Wider World by CS: เหรียญเงินหลวงพ่อแดงรุ่นแรก

Wider World by CS: เหรียญเงินหลวงพ่อแดงรุ่นแรก: ตามประวัติการผลิตแจ้งว่าเหรียญรุ่นนี้มีประมาณแปดสิบกว่าเหรียญ ผู้เขียนได้มานานมากแล้วประมาณสามสิบกว่าปีและไม่ได้ให้ความใส่ใจมาก ปัจจุบันำม...

เหรียญเงินหลวงพ่อแดงรุ่นแรก

ตามประวัติการผลิตแจ้งว่าเหรียญรุ่นนี้มีประมาณแปดสิบกว่าเหรียญ
ผู้เขียนได้มานานมากแล้วประมาณสามสิบกว่าปีและไม่ได้ให้ความใส่ใจมาก
ปัจจุบันำมาล้างใหม่และเริ่มสนใจตรวจสอบจริงจังในความแท้ของเหรียญ

วันนี้นำมาลงให้ชม ทั้งสภาพก่อนล้างและหลังล้างเหรียญ
เหรียญรุ่นนี้มีจุดตายที่  กระดูกไหปาร้าของหลวงพ่อต้องมีล่อง/ที่ขอบหูเหรียญต้องมีขีดยาว/ด้านหลังมีลอยเสี้ยนตะไบ ลองชมดู

ม.โชคชัย

it is getting bigger and bigger

• By Melissa Hogenboom

24 February 2017

Near the Yana river basin, in a vast area of permafrost, there is a dramatic tadpole-shaped hole in the ground: the Batagaika crater.

The crater is also known as a "megaslump" and it is the largest of its kind: almost 0.6 miles (1km) long and 282ft (86m) deep. But these figures will soon change, because it is growing quickly.

Locals in the area avoid it, saying it is a "doorway to the underworld". But for scientists, the site is of great interest.

Looking at the layers exposed by the slump can give indications of how our world once looked – of past climates. At the same time, the acceleration of the growth gives an immediate insight into the impact of climate change on the increasingly fragile permafrost.

The ground here is frozen year-round (Credit: Julian Murton)

There are two types of permafrost. One is from glacier ice, left over from the last Ice Age and now buried underground. The other type, the one present around the Batagaika crater, is ice that has formed in the ground itself. Often, this ice is trapped beneath a layer of sediment and has been frozen for at least two years.

The Batagaika crater opens up a vast area of previously buried permafrost, some of which first formed many thousands of years ago.

During the last 200,000 years, Earth's climate has alternated repeatedly

The trigger that led to the crater started in the 1960s. Rapid deforestation meant that the ground was no longer shaded by trees in the warmer summer months. This incoming sunlight then slowly warmed the ground. This was made worse by the loss of cold "sweat" from trees as they transpire, which would have kept the ground cool.

"This combination of less shading and less vapid transpiration led to warming of the ground surface," says Julian Murton of the University of Sussex in the UK.

As the ground surface warmed up, it caused the layer of soil right above the permafrost to warm. This caused the permafrost itself to thaw. Once this process started and the ice was exposed to warmer temperatures, melting escalated.

For these reasons, scientists are actively monitoring the crater. One study, published in the journal Quaternary Research in February 2017, found that analysing the layers now exposed could reveal 200,000 years of climatic history.

Layers in the slump reveal past climates (Credit: Julian Murton)

During the last 200,000 years, Earth's climate has alternated repeatedly between relatively warm "interglacial" periods and chilly "glacial" periods in which ice sheets expanded.

The Batagaika sediment layers provide a "continuous record of geological history, which is fairly unusual," he says. "That should allow us to interpret the climate and environmental history there."

The climatic history of a huge part of Northern Siberia is little understood

However, for now the dates are not certain. "We are still working on the chronology," says Murton.

Next, he needs to gather and analyse more sediments. Ideally, these will be collected using a drill in order to get a "continuous sediment series", which will help give more accurate dates. The permafrost record could then be compared with data from other temperature records, such as ice-cores from ice sheets.

"Ultimately, we're trying to see if climate change during the last Ice Age [in Siberia] was characterised by a lot of variability: warming and cooling, warming and cooling as occurred in the North Atlantic region," says Murton.

This is important, because the climatic history of a huge part of northern Siberia is little understood. By reconstructing environmental changes that happened in the past, scientists could help forecast similar changes.

The crater grows more each year (Credit: Alexander Gabyshev)

For example, 125,000 years ago, the climate was going through an interglacial period, during which it was several degrees warmer than it is now. "If we can understand what the ecosystem was like then – that might give us some inkling into how the environment may change now if the climate is warming," says Murton.

We now know that this permafrost is changing fast

If the permafrost responds to warming in a similar way as it did after the last Ice Age, we can expect to see many more slumps, big basins and lakes forming.

New land may even start to appear, as thawed ice exposes buried land some 33-66ft (10-20m) below the original surface. "You have this very ice-rich permafrost that starts to thaw from the top downwards as the ice drains and melts, and so we get a new landscape develop," says Murton.

These impacts may not be all that far off. We now know that this permafrost is changing fast.

Melting permafrost could speed up climate change (Credit: Julian Murton)

Frank Günther of the Alfred Wegener Institute in Potsdam, Germany, and colleagues have been monitoring the site for the last decade, using satellite images to measure the rate of change.

Continuous growth means that the crater gets deeper and deeper every year

During their study, the head wall of the crater has grown by an average of 33ft (10m) per year. In warmer years, the changes have been even greater, sometimes up to 98ft (30m) per year. Günther announcedthese findings at the American Geophysical Union meeting in December 2016.

He also has reason to believe that the side wall of the growing crater will reach a neighbouring eroding valley in the coming summer months. This in turn will "very likely" be a new trigger for more growth.

"On average over many years, we have seen that there's not so much acceleration or deceleration of these rates, it's continuously growing," says Günther. "And continuous growth means that the crater gets deeper and deeper every year."

This has other worrying consequences.

Remnants of ancient forests are preserved in the permafrost (Credit: Julian Murton)

Many of the ice deposits that are now being exposed formed during the last Ice Age. This ground ice contains a lot of organic matter, including plenty of carbon that has been locked away for thousands of years.

"Global estimations of carbon stored in permafrost is [the] same amount as what's in the atmosphere," says Günther.

There is no indication that the erosion of this crater will slow down any time soon

As more permafrost thaws, more and more carbon is exposed to microbes. The microbes consume the carbon, producing methane and carbon dioxide as waste products. These greenhouse gases are then released into the atmosphere, accelerating warming further.

"This is what we call positive feedback," says Günther. "Warming accelerates warming, and these features may develop in other places. It's not only a threat to infrastructure. Nobody can stop this development. There's no engineering solution to stop these craters developing."

There is no indication that the erosion of this crater will slow down any time soon, as it continues to grow year on year.

That makes the future of Siberia's permafrost look very wobbly indeed.

Melissa Hogenboom is BBC Earth's feature writer. She is @melissasuzanneh on Twitter.

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12 Ways to Take Control of Your Life

It seems, more often than not, that exhaustion and achievement go hand in hand. But a burn-out is no symptom of success, it's your body's way of telling you to slow down. A short quick fix may seem like a good solution, but in order to get to the root of the problem, fundamental change takes time. These 12 powerful ways will help you take charge of your destiny and transform your life.

1. Get all the sleep you need
A good night's sleep cleans your brain of toxins that build up during the day, studies show. Aim to get a full seven to eight hours of sleep, by getting just 30 minutes more sleep than you are getting now, be that at nighttime or a midday nap.

2. Be mindful while you eat
Studies show that mindful eating can lift your mood, decrease stress, and promote weight loss. But, mindful eating takes practice. It challenges you to consider the essence of everything you consume - where it came from, the nutritional benefits it has on your body, and how your food got to your plate. Mindful eating focuses on building a healthy, sustainable relationship with food. 

3. Skip the caffeine
Being a stimulant, caffeine directly affects your central nervous system. Consuming too much coffee can make your heart race and head pound. If you're feeling anxious, stressed, or burned out, coffee isn't your long term fix. Rather, opt for something that offers a long term solution, such as exercise or meditation, to help you feel energized and awake. 

4. Get (and stay) active
There's no better mood-booster and stress-reducer than movement. Exercise has been shown to protect memory and thinking skills. Exercising in the morning can help set the pace for the rest of the day, sharpening your focus. Try getting an extra 10 minutes of moderate activity each day, slowly working your way up to the recommended 30 minutes daily. 

5. Take comfort in silence
Meditation really works. Around 80% of doctor's visits are due to stress-related problems. Meditation has been found to reduce stress, boost immunity, improve sleep, and, possibly, increase happiness. People who meditate are generally less anxious when confronted with challenges. 

6. Take care of your skin
Forming healthy skin care habits does take time. Consistency, repetition, and embracing your new routine will do a lot of good for your skin. Opt for products and foods that naturally nourish the skin and follow through with a daily and nightly skin care ritual that will make you feel healthy and beautiful. Over time, you will begin to notice a lift in your skin.  

7. Do things that make you happy
As the saying goes: 'Starve your ego and feed the soul.' Just because something brings you a sense of achievement, it does not necessarily mean that it will fill you with joy. Whatever you choose to do, do so because it makes you happy, not because it's something to mark off your to-do list. 

8. Listen to your intuition
Listen to that persistent gut feeling when making a big decision. Your body will tell you what it wants from you before you need it. If you're feeling tired, take a nap. If you're in need of a vacation, go on a trip. If something doesn't feel quite right, look into it. Listening to your gut does take practice. Be patient and it will pay off. 

9. Mix things up
Routine can be beneficial on occasion. Though every now and then, challenge yourself to do something completely new at least once a week. It could be as simple as walking a new route to work, or starting the blog you always said you would. New experiences open your mind to new ways of thinking and perceiving, making you happier. 

10. Surround yourself with positivity
Build healthy relationships by being mindful of whom you fill your life with. Take time to reassess your relationships and consider the value they add to your life and well-being. People who are mindful of their relationships tend to be more confident in their judgment. 

11. Take the time to learn something new
Learning new things have the capacity to make us happy. They could also enable us to live longer, stay open-minded, and live our lives more fully. Whatever you decide to learn, in the long run you will gain from keeping your brain sharp and young. 

12. Keep a journal
Journal writing has been shown to relieve stress, boost comprehension, spark creativity, build confidence, and encourage you to accomplish your goals. You need not put too much pressure on yourself to write daily. The writing process itself is more important than how often you write. You can choose to write first thing in the morning, using a prompt like, 'how do I want my day to be?', or before bed time, releasing all of your anxious thoughts. 

Where does the Trump saga end?

Matt Bai 

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President Trump at a news conference in the White House on Feb. 16. (Photo: Mark Wilson/Getty Images)

Where is all this headed, and how does it end?

These are the questions you hear all over Washington right now. Which is strange, because normally you wouldn’t be idly speculating about the end of a presidency barely a month after the inauguration. Certainly, in parts of the country that voted overwhelmingly for Trump, the sense is he’s just getting started.

But the pervasive view in the capital is that President Trump at this point is like a guy behind the wheel who hasn’t slept in a week, surrounded by a small mountain of empty Red Bull cans as he weaves his way across four lanes at night, squinting to read the signs and ignoring the angry blasts of horns.

Sure, it’s a straight drive home on a sparsely populated highway. But at this rate, what are the odds he makes it very far without hurting himself … or someone else?

Some of this is just the lingering shock of the election. A lot of people in Washington are still waking up every morning with a feeling of “this cannot be happening,” and from there it’s a short jump to “this cannot go on for very long.”

But it’s also the sense that Trump himself has skipped right over the opening and middle stages of a normal presidency — honeymoon, legislative push, midterms and reelection — and leaped straight into the self-pitying, paranoid, scandal-shadowed slog of year seven.

Already he spends half his time golfing in Florida and the other half watching cable TV. While hostile nations brazenly test the boundaries of this new United States of Entropy, the president labels the media “the enemy of the American people,” as if he’s planning to storm the network studios and replace their programming with endless “Apprentice” reruns.

If all of this doesn’t frighten some wide swath of voters, then it’s bound to exhaust them. So it’s reasonable to ponder the fate of the Trump presidency, just weeks into the grand experiment.

Trump could get his act together any day now, dedicate himself to learning the job. If this were a movie, he might have this moment of epiphany at a soup kitchen somewhere when he realizes the nation is depending on him to be a bigger man, and we’d instantly time-cut to three days later, when he’s pored through a raft of presidential biographies and decided to fire his entire staff and start again.

Then again, if this were a movie, it might also be called “The Siberian President,” and it might end with Trump trying to hold off Ben Affleck and a unit of elite Rangers with an AK-47 on the steps of the Lincoln Memorial, shouting epithets in Russian. Either seems equally plausible to me.

Democrats have their own wishful scenario, which involves impeachment. But absent some cataclysmic revelation (like, say, that Trump agreed to hand over all of Ukraine to the Russians in exchange for turning the Kremlin into the most incredible, most elegant five-star resort you’ve ever seen in your life, you wouldn’t believe), it’s hard to imagine a Republican Congress evicting a president who remains a folk hero to its base.

You can more easily see how Trump might talk his administration into total paralysis. If he decides to stay on the current erratic trajectory, and if his approval ratings keep sinking in search of a bottom, a lot of governing Republicans will run from him as fast as they can, and he’ll find himself isolated and unable to achieve much of anything.

Down that path lies an almost certain primary opponent — probably a Marco Rubio or a John Kasich — and the very real possibility that Trump would walk away voluntarily, in order to at least give Mike Pence a fighting chance to succeed him.

Leaving all these possible outcomes aside for the moment, though, the one that seems most likely to me is probably also the most mundane. The presidency isn’t going to change who Trump is, but he may very well end up changing the way we think about the presidency.

Eventually, and not so very far into the future, two things are going to happen. The first is that Trump is going to realize that a White House can’t really run this way — the president at war with the media, aides at war with each other, fictions at war with facts. Someone needs to get control of the operation, and hopefully before an economic or international crisis comes along to make the dysfunction even clearer than it is.

The second is that Trump is going to decide he actually doesn’t like the job very much — or at least not the part of the job that’s all about policy and vote counts and other things you have to think about for more than 90 seconds without changing the subject to yourself.

And that’s the moment when Trump, who knows nothing if not how to bail out failing business ventures, will bow to the protestations of establishment Republicans and retool his administration. He’ll bring in a chief of staff who knows something about day-to-day governing — maybe a Chris Christie or a Haley Barbour, or perhaps a member of his Cabinet, like Nikki Haley.

The fringe ideologues and campaign aides will be relegated to the margins, where they belong. The details of Republican government will be directed by the conventional power centers of Pence, an empowered chief of staff, Mitch McConnell in the Senate and Paul Ryan in the House (with assists from veteran strategists like Newt Gingrich and some big-time lobbyists). Legislation will move; modest deals will be brokered.

All of which will leave Trump to do what he most enjoys and does best: build the brand. He’ll hold rallies, fire off outrageous tweets, commandeer the press room, pop up on late night TV. He’ll convene and bluster. He will be the central character in our national consciousness, but a supporting actor at best in our government.

And if I’m right, and this is what ultimately transpires, then Trump will succeed in redefining the presidency in our time — or, perhaps more accurately, defining it down. We will come to regard him as a forceful figurehead, the outrageous star of the highly rated presidential series, a born performer expertly playing a role for our amusement. Which is pretty much how he started out anyway.

Maybe this is what we deserve, in an era when politics and entertainment have become so deeply intertwined and so hard to differentiate. Maybe, from here on out, the president is destined to become more like a quasi-monarch, asked to form a government and to preside over it, but not necessarily to manage or direct it. Maybe that will be Trump’s lasting innovation.

There was a time when presidents didn’t campaign for the office, after all. There was a time when they didn’t debate, because debating was beneath them.

Perhaps we’ll soon say there was also a time when they didn’t mostly preen and provoke, but actually endeavored to govern instead.

Reviving woolly mammoths

• By Helen Pilcher

22 February 2017

Woolly mammoths are in the news again. According to recent news reports, they are "on the verge of resurrection" and "will be back from extinction within two years." The prompt for this was a statement by the Harvard geneticist George Church, lead scientist for the "Woolly Mammoth Revival" project.

However, in the wake of the excitable reports, other commentators have been urging caution. The palaeontologist John Hawks went so far as to call the reports of the mammoth's imminent revival "fake news".

So are shaggy-coated pachyderms really poised to stampede across the frozen wastelands of Siberia any time soon? If such creatures are created, will they really be mammoths? And even setting aside exactly when this might happen, is it a good idea to bring a species back from the dead?

I am a former cell biologist and have spent the last two years researching and writing about de-extinction, the science of bringing extinct animals back to life. I have spoken with Church, as well as many of the other scientists at the forefront of de-extinction research, and two things are clear to me. The first is that a living, breathing woolly mammoth is far from imminent, and the second is that, nevertheless, the science needed to make it is progressing at quite a lick.

Iberian ibex (Capra pyrenaica), the closest living relative of the bucardo (Credit: John Cancalosi/naturepl.com)

The woolly mammoth would not be the first species to be revived after having been wiped out. The world's first de-extinct animal was born in 2003 in a laboratory in Spain. It was a type of wild mountain goat called a bucardo, or Pyrenean ibex.

The animal only lived for a few short minutes, but since then the science underpinning de-extinction has progressed in leaps and bounds. The researchers who brought back the bucardo tell me that only two things stand between them and a whole herd of healthy de-extinct bucardo: time and money.

Church is not talking about making a living, breathing, fur-coated mammoth calf

Such revivals depend on manipulating basic biology.

An animal's life begins when a single cell splits in two, then keeps on dividing to form a miniscule bundle of cells called an "embryo". In time, the cells of the embryo divide and become more specialised. Different tissues, organs and limbs form, leading eventually to a complete living animal.

Anyone wanting to make a woolly mammoth must first create a single mammoth cell, coax it into becoming an embryo, and then nurture that embryo while it grows into an entire mammoth.

Speaking ahead of this week's annual meeting of the American Association for the Advancement of Science (AAAS) in Boston, Church said he thought he was a couple of years away from making an embryo. In my opinion, this is entirely possible, but only so long as you pay close attention to what Church is claiming.

The first thing to bear in mind is that Church is not talking about making a living, breathing, fur-coated mammoth calf. His work so far focuses solely on single cells.

Partially-frozen tundra in Siberia (Credit: Sergey Gorshkov/naturepl.com)

For the last few years, Church and his team have been carefully placing mammoth genes into the cells ofAsian elephants, woolly mammoths' closest living relatives. They are endowing these elephant cells with the "essence of mammoth": the potential to grow long, luscious locks, lay down Sumo-wrestler-sized rolls of body fat, and other characteristics that should help the animal to look and act like a mammoth.

It will be an animal whose DNA is largely elephant, but with a smattering of judiciously-placed mammoth DNA

When I spoke to Church in 2015, he had already added in the gene for mammoth haemoglobin. Haemoglobin is the molecule in red blood cells that ferries oxygen around the body. The mammoth version works even at low temperatures; essential for an animal, like the woolly mammoth, that evolved during an ice age.

It is now two years later and Church's team have made 45 changes to the elephant genome. They are moving closer to their goal of "mammoth-ifying" an elephant cell.

But they may have a long way to go. A 2015 study compared the woolly mammoth genome with that of living Asian elephants, and identified changes in 1,642 genes. Church's 45 changes amount to a small fraction of that total, but Church argues that he does not need to put every single tweak into his elephant cells to make something mammoth-like.

Asian elephants (Elephas maximus) are similar to mammoths (Credit: Yashpal Rathore/naturepl.com)

Church has never claimed that he is making a bona-fide, genuine, 100% authentic woolly mammoth. Instead it will be an animal whose DNA is largely elephant, but with a smattering of judiciously-placed mammoth DNA.  

He talks of making a "mammoth-elephant hybrid" or a "cold-adapted elephant". I prefer to call it a "mammophant" or "elemoth".

In order to make a mammophant embryo, Church's team will also need to advance the science of cloning

Assuming Church manages to create a mammophant cell, the next step will be to convert it into a mammophant embryo. One way to do this is to insert the mammophant DNA into an egg cell – again, from an Asian elephant – that has had its DNA removed. This is the same technology used for cloning.

In 1996, Dolly the sheep became the first mammal to be cloned from an adult cell. Many different mammalian species have since been cloned, but the elephant is not among them. Cloning research suggests that, just because it is possible to clone one type of animal, it is not necessarily easy to clone another, even if they belong to closely-related species.

One key problem is that there is still a lot we do not understand about cloning. During the process, the egg somehow reprograms the newly-inserted DNA to a more youthful state so that it can drive embryonic development. It is a bit like restoring the factory settings on a mobile phone, but no one knows how it happens or how to fully control it. So in order to make a mammophant embryo, Church's team will also need to advance the science of cloning.

It is a mammoth task (sorry about that) but it is not impossible. However, even if Church pulls it off, he will still need to find a way to nourish the embryo while it grows.

Asian elephants (Elephas maximus) are endangered (Credit: Bernard Castelein/naturepl.com)

When I first heard about attempts to bring back the woolly mammoth, I was not keen. There was an elephant in the room, which most people either failed to notice or chose to ignore: in order to revive the woolly mammoth, scientists would have to perform experiments on elephants.

These are not animals to be experimented with

First, elephant eggs would be needed for the cloning process. Then, surrogate elephant mothers would be required to nurture the developing embryos in their wombs, then give birth to them and bring them up. Since cloning is an inexact science that produces far more failures than live births, this would put the health of the elephant surrogate at risk.

The trouble is that there are so few elephants left. The number of Asian elephants has more than halved over the last three generations because of habitat loss and poaching, and they are classed as "endangered".

In short, these are not animals to be experimented with. I am not keen on bringing back the woolly mammoth at the expense of an animal so deserving of our care.

However, Church is unfazed. He believes he can perform his experiments without risking any elephants at all.

Could an Asian elephant give birth to a mammoth? (Credit: Bernard Castelein/naturepl.com)

The elephant eggs needed for cloning need not come from the reproductive systems of living elephants. There are other ways to make them.

Animal studies have shown that skin cells can be reprogrammed in a dish to make stem cells, which can then be coaxed to form eggs. It is almost like cellular alchemy. Rather than performing invasive surgery to retrieve eggs from adult female elephants, it should be possible to make them from non-invasive skin biopsies.

The technology of artificial wombs is still, well, embryonic

Once the embryos have been made, they could be nurtured, not in adult animals, but in "artificial wombs". This may sound like the stuff of science fiction, but Church and other researchers are quietly developing the science needed to make it happen. He explained last week that researchers in his lab have grown a mouse embryo in an artificial womb for 10 days; halfway through its normal gestation period.

In theory, artificial wombs would get around the surrogate mother problem. But it will be no mean feat to scale them up from mice to mammoths.

Mouse pregnancies last for 20 days, while mammoth ones take over two years. And while a newborn mouse weighs as much as a paperclip, a newborn mammoth calf is the size of a washing machine. What's more, each species will need a different cocktail of "ingredients" to help its embryo grow.

In short, the technology of artificial wombs is still, well, embryonic.

At this point it should be clear that de-extinction is profoundly difficult, and that we are not going to have any living mammoths roaming the Siberian tundra in the next few years. But at the same time, it seems likely that if scientists like Church keep pushing, they will get there eventually.

The bigger question is: should we do it? What would be the point?

Siberia's ecosystem has changed over the millennia (Credit: Eric Baccega/naturepl.com)

Advocates of de-extinction will tell you there are many reasons to bring extinct species back to life.

We live in the midst of a global biodiversity crisis, with up to 150 species disappearing every day. Extinction rates are currently 1,000 times higher than during pre-human times. We are responsible for this travesty. So if the tools exist to undo some of that damage, maybe we have a moral obligation to do just that.

De-extinction should be about producing populations of genetically-diverse animals that can breed and live in the wild

However, I think we need to think a little more deeply about it.

In 2014, ecologist John Ewen of the Institute of Zoology in London, UK helped design a checklist. The idea was to help researchers select the most suitable candidates for de-extinction. The paper went on to influence a set of de-extinction guidelines drawn up by the International Union for Conservation of Nature (IUCN).

The checklist essentially asks whether, if we re-created an extinct species, it could survive in our modern world. Among other things, it asks: whether there is suitable habitat to be had; if the original cause of extinction is still present; whether the animal could become a pest; and how its revival might affect people living nearby.

"Resurrecting the woolly mammoth should be more than the production of a biological orphan destined for an exhibit," says Ewen. "To embrace this technology with responsibility, we should consider the loftier goals of ecological enrichment, and assess the feasibility and risks surrounding mammoth reintroduction."

In other words, de-extinction should be about producing populations of genetically-diverse animals that can breed and live in the wild, where they can contribute to the ecosystem.

Siberia is not all ice and snow (Credit: Konstantin Mikhailov/naturepl.com)

All living things provide vital services to the ecosystems they are part of. There are pollinators, seed dispersers, water purifiers, pest controllers, and much else.

An estimated 500 gigatonnes of organic carbon is locked up in the Arctic permafrost

Mammoths were gardeners. In their heyday, they trundled around eating grass, trampling saplings, and fertilising the ground with their nutrient-rich dung. When they went extinct, there was no other species to do these jobs. As a result, the rich "Mammoth steppe" turned to scraggy, mossy tundra.

If we were to plug the ecological niche left vacant by mammoths' demise, it may be that they could return the unproductive wastelands of northern Siberia to their biodiverse heyday. But no one knows for sure.

"There will be uncertainty here," says Ewen. "We need to judge the capacity for the mammoth to restore such habitat."

Similarly, Church argues that mammoths could help stop dangerous climate change.

Partially-frozen tundra in Siberia (Credit: Sergey Gorshkov/naturepl.com)

A series of as-yet-unpublished experiments in Siberia have suggested that, where large grazers are present, soil temperatures are several degrees colder than where they are absent.

It would still take well over half a century to make a single viable herd

"When big animals graze, they trample the snow, which exposes the surface of the soil to cold air," says biologist Sergey Zimov of theNortheast Science Station in Cherskii, Russia, who conducted the research. "This helps keep the ground frozen."

An estimated 500 gigatonnes of organic carbon is locked up in the Arctic permafrost. That is two to three times as much as in all the existing rainforests combined. As our climate changes and the Arctic melts, scientists have warned that this "carbon time bomb" could go off and accelerate global warming still further.

However, if we were to repopulate the wilds of Siberia with herds of woolly mammoth, the argument goes, they might prevent the carbon time bomb from going boom.

It is an enticing argument, but not without flaws.

Artist's impression of woolly mammoths (Mammuthus primigenius) (Credit: Stocktrek Images Inc/Alamy)

Suppose Church perfects all the methods that he needs and makes a viable hybrid "mammoth" embryo in the timescale he imagines. It would then take a further two years for that embryo to turn into a calf, and another 15 years for it to reach sexual maturity. Even if all the technical hurdles involved in making a mammoth were overcome tomorrow, it would still take well over half a century to make a single viable herd, which would not be anywhere enough to do the job.

There appear [to be] some uncertainties that may reduce the value of the mammoth as a de-extinction candidate

Instead, by that time, if current predictions are to be believed, the Arctic permafrost will already have melted. What's more, the Siberian ecosystem may have changed too much and may be unable to support the new arrivals.

In other words, we cannot look to mammoths to help solve global warming. The real story is that climate change undoubtedly played a role in polishing mammoths off last time round: they died out when Earth's climate warmed and the ice retreated. So if anything, climate change makes the future of any de-extinct mammoth looks decidedly woolly.

"Using the IUCN reintroduction criteria, there appear [to be] some uncertainties that may reduce the value of the mammoth as a de-extinction candidate," says Ewen.

At this point, it may seem that bringing back woolly mammoths is a hopeless prospect. The challenges are certainly formidable. But that is not to say that de-extinction is without value.

A kākāpō (Strigops habroptilus) (Credit: Brent Stephenson/naturepl.com)

For me, the single biggest argument in favour of resurrecting extinct species is the beneficial spin-offs it will create for endangered living species.

Conservationists plan to use genome editing and cloning to help save black-footed ferrets

The same techniques being used to bring back extinct animals – stem cell technology, genome sequencing and editing, and assisted reproduction techniques such as cloning – can be used, far more easily, on threatened living species.

In New Zealand, genome sequencing is being used to help rescue thekākāpō; a large, green, flightless parrot. The species is suffering from fertility problems and inbreeding. Researchers are currently decoding the full genetic codes of all 154 living kākāpōs, and plan to use the information to help steer their breeding program. By mating only the most genetically distinct birds, they hope to produce offspring that are more healthy and fertile.

Similar plans are also afoot in North America.

A black-footed ferret (Mustela nigripes) (Credit: Roland Seitre/naturepl.com)

Conservationists plan to use genome editing and cloning to help save black-footed ferrets. In the 1980s, these feisty little creatures were on the brink of extinction, partly because of an infectious disease called sylvatic plague. A decades-long captive breeding program has kept the species going, but there are still only a few hundred in the wild.

Worse, today's wild black-footed ferrets are massively inbred. They are all effectively second cousins. This is not good for the long-term health of the species.

If both of these projects pan out, they would make conservation history

However, stored away in vats of liquid nitrogen are the frozen cells of wild ferrets that were captured, but then died without passing on their genes. These cells are a resource waiting to be used.

In 2015, the pro-de-extinction organisation Revive and Restoresubmitted two ground-breaking proposals to the US Fish and Wildlife Service, the body that oversees American nature.

The first is to use the frozen cells to make new, genetically vibrant animals. These will then be able to breed naturally, giving the population back some of its lost genetic variation.

But there is no point going to all this trouble if the animals are then set free and become infected with plague. So the second proposal seeks to edit the ferret's genome to make it plague-resistant.

If both of these projects pan out, they would make conservation history. Even better, similar techniques could then be applied to countless other species.

One of the last northern white rhinos (Ceratotherium simum cottoni) (Credit: Ann & Steve Toon/naturepl.com)

In Kenya, the Ol Pejeta Conservancy is home to the world's last three northern white rhinos. These magnificent beasts were once widespread in east and central Africa before poaching, civil war and habitat loss took their toll.

We do not know if projects like this will work. But desperate times call for desperate measures

The last three – Sudan, Najin and Fatu – are grandfather, mother and daughter. They are too old, too ill and too closely-related to ever breed naturally. Their subspecies is functionally extinct and they are the walking dead.

However, stem cell technology and assisted reproduction could even now pull them back from the brink. Led by veterinarian Thomas Hildebrandt of the Leibniz Institute for Zoo and Wildlife Research in Berlin, Germany, researchers plan to create some truly special test-tube babies.

Using sperm from male northern white rhinos, collected and stored before they died, and eggs created by the same method that Church is developing for his mammoths, the team hope to create the embryos of northern white rhinos in a dish. These will then be transferred into the surrogate wombs of the animal's closest living relative, the southern white rhino, who will carry the little embryos to term.

We do not know if projects like this will work. But desperate times call for desperate measures.

Woolly mammoths have been extinct for thousands of years (Credit: Mim Friday/Alamy)

The world is warming, habitats are being lost, many places are becoming more polluted, and the biodiversity crisis is deepening. De-extinction, for all its pitfalls, is worthy of our attention because of the potential it has to help repair ailing ecosystems.

De-extinction is not just about bringing back the dead

In short, this is a bigger issue than simply whether we could, or should, bring back woolly mammoths. They are only one species, and there are many we could restore – whether already extinct, or merely close to it.

When de-extinct animals finally blossom into healthy wild populations, they could vastly boost overall levels of biodiversity, not just by their presence, but by the impact they will have on the other species in their ecosystems.

What's more, the knowledge we are gaining from figuring out how to bring back extinct species is already having a positive effect on the wildlife that we still have. In other words, de-extinction is not just about bringing back the dead. It is also about helping the living.

Helen Pilcher (@HelenPilcher1) is a freelance science writer. Her book Bring Back the King: The new science of de-extinction was published in 2016 by Bloomsbury.

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