the soil.

The problem is that these chemicals are everywhere, and there is no natural process in water or soil that breaks them down. Many consumer products are loaded with PFAS, including makeup, dental floss, guitar strings and ski wax.

How are remediation projects removing PFAS contamination now?

Methods exist for filtering them out of water. The chemicals will stick to activated carbon, for example. But these methods are expensive for large-scale projects, and you still have to get rid of the chemicals.

For example, near a former military base near Sacramento, California, there is a huge activated carbon tank that takes in about 1,500 gallons of contaminated groundwater per minute, filters it and then pumps it underground. That remediation project has cost over $3 million, but it prevents PFAS from moving into drinking water the community uses.

Filtering is just one step. Once PFAS is captured, then you have to dispose of PFAS-loaded activated carbons, and PFAS still moves around. If you bury contaminated materials in a landfill or elsewhere, PFAS will eventually leach out. That’s why finding ways to destroy it are essential.

What are the most promising methods scientists have found for breaking down PFAS?

The most common method of destroying PFAS is incineration, but most PFAS are remarkably resistant to being burned. That’s why they’re in firefighting foams.

PFAS have multiple fluorine atoms attached to a carbon atom, and the bond between carbon and fluorine is one of the strongest. Normally to burn something, you have to break the bond, but fluorine resists breaking off from carbon. Most PFAS will break down completely at incineration temperatures around 1,500 degrees Celsius (2,730 degrees Fahrenheit), but it’s energy intensive and suitable incinerators are scarce.

There are several other experimental techniques that are promising but haven’t been scaled up to treat large amounts of the chemicals.

A group at Battelle has developed supercritical water oxidation to destroy PFAS. High temperatures and pressures change the state of water, accelerating chemistry in a way that can destroy hazardous substances. However, scaling up remains a challenge.

Others are working with plasma reactors, which use water, electricity and argon gas to break down PFAS. They’re fast, but also not easy to scale up.

The method described in the new paper, led by scientists at Northwestern, is promising for what they’ve learned about how to break up PFAS. It won’t scale up to industrial treatment, and it uses dimethyl sulfoxide, or DMSO, but these findings will guide future discoveries about what might work.

What are we likely to see in the future?

A lot will depend on what we learn about where humans’ PFAS exposure is primarily coming from.

If the exposure is mostly from drinking water, there are more methods with potential. It’s possible it could eventually be destroyed at the household level with electro-chemical methods, but there are also potential risks that remain to be understood, such as converting common substances such as chloride into more toxic byproducts.

The big challenge of remediation is making sure we don’t make the problem worse by releasing other gases or creating harmful chemicals. Humans have a long history of trying to solve problems and making things worse. Refrigerators are a great example. Freon, a chlorofluorocarbon, was the solution to replace toxic and flammable ammonia in refrigerators, but then it caused stratospheric ozone depletion. It was replaced with hydrofluorocarbons, which now contribute to climate change.

If there’s a lesson to be learned, it’s that we need to think through the full life cycle of products. How long do we really need chemicals to last?

A. Daniel Jones, Professor of Biochemistry, Michigan State University and Hui Li, Professor of Environmental and Soil Chemistry, Michigan State University

This article is republished from The Conversation under a Creative Commons license. Read the original article.