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Rocks on Rapa Nui tell the story of a small, resilient population − countering the notion of a doomed overpopulated island

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theconversation.com – Carl Lipo, Professor of Anthropology and Associate Dean for Research, Binghamton University, University of New York – 2024-06-21 13:05:50
Covering the ground with rocks is actually a good way to grow some crops in poor soil.
Carl Lipo

Carl Lipo, Binghamton University, State University of New York

Conventional wisdom that the island of Rapa Nui, also known as Easter Island, once had a large population that crashed after living beyond its means and stripping the island of resources. A new research study my colleagues and I conducted has struck another blow to this notion by using artificial intelligence to analyze satellite data about piles of rocks on this tiny island in the middle of the Pacific Ocean.

Our study looked at rock gardens, a form of subsistence farming, and determined that the island – just 15.3 miles (24.6 km) long by 7.6 miles (12.3 km) at its widest point – likely never held many more than the 3,000 or so people European explorers encountered in 1722.

The conventional wisdom grew out of speculation about another set of stone structures on the island: the iconic massive statues, called moai, that ancestors of Rapanui people carved. The statues tower as high as a three-story building and weigh up to 70 tons. There are nearly 1,000 of them across the island.

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For an archaeologist, the mystery of what led people to invest so much time and energy in building these colossal figures begs for an explanation. For the past 24 years, my colleagues and I have been searching for one.

Some of the earliest European visitors assumed that the island must have hosted a much larger population at one point to account for the number and magnitude of the moai. This assumption has been repeated for generations and forms the basis of a collapse narrative.

The collapse story holds that the island must have once had tens of thousands of inhabitants needed for the labor involved in carving and transporting the massive statues. Such a large population was not sustainable, and ultimately shortfalls in food resulted in starvation, warfare and even cannibalism. Consequently, the population plummeted to the meager numbers observed by the early European explorers.

large stone carved heads sit on a grassy treeless aside
Did it really take an excessively large population to carve and transport these giant stone statues centuries ago?
AP Photo/Karen Schwartz

In our previous studies of the island my colleagues and I asked ourselves, if there were so many people living on the island at some point before European arrival, where is the evidence? We undertook a new study to examine whether such a large population was possible, given how Rapanui people used rock gardens to grow much of their food. From our evaluation of the available data, our best estimate is that there were never more than 3,000 to 4,000 people, and they lived sustainably on the island.

What rocks say about farming

In this study, we examined the archaeological record of how the Rapanui used rock gardening to grow their main crop, the sweet potato. Rock gardening is a form of cultivation in which broken pieces of bedrock are added to the soil to enrich it. Extensive rock garden cultivation plots are found across the island and would have provided a critical food source augmented by marine resources.

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Previous studies have noted the extent of these gardens and concluded that these efforts might have supported up to 16,000 people. Our fieldwork, however, found that many of the that this study identified as rock gardens were misidentified. So we needed to conduct a more detailed analysis to get a better estimate of rock gardening, which would give us a more reliable source of information about maximum possible population sizes.

We combined fieldwork with new analyses of satellite imagery. During our fieldwork, we looked on the ground for clear examples of rock gardening. We knew we were at locations of rock gardening when we found patches covered with rocks in places that could not be easily explained as the result of erosion. Obsidian artifacts among the rocks confirmed that the areas were used for cutting and processing sweet potatoes. Often, these areas have another root crop, taro, growing in them even . We also identified places that might resemble rock mulch gardens but were just bedrock outcrops or random scatters of cobbles and boulders.

We then acquired WorldView-3 satellite imagery for the entire island. The WorldView-3 satellite collects high-resolution visible light photos of the Earth's surface and images that record shortwave infrared information. Shortwave infrared includes wavelengths that range between 900 nm and 2,500 nm, longer than are visible to the human eye. Shortwave infrared is helpful for distinguishing materials that look identical to the unaided eye. In particular, shortwave infrared is sensitive to differences in moisture, an essential attribute of productive agricultural fields.

Using our field data, we trained machine learning models to distinguish rock mulch gardening areas from those that are not. Machine learning generates an algorithm that can detect subtle differences – and can do so repeatedly and systematically. In this way, we could examine nearly the entire island quickly and without spending years doing field mapping.

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A map of a triangular shaped island
Red dots indicate rock gardens detected by satellite imagery.
Dylan Davis, CC BY

Our analyses dramatically reduced the island's total area that can be associated with rock gardening, from a range of 1.6 to 8.1 square miles (4.3 to 21.1 square kilometers) down to 0.29 square miles (0.76 square kilometers). When we entered estimates for the productivity of these areas, our calculations showed that the maximum number of people this form of cultivation can is about 3,000, quite similar to the conclusions we reached with other sources of information.

Resilience rather than hubris

Over the past 20 years, researchers have generated significant new evidence about the archaeological record of Rapa Nui, contributing to reframing the island's narrative away from the idea of collapse. For example, studies from my team demonstrate that the statues were moved in a walking fashion from the quarry to their final locations on platforms called ahu. We have also tackled the question of how the islanders placed giant multiton hats called pukao on the tops of these statues.

However, the idea that there were much larger numbers of people on the island remains embedded in the academic and popular literature. The persistence of this idea has consequences outside of the field of Rapa Nui archaeology. Despite archaeological evidence to the contrary, it is not uncommon, for example, for ecologists to use Rapa Nui as a case study of so-called Malthusian demographics, where the population is assumed to have reached a massive peak that momentarily outstripped the island's resources and triggered an ecological catastrophe.

While my colleagues and I agree that it is essential to be concerned about the potential for exploitation of natural resources, catastrophe is not the only possibility. Human history offers many examples demonstrating how it is possible to sustainably despite constraints.

On Rapa Nui, we have learned that its people did not experience a population collapse before the arrival of Europeans but instead succeeded due to their ingenuity. Rapanui people found clever ways of adapting to the island and practiced sustainable farming to support themselves. This research adds details about the capacity of rock gardens to grow food and support the population of the island.

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A pile of rocks on a sunny treeless hillside
Rock gardens add nutrients and retain moisture in poor soil.
Carl Lipo

Our increasing understanding of the island has critical implications for the future. In learning how to thrive in a limited , society can adopt strategies used by people in the past. The archaeological record of Rapa Nui points to the idea that efforts that bring communities together in cooperative and competitive ways, such as moai carving and transport, to greater resiliency in times of shortfall.

In the end, the history of Rapa Nui is not a cautionary tale but a source of inspiration that may be key to humanity's future.The Conversation

Carl Lipo, Professor of Anthropology and Associate Dean for Research, Binghamton University, State University of New York

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

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The Conversation

Supermassive black holes have masses of more than a million suns – but their growth has slowed as the universe has aged

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theconversation.com – Fan Zou, Graduate Student in Astronomy and Astrophysics, Penn – 2024-07-12 07:33:14
Most of the blue points in this sky survey image are accreting supermassive black holes emitting strong X-rays.
Fan Zou (Penn State) and the XMM-SERVS Collaboration

Fan Zou, Penn State and W. Niel Brandt, Penn State

Black holes are remarkable astronomical objects with gravity so strong that nothing, not even light, can escape them. The most gigantic ones, known as “supermassive” black holes, can weigh millions to billions times the mass of the Sun.

These giants usually live in the centers of galaxies. Our own galaxy, the Milky Way, contains a supermassive black hole in its heart as well.

So, how do these supermassive black holes become super massive? To answer this question, our team of astrophysicists looked back in time across the universe's 13.8 -year history to track how supermassive black holes have grown from the early days to .

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We constructed a model of the overall growth history of supermassive black holes spanning the past 12 billion years.

How do supermassive black holes grow?

Supermassive black holes grow primarily in two ways. They can consume gas from their host galaxies in a process called accretion, and they can also merge with each other when two galaxies collide.

A black hole, shown as a dark dot in a swirling spiral of clouds.
An artist's illustration of an accreting supermassive black hole. The central black hole is black, while its surrounding gas heats up and shines to produce light.
Nahks Tr'Ehnl (Penn State)

When supermassive black holes consume gas, they almost always emit strong X-rays, a type of high-energy light invisible to the naked eye. You've probably heard of X-rays at the dentist, where they are sometimes used to examine your teeth. The X-rays used by astronomers generally have lower energies than medical X-rays.

So how can any light, even invisible X-rays, escape from black holes? Strictly speaking, the light is not coming from the black holes themselves, but from the gas just outside them. When gas gets pulled toward a black hole, it heats up and shines to produce light, like X-rays. The more gas a supermassive black hole consumes, the more X-rays it will produce.

Thanks to the data accumulated over more than 20 years from three of the most powerful X-ray facilities ever launched into Chandra, XMM-Newton and eROSITA – astronomers can capture X-rays from a large number of accreting supermassive black holes in the universe.

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This data allows our research team to estimate how fast supermassive black holes grow by consuming gas. On average, a supermassive black hole can consume enough gas to amount to about the mass of the Sun each year, with the exact value depending upon various factors.

For example, the data shows that a black hole's growth rate, averaged over millions of years, is strongly connected to the mass of all the in its host galaxy.

How often do supermassive black holes merge?

Besides feeding on gas, supermassive black holes can also grow by merging with each other to form a single, more massive black hole when galaxies collide.

Supercomputer cosmological simulations can predict about how often these happen. These simulations aim to model how the universe grows and evolves over time. The countless galaxies flying through space are kind of like bricks, building up the universe.

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These simulations show that galaxies and the supermassive black holes they host can undergo multiple mergers across the span of cosmic history.

Our team has tracked these two growth channels – gas consumption and mergers – using X-rays and supercomputer simulations, and then combined them to construct this overall growth history, which maps the growth of black holes across the universe over billions of years.

Our growth history revealed that supermassive black holes grew much faster billions of years ago, when the universe was younger.

Back in the early days, the universe contained more gas for supermassive black holes to consume, and supermassive black holes kept emerging. As the universe aged, the gas was gradually depleted, and supermassive black hole growth slowed. About 8 billion years ago, the number of supermassive black holes stabilized. It hasn't increased substantially since then.

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Two small dark dots surrounded by gas clouds rotate near each other.
An illustration of a merger of two supermassive black holes.
Scott Noble (NASA GSFC)

When there isn't enough gas available for supermassive black holes to grow by accretion, the only way for them to get larger is through mergers. We didn't see very many cases of that in our growth history. On average, the most massive black holes can accumulate mass from mergers at a rate up to the mass of the Sun every several decades.

Looking forward

This research has helped us understand how over 90% of the mass in black holes has accumulated over the past 12 billion years.

However, we still need to investigate how they grew in the very early universe to explain the remaining few percentages of the mass in black holes. The astronomical community is starting to make progress exploring these early supermassive black holes, and we hope to find more answers soon.The Conversation

Fan Zou, Graduate Student in Astronomy and Astrophysics, Penn State and W. Niel Brandt, Professor of Astronomy and Astrophysics, Penn State

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

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Meteorites from Mars help scientists understand the red planet’s interior

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theconversation.com – James Day, Professor of Geosciences, of California, San Diego – 2024-07-12 07:32:55
A Martian meteorite in cross-polarized light. This meteorite is dominated by the mineral olivine. Each grain is about half a millimeter across.
James Day

James Day, University of California, San Diego

Of the more than 74,000 known meteorites – rocks that fall to Earth from asteroids or planets colliding together – only 385 or so stones came from the planet Mars.

It's not that hard for scientists to work out that these meteorites from Mars. Various landers and rovers have been exploring Mars' surface for decades. Some of the early missions – the Viking landers – had the equipment to measure the composition of the planet's atmosphere. Scientists have shown that you can see this unique Martian atmospheric composition reflected in some of these meteorites.

Mars also has unique oxygen. Everything on Earth, including humans and the we breathe, is made up of a specific composition of the three isotopes of the element oxygen: oxygen-16, oxygen-17 and oxygen-18. But Mars has an entirely different composition – it's like a geochemical fingerprint for being Martian.

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The Martian meteorites found on Earth give geologists like me hints about the makeup of the red planet and its history of volcanic activity. They allow us to study Mars without sending a spacecraft 140 million miles away.

A planet of paradoxes

These Martian meteorites formed from once red-hot magma within Mars. Once these volcanic rocks cooled and crystallized, radioactive elements within them started to decay, acting as a radiometric clock that enables scientists to tell when they formed.

From these radiometric ages, we know that some Martian meteorites are as little as 175 million years old, which is – geologically speaking – quite young. Conversely, some of the Martian meteorites are older, and formed close to the time Mars itself formed.

These Martian meteorites tell a story of a planet that has been volcanically active throughout its entire history. In fact, there's potential for Martian volcanoes to erupt even , though scientists have never seen such an eruption.

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The rocks themselves also preserve chemical information that indicates some of the major on Mars happened early in its history. Mars formed quite rapidly, 4.5 years ago, from gas and dust that made up the early solar system. Then, very soon after formation, its interior separated out into a metallic core and a solid rocky mantle and crust.

Since then, very little seems to have disturbed Mars' interior – unlike Earth, where plate tectonics has acted to stir and homogenize its deep interior. To use a food analogy, the Earth's interior is like a smoothie and Mars' is like a chunky fruit salad.

Two fume hoods with vials of sample under them.
Martian meteorite samples are prepared for analysis in a clean lab.
James Day

Martian volcano remnants

Understanding how Mars underwent such an early and violent adolescence, yet still may remain volcanically active today, is an area of great interest to me. I would like to know what the inside of Mars looks like, and how its interior makeup might explain features, like volcanoes, on the red planet's surface.

When geologists set out to answer questions about volcanism on Earth, we typically examine lava samples that erupted at different places or times from the same volcano. These samples allow us to disentangle local processes specific to each volcano from planetary processes that take place at a larger scale.

It turns out we can do the same thing for Mars. The rather exotically named nakhlite and chassignite meteorites are a group of rocks from Mars that erupted from the same volcanic system some 1.3 billion years ago.

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Nakhlites are basaltic rocks, similar to lavas you would find in Iceland or Hawaii, with beautiful large crystals of a mineral known as clinopyroxene. Chassignites are rocks made almost entirely of the green mineral olivine – you might know the gem-quality variety of this mineral, peridot.

Along with the much more common shergottites, which are also basaltic rocks, and a few other more exotic Martian meteorite types, these categories of meteorite constitute all the rocks researchers possess from the red planet.

When studied together, nakhlites and chassignites tell researchers several things about Mars. First, as the molten rock that formed them oozed to the surface and eventually cooled and crystallized, some surrounding older rocks melted into them.

That older rock doesn't exist in our meteorite collection, so my team had to tease out its composition from the chemical information we obtained from nakhlites. From this information, we learned that the older rock was basaltic in composition and chemically distinct from other Martian meteorites. We found that it had been chemically weathered by exposure to and brine.

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This older rock is quite different from the Martian crust samples in our meteorite collection today. In fact, it is much more like what we would expect the Martian crust to look like, based on data gathered by rover missions and satellites orbiting Mars.

We know that the magmas that made nakhlites and chassignites come from a distinct portion of Mars' mantle. The mantle is the rocky portion between Mars' crust and metallic core. These nakhlites and chassignites come from the solid rigid shell at the top of Mars' mantle, known as the mantle lithosphere, and this source makes them distinct from the more common shergottites.

Shergottites come from at least two sources within Mars. They may come from parts of the mantle just beneath the lithosphere, or even the deep mantle, which is closer to the planet's metallic core.

alt
The interior structure of Mars, with the sources of meteorites indicated.
James Day

Understanding how volcanoes on Mars work can inform future research questions to be addressed by missions to the planet. It can also scientists understand whether the planet has ever been habitable for , or if it could be in the future.

Hints at habitability

Earth's active geological processes and volcanoes are part of what makes our planet habitable. The gases emanating from volcanoes are a major part of our atmosphere. So if Mars has similar geological processes, that could be good news for the potential habitability of the red planet.

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Mars is much smaller than Earth, however, and studies suggest that it's been losing the chemical elements essential for a sustainable atmosphere since it formed. It likely won't look anything like Earth in the future.

Our next steps for understanding Mars lie in learning how the basaltic shergottite meteorites formed. These are a diverse and richly complex set of rocks, ranging in age from 175 million years to 2.4 billion years or so.

Studying these meteorites in greater detail will help to prepare the next generation of scientists to analyze rocks collected using the Perseverance Rover for the forthcoming NASA Mars Sample Return mission.The Conversation

James Day, Professor of Geosciences, University of California, San Diego

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

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Storytelling strategies make communication about science more compelling

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theconversation.com – Emma Frances Bloomfield, Associate Professor of Communication Studies, University of Nevada, Las Vegas – 2024-07-11 07:26:49
A story that includes characters and focuses on what people care about can stand up to misinformation.
SDI Productions/E+ via Getty Images

Emma Frances Bloomfield, University of Nevada, Las Vegas

As a science communication scholar, I've always supported vaccination and trusted medical experts – and I still do. As a new mom, however, I've been confronting new-to-me emotions and concerns while weighing decisions about my son's health.

Vaccines are incredibly effective and have minimal risks of side effects. But I began to see why some parents may hesitate because of the flood of content, especially online, about potential vaccine risks.

Part of what makes vaccine misinformation persuasive is its use of storytelling. Antivaccine advocates share powerful personal experiences of childhood illnesses or alleged vaccine side effects. It is rare, however, for scientists to use the same storytelling strategies to counter misinformation.

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In my book “Science v. Story: Narrative Strategies for Science Communicators, I explore how to use stories to in a compelling way about controversial science topics, vaccination. To me, stories contain characters, action, sequence, scope, a storyteller, and content to varying degrees. By this definition, a story could be a book, a article, a social media post, or even a conversation with a friend.

While researching my book, I found that stories about science tend to be broad and abstract. On the other hand, science-skeptical stories tend to be specific and concrete. By borrowing some of the strategies of science-skeptical stories, I argue that evidence-backed stories about science can better compete with misinformation.

To make science's stories more concrete and engaging, it's important to put people in the story, explain science as a , and include what people care about.

woman and man with arms around each other looking at burned out house site
Stories hit home more when they include human characters and not just forces of nature.
VladTeodor/iStock via Getty Images Plus

Put people in the story

Science's stories often lack characters – at least, human ones. One easy way to make better stories is to include scientists making discoveries or performing experiments as the characters.

Characters can also be people affected by a scientific topic, or interested in learning more about it. For example, stories about climate change can include examples of people feeling the effects of more extreme weather events, such as the devastating impacts of California wildfires on local communities.

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Characters can also be storytellers who are sharing their personal experiences. For example, I started this article with a brief discussion of my personal vaccine decisions. I was not a hidden or voiceless narrator, but someone sharing an experience that I hope others can relate to.

Explain science as a process

People often think of science as objective and unbiased. But science is actually a human practice that constantly involves choices, missteps and biases.

At the beginning of the pandemic, for example, the medical advice was not to mask. Scientists initially thought that masks didn't prevent transmission of the SARS-CoV-2 virus that causes COVID-19. However, after additional research, medical advice changed to masking, providing the public with the most updated and accurate knowledge.

If you explain science as a process, you can walk people through the sequence of how science is done and why researchers reach certain conclusions. Science communicators can emphasize how science is conducted and why people should trust the process of science to provide the most accurate conclusions possible given the available information.

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Include what people care about

Scientific topics are important, but they may not always be the public's most pressing concerns. In April 2024, Gallup found that “the quality of the ” was one of the lowest-ranked priorities among people in the U.S. Of those polled, 37% said they cared a great deal about it. More immediate issues, such as (55%), and violence (53%), the economy (52%), and hunger and homelessness (52%) ranked much higher.

Stories about the environment could weave in connections to higher-priority topics to emphasize why the content is important. For example, stories can include information about how mitigating climate change can work hand in hand with improving the economy and creating jobs.

Medical provider faces woman and child, in discussion
A pediatrician is a science communicator, and so is a parent who talks about their own medical experiences.
SDI Productions/E+ via Getty Images

Telling science's stories

Scientists, of course, can be science communicators, but everyone can tell science's stories. When we share information online about health, or talk to friends and family about the weather, we contribute to information that circulates about science topics.

My son's pediatrician was a science communicator when she explained the vaccine schedule and ways to keep my son comfortable after receiving vaccines. I was a science communicator when I spoke to others about my decisions to fully vaccinate my son on the recommended schedule, and how he is now a healthy and happy 9-month-old.

When communicating about science topics, remember to borrow features from stories to strengthen your message. Think about all of a story's features – character, action, sequence, scope, storyteller and content – and how you might incorporate them into the topic. Everyone can find opportunities to strengthen their science communication, whether it's in their or in their everyday interactions with friends and family.The Conversation

Emma Frances Bloomfield, Associate Professor of Communication Studies, University of Nevada, Las Vegas

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