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Fossil shark teeth are abundant and can date the past in a unique way

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theconversation.com – Stephanie Killingsworth, Ph.D. Student in Geological Sciences, University of Florida – 2025-02-03 07:31:00

Fossil shark teeth are abundant and can date the past in a unique way

A paleontologist holds a megalodon fossil tooth.
Kristen Grace/FLMNH, CC BY-SA

Stephanie Killingsworth, University of Florida and Bruce J. MacFadden, University of Florida

The ratios of strontium isotopes in fossil shark teeth can be used to better understand how coastal environments evolved in ancient times, according to our newly published work.

As paleontologists with the Florida Museum of Natural History, we’re interested in understanding ancient Florida environments.

Our study was one of the first to date Florida coastal deposits using fossil shark teeth and a technique that looks at variations in ocean strontium. Strontium is a chemical element that occurs naturally in rock, soil and water.

Ocean strontium values change over time, which makes measuring the levels of the chemical element a unique global system for determining the age of similar coastal sedimentary rock deposits worldwide.

Changes in strontium isotope ratios have multiple causes. Land erosion deposits strontium into oceans, while carbonate-producing marine life produce and release strontium when building their skeletons. Strontium is also released by deep-sea vents.

Geochemist Donald DePaolo and geologist B. Lynn Ingram discovered variations in ocean strontium by examining strontium isotopes ratios in marine sediments, including fossils. The levels of strontium isotopes in marine sediments provide a “time stamp” that correlates to the strontium value of the seawater at that time.

That data allowed scientists to map out ratios of strontium isotopes in seawater over time. This global strontium seawater curve correlates to the geologic timescale. Scientists use the curve to reconstruct past ocean chemistry and climate conditions, as well as the age of mollusks and other shell-producing marine fossils.

Why it matters

Properly dating ancient sites is key to understanding how Earth and its living creatures evolved over time.

But historically, strontium dating, while reliable, had limitations.

For example, it works best in fully marine environments and is challenging to use in fossil sites along coastlines. That’s because the strontium values might be influenced by land sediments and freshwater rivers.

Additionally, material used for strontium dating must not have undergone considerable physical and chemical change during fossilization, the preservation of once living things from the past. Any major chemical alteration to the fossil can affect the strontium value and give an inaccurate date.

Our study shows that fossil shark teeth are more resistant to these types of changes due to their outer enamel-like surface.

Remarkably, fossil shark teeth are also incredibly abundant. Sharks ruled the earth’s oceans for 400 million years, and every individual grows and sheds thousands of teeth in their lifetime.

How we did our work

Florida fossil sites are unique in that they possess some of the richest fossil sediments for important times in geologic history. These sites can help us understand changing climates, vegetation and sea levels over time.

The Florida Museum of Natural History has a collection of over 115,000 shark tooth specimens from Florida alone.

To do our study, we selected shark tooth specimens from two significant Neogene-period fossil sites in Florida. The Neogene, from 2.6 to 23.5 million years ago, was a time of immense change in biodiversity because of changing climates.

We analyzed the strontium present in powdered samples collected by shaving a thin layer from the surfaces of the teeth. The age of the teeth helped to clarify the age of the fossil sites where they were collected. This data enabled us to calibrate and differentiate the ages of our two sites, Montbrook and Palmetto Fauna Bone Valley, by about 600,000 years.

Before our study, scientists could estimate the age of the sites based only on mammal fossils. The sites were thought to be the same age. Our work provides a more precise date.

These ages offer new insights into what happened in the southeastern region of North America, some 5 million to 6 million years ago. Our revised age calibrations coincide with global events, including major sea-level fluctuations and the Great American Biotic Interchange – the migration of land mammals between North and South America after the formation of the Isthmus of Panama 4 million to 5 million years ago.

For example, because certain species of ground sloths are not found at the Montbrook site (5.85 million years old) but are found at the Palmetto Fauna Bone Valley site (5.22 million years old), it suggests the immigration of ground sloths into North America occurred between these two dates.

The Research Brief is a short take on interesting academic work.The Conversation

Stephanie Killingsworth, Ph.D. Student in Geological Sciences, University of Florida and Bruce J. MacFadden, Distinguished Professor Emeritus, University of Florida

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The Conversation

The US energy market has its troubles, though it may not be a ‘national emergency’

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theconversation.com – Seth Blumsack, Professor of Energy and Environmental Economics and International Affairs, Penn State – 2025-03-05 13:23:00

This Montana refinery processes crude oil imported from Canada.
AP Photo/Matthew Brown

Seth Blumsack, Penn State

President Donald Trump’s declaration of a “national energy emergency” on his first day in office – and which he reiterated during his address to Congress on March 4, 2025 – might have seemed to echo other national emergencies, like those presidents declared in the wake of the Sept. 11, 2001, terrorist attacks and to deal with the COVID-19 pandemic in 2020.

But there has never before been a national energy emergency. During the energy crises of the 1970s, President Jimmy Carter declared local or regional energy emergencies in a handful of states. These actions suspended some environmental regulations, such as air-pollution limits for coal-fired power plants, for very short periods to make sure those states’ residents had enough electricity.

When a president declares a national emergency, he claims significant powers under the National Emergencies Act, which allow him to take steps to solve the emergency. In this situation, Trump might seek to override environmental regulations, order utility companies to buy power from particular power plants, or invoke the Defense Production Act to secure materials needed for power plant construction.

A flat, smooth area of dirt has trucks parked on it near industrial equipment.
A natural gas well pad in Washington County, Pa., is one of many sites around the nation where fracking has boosted U.S. energy production.
Rebecca Droke/AFP via Getty Images

Six weeks into his presidency, Trump had not taken any action to address this emergency, though during his speech to Congress he said he wants to increase drilling and build a new natural gas pipeline in Alaska. And Trump’s discussion of energy policy has not directly referred to the consumer price hikes expected as a result of the 10% tariffs he imposed on Canadian oil, gas and electricity starting on March 4, 2025.

Critics of the president’s declaration have described it as a “giveaway” to the fossil fuel industry in the form of looser regulations and measures to make it easier to drill for oil on government-owned land. In fact, the executive order’s definition of “energy” excludes energy generated from wind and solar, as well as efforts to conserve energy – all of which were major parts of the Biden administration’s energy strategy.

As someone who has studied energy markets for decades, I have seen several events that might qualify as energy-related emergencies, such as meltdowns at nuclear power plants around the world, shortages of electricity and natural gas, and massive power blackouts.

But over the past 15 years, the United States has become a global energy superpower even without any emergency declarations. The advent of hydraulic fracturing unleashed a wave of oil and gas production, even as U.S. energy demand barely budged. In a time of such energy abundance, there is no clear emergency on the scale of the energy crises of the 1970s. But there are some causes for concern.

Big increases in domestic production

One goal Trump’s declaration sets out is to increase what the executive order calls the nation’s “energy security.” Usually that phrase refers to an ability to operate using energy produced within the U.S. rather than overseas – particularly from countries that have long-standing conflicts or disagreements with the United States.

Based on raw numbers, however, the U.S. is already quite energy secure. In 2023, the nation produced nearly 13 million barrels of oil per day, which is more than any country has ever produced in the history of the oil business. Since 2015, when a federal ban on oil exports was lifted, the U.S. has been increasing the amount of oil it exports every year. And for the past several years, the U.S. has been the world’s leading exporter of gasoline, sending 10% of its total annual production to other countries.

Since the start of the shale-fracking boom in the mid-2000s, U.S. production of natural gas has also been increasing. The country’s natural gas exports have also risen over the past 10 years, though they have been limited by the number of ports that can handle liquefied natural gas cargo.

Still a net importer of oil

The U.S. produces plenty of oil to meet its demands, but not the kinds of oil that American refineries are designed to process into useful fuels.

Therefore, despite the increases in domestic production, the U.S. is still a net importer of crude oil. In 2023, the U.S. imported almost twice as much oil as it exported.

And U.S. refineries’ output of gasoline and heating oil depends on imported oil. Most oil refineries in the U.S. are quite old and were engineered to process so-called “heavy” crude oil produced in countries such as Canada, which is historically the United States’ biggest source of imported oil.

Most of the recent increase in U.S. oil production comes from hydraulic fracturing of shale and is so-called “light” crude oil. Refining light crude would require new refineries or a major reengineering of existing refineries, with new equipment, expanded capacity or both.

Making those changes would be very expensive. So refinery owners are hesitant to make these kinds of investments because there is a risk that the investments won’t pay off. Because U.S. refineries produce so much gasoline and have limited capacity, the U.S. also continues to import some refined petroleum fuels such as jet fuel.

One large ship moves in front of another large ship; both are attended by tugboats.
A liquefied natural gas tanker ship moves toward Cameron Pass near Cameron, La.
Washington Post via Getty Images

A fragile power grid

Concern over the nation’s aging electric power grid is another focus of Trump’s energy emergency declaration. Experts have been issuing warnings for years. A 2024 study on the national transmission grid commissioned by the U.S. Department of Energy has concluded the U.S. needs to double the size of the grid in the next couple of decades.

For the first time in nearly half a century, the U.S. is facing the prospect of rapidly increasing electricity demand. The demand for power has always gone up and down a bit with population and the health of the economy, but this time is different. Growth in electricity demand is now driven by the construction of massive data centers and by electrification of cars and heating and cooling systems. The Department of Energy reports that data center electricity use in particular has tripled in the past 10 years and could easily double in the next few years. At that rate, data centers could account for over 10% of all electricity demand in the country before 2030.

The U.S. supply of power generation in many regions is not ready for this surge in demand. Many power plants – particularly the older ones and those that burn coal – have shut down in the past several years, driven by a combination of economic pressures and environmental regulations. Building new power plants in many parts of the U.S. has become bogged down in regulatory red tape, public opposition and economic uncertainty. The North American Electric Reliability Corp., which develops standards for grid reliability, has placed over half of U.S. states at some level of risk for not having enough power generation to meet anticipated future demand.

Electricity poles and wires stretch above a road.
A study has found that the nation’s electricity grid is expected to need significant investment to handle rising demand.
Paul Bersebach/MediaNews Group/Orange County Register via Getty Images

Will declaring an emergency help?

Under Trump’s energy emergency declaration, the administration seems likely to take actions that will make it easier to drill for more oil and gas. And the federal government may also make it easier to build power plants that run on coal, natural gas and possibly nuclear fuel.

But expanded fracking, in and of itself, will probably not address any energy security issues in the U.S., unless there are major investments in refineries to handle the increased oil production. Reducing the barriers to building power plants addresses a much more pressing problem, but the country would still need to expand the transmission grid itself, which does not get as much attention in the president’s declaration.

Time will tell whether the energy emergency declaration will be used to solve real problems in the nation’s energy supplies, or whether it will be used to further bolster oil and gas producers that have already made the U.S. a global energy powerhouse.The Conversation

Seth Blumsack, Professor of Energy and Environmental Economics and International Affairs, Penn State

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COVID-19 is the latest epidemic to show biomedical breakthroughs aren’t enough to eliminate a disease

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theconversation.com – Powel H. Kazanjian, Professor of Infectious Diseases and of History, University of Michigan – 2025-03-05 07:13:00

COVID-19 has become a part of modern life that many people don’t pay much attention to.
Spencer Platt via Getty Images News

Powel H. Kazanjian, University of Michigan

The COVID-19 pandemic transformed over the past five years from a catastrophic threat that has killed over 7 million people to what most people regard today as a tolerable annoyance that doesn’t require precaution. Nonetheless, COVID-19 continues to kill over 2,000 people per month globally and cause severe illness in the infirm or elderly.

The evolution of the COVID-19 pandemic – from devastation, to optimism for eradication, to persistent, uneven spread of disease – may seem unprecedented. As an infectious disease doctor and medical historian, however, I see similarities to other epidemics, including syphilis, AIDS and tuberculosis.

Vaccines, medications and other biomedical breakthroughs are necessary to eliminate epidemic diseases. But as I explore in my book, “Persisting Pandemics,” social, economic and political factors are equally important. On its own, medical science is not enough.

Syphilis, AIDS and TB have stuck around

Syphilis is a sexually transmitted disease first identified in 1495. It causes skin rashes and may progress to causing paralysis, blindness or both. For centuries, syphilis weakened nations by disabling parents, workers and soldiers in the prime of their lives. Innovative drugs – first Salvarsan (1909), then penicillin (1943) – offered a path toward eradication when used together with widespread testing.

Poster reads 'Both of these men had SYPHILIS' and pictures a healthy one with a family who got his shots, and a man alone with crutch and blindness who didn't
A 1940s poster focuses on the medical cure for the disease.
National Archives, CC BY

Public health programs conducted from the 1930s through the 2000s, however, failed – not because of the efficacy of the treatments but because of socioeconomic conditions.

One challenge has been persistent stigma around getting tested for the disease and tracing sexual partners. Poverty is another; it can force women into commercial sex activities and prevent people from learning how to protect themselves from sexually transmitted infections. Population migration due to commerce or war can cause high-risk behaviors such as sexual promiscuity. Women in some cultures lack authority to negotiate for condom use. And governments have not consistently prioritized the sustained funding needed to support efforts to eliminate the disease.

Despite societal indifference toward syphilis, in the 2020s over 8 million new cases occur globally each year, particularly among racial minorities and low-income populations.

The history of HIV/AIDS is shorter than that of syphilis, but the trajectory has similarities. Doctors first described HIV/AIDS in 1981, when it was a nearly uniformly fatal sexually transmitted disease. Novel antiretroviral drugs introduced in 1996 offered medical scientists the hope of disease elimination through public health campaigns, centered on widespread testing and treatment, implemented in 2013.

But these programs, for reasons like with syphilis, are not meeting their treatment targets across all countries, especially among low-income populations and racial minorities. Sustaining funding for health care infrastructure and the multidrug regimens for 39 million people living with HIV poses an added challenge. Today, despite a cavalier public attitude toward the disease, AIDS causes over 630,000 deaths globally. That number will likely increase substantially given the Trump administration’s decision to cut funding for United States Agency for International Development programs.

Tuberculosis is a third disease that also depleted workforces and weakened nations, particularly in postindustrial revolution 19th-century cities. The disease spread widely because poverty placed people in poorly ventilated working conditions and crowded tenement dwellings. The development of new combination antimicrobial drug regimens offered an avenue for disease eradication in the 1960s.

Nonetheless, the inability to sustain funding to complete complex treatment courses, problems isolating people who could not afford suitable homes, and poor adherence due to homelessness, incarceration or migration during war or trade have compromised public health campaigns. Despite societal nonchalance, tuberculosis today kills up to 1.6 million globally yearly.

two EMTs in PPE rush a patient on a stretcher away from ambulance
Memories of the early, emergency phase of the COVID-19 pandemic have faded.
Stan Grossfeld/The Boston Globe via Getty Images

The COVID-19 case study

The trajectories of these epidemics show how campaigns based solely on biomedical approaches that target pathogens are not enough to eliminate disease.

COVID-19 provides the latest example. In the U.S., the pandemic and its lockdowns disproportionately affected low-income people and racial minorities, especially those employed in front-line jobs that did not allow remote work from home. These groups were more likely to reside in crowded residences with poor ventilation or no space for isolation.

Despite the rapid development of a breakthrough mRNA vaccine that offered hope for what President Joe Biden euphorically termed “independence from the virus,” the promise never fully materialized.

Too few people received shots, in large part due to socioeconomic factors.

Wealthy countries purchased vaccines that lower-income countries could not afford. Allocation difficulties kept vaccines from remote regions of the world.

Vaccine hesitancy due to mistrust in science, along with sentiment that vaccine mandates violated individual freedoms, also prevented people from getting the shot. Similar attitudes reduced rates of mask-wearing and isolation.

Consequently, surges that could have been avoided took more lives.

Drugs and vaccines can’t do it alone

Modern medical science is unmatched in treating pathogens and disease symptoms. But to stop disease, it’s also critical to address the social, economic and political conditions that enable its spread.

Public health officials have started to implement a variety of structural solutions:

several men wearing coveralls watch another man who's holding up a poster
A peer educator talks about HIV/AIDS with his colleagues at a maintenance shop in Kenya.
Wendy Stone/Corbis Historical via Getty Images

Early 20th-century public health officials had hoped that efficient scientific solutions alone could take the place of 19th-century, pre-germ-theory environmental sanitation efforts. COVID-19, syphilis, HIV/AIDS and tuberculosis show that while biomedical breakthroughs are necessary to eliminate epidemic diseases, sustained focus and resources aimed at helping the most socially and economically vulnerable are essential.The Conversation

Powel H. Kazanjian, Professor of Infectious Diseases and of History, University of Michigan

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How Trump’s tariffs could mean rising costs for families, strain for states

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theconversation.com – Bedassa Tadesse, Professor of Economics, University of Minnesota Duluth – 2025-03-04 16:12:00

A potential $110B economic hit: How Trump’s tariffs could mean rising costs for families, strain for states

A worker at a steel company in Monterrey, Nuevo Leon, Mexico, on Feb. 11, 2025.
Julio Cesar Aguilar/AFP via Getty Images

Bedassa Tadesse, University of Minnesota Duluth

Get ready to pay more for avocados, maple syrup and – well – almost everything.

The U.S. officially imposed new 25% tariffs on Canada and Mexico on March 4, 2025, following through on a long-delayed pledge from President Donald Trump. American consumers and businesses are now bracing for higher costs and potential supply disruptions.

Although tariffs, or taxes on imports, are a pillar of Trump’s economic policy, the move still surprised many observers, since Mexico and Canada are among the U.S.’s traditional allies and top trading partners. The administration further rattled global supply chains by doubling existing tariffs on Chinese goods to 20%.

As an economist who studies global trade, I wanted to know how the 25% import duties on Canada and Mexico would affect different parts of the country. So I conducted a state-by-state impact analysis.

What I found is alarming: The U.S. economy could face an annual loss of US$109.23 billion. This shortfall would mean rising costs of everyday goods for American families and would disproportionately affect certain states. My analysis focused exclusively on the effects of U.S. tariffs, so it didn’t take retaliation from Canada or Mexico into account. If it did, the losses would be even greater.

Unequal burdens for states, higher prices for families

Imagine your grocery bill surging by 17.5% to 25%, car parts costing hundreds of dollars more, and your favorite local restaurant raising prices as imported ingredients become unaffordable. Because tariffs drive up consumer prices, these scenarios, or others like them, will soon become reality across the U.S.

But not all Americans will be affected equally, I found. States that are deeply connected to North American supply chains will suffer the biggest economic blows. Texas, with its strong trade ties to Mexico and key role in energy, would lose $15.3 billion. California’s diverse economy would take a $10.2 billion hit. Michigan, heavily reliant on auto manufacturing, would face a $6.2 billion blow – over 1% of its gross domestic product.

The biggest losers from the policy on a per-capita basis would be smaller, trade-dependent states that lack the flexibility to absorb such a shock. New Mexico, Kentucky and Indiana would be among the hardest hit, with projected GDP losses ranging from 1.12% to 1.48%. These states rely heavily on manufacturing and specialized industries, making them particularly vulnerable to rising costs and supply chain disruptions.

Take New Mexico. While it may not experience the largest total economic loss, it would bear the highest per-person burden. That $1.73 billion hit to its economy would translate to $822 for every resident – a devastating blow in a state where incomes are already below the national average.

Indeed, the likely effects of tariffs will be felt especially hard by American families. For example, a family of four in New Mexico would see an estimated $3,288 additional annual costs, equivalent to three months of grocery bills or an entire year’s utility expenses. Families in Kentucky and Indiana would also bear heavy financial burdens, paying an extra $3,120 and $2,836, respectively. Even in wealthier states such as Texas, the added annual costs would reach over $2,000 per household.

For middle- and lower-income families, these aren’t trivial costs. They represent difficult trade-offs, forcing households to cut back on essentials, delay major purchases or dip into savings to make ends meet.

Two flags fly in front of a vehicular bridge.
A truck crosses the Ambassador Bridge, a border crossing between Windsor, Ontario, Canada, and Detroit, Mich., on March 1, 2025.
Geoff Robins/AFP via Getty Images

Where industry will face a tough hit

Perhaps no industry would suffer more than the auto sector, particularly in states such as Michigan, Indiana and Kentucky. These regions rely on a highly integrated North American supply chain, where components cross borders multiple times before a final product reaches consumers. Tariffs would disrupt this delicate balance, leading to price increases, reduced production and job losses.

My conservative estimate shows that such disruptions could cost the industry approximately $28.2 billion, putting around 680,000 jobs at risk across manufacturing, parts production and sales operations. And the ripple effects would extend beyond automakers to suppliers, dealerships and local economies.

But the pain wouldn’t stop there. Manufacturing, which plays a critical role in 17 of the top 20 states most affected by tariffs, would also face rising costs and shrinking profit margins. The agricultural sector – vital in at least 10 states – would endure higher input costs and potential retaliatory tariffs from Mexico and Canada. Past trade disputes have shown that American farmers often bear the brunt of such policies, with lost export markets and declining revenues.

During the U.S.-China trade war of 2018-2019, for example, American farmers suffered over $27 billion in losses, with soybean exports dropping by 71% and states such as Iowa, Illinois and Kansas losing billions in GDP. The federal government paid affected farmers more than $23 billion to offset these losses. Similar – and possibly worse – challenges loom now.

Retaliation from Mexico and Canada could deal a heavy blow to agricultural exports – including corn, beef and dairy – that anchor local economies, especially in Iowa, Nebraska and Wisconsin. Both countries have threatened countermeasures targeting key U.S. exports, raising concerns among farmers and agribusinesses. Retaliatory tariffs could shrink profit margins, further disrupt supply chains, and create uncertainty for producers relying on these markets.

Looking at the bigger picture

The new Trump tariff regime represents a fundamental shift in how the U.S. engages with its closest economic partners. While ostensibly meant to strengthen American industry, the tariffs on offer have serious side effects that will likely cause widespread disruptions for businesses, consumers and entire state economies.

Trade isn’t just about numbers on a spreadsheet. It’s about real people, real businesses and the intricate economic fabric that connects the nation. Changes to this system can come at a high price. Safeguarding American jobs and ensuring economic stability entails recognizing the realities of global trade and considering the trade-offs of instituting new policies.

While tariffs are one method of disrupting the status quo, they are far from the only way. Indeed, reform is also possible through targeted policies – including negotiated trade agreements, investment incentives and workforce development programs – that address trade concerns without altering deeply integrated supply chains.The Conversation

Bedassa Tadesse, Professor of Economics, University of Minnesota Duluth

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