How close to Earth's core can organisms live?

We don't to know much about organisms living deep below the Earth's crust. Recently a team led by S. Giovanni discovered some microbes 300 m below the ocean floor. The microbes were found to be a completley new and exotic species and apparently they feed off hydrocarbons like methane and benzene. Scientists speculate that life may exist in our Solar System far below the surface of some planets or moons. This raises some questions:

  1. What is the theoretical minimum distance from Earth's core where life can still exist. Please explain how you came up with this number. For example, there are temperature-imposed limits on many biochemical processes.

  2. Is there the potential to discover some truly alien life forms in the Earth's mantle (by this I mean, life which is not carbon based, or life which gets its energy in ways we have not seen before, or non DNA-based life, or something along these lines)?

  3. What is the greatest distance below the Earth's crust that life has been discovered? I believe it is the 300 m I cited above, but I am not 100% sure.

There's a lot we don't know about life in deep caves, but we can bound the deepest living organism to at least 3.5 kilometers down, and probably not more than 30 kilometers down.

The worms recovered from deep mining boreholes are not particularly specifically adapted to live that far down: they have similar oxygen/temperature requirements as surface nematodes.

The Tau Tona mine is about 3.5 kilometers deep and about 60˚ C at the bottom. Hydrothermal vent life does just fine up to about 80˚C, and the crust gets warmer at "about" 25˚C per kilometer. It's entirely reasonable to expect life to about 5 kilometers down, but further than that is speculation.

Increasing pressure helps to stabilize biological molecules that would otherwise disintegrate at those temperatures, so it's not impossible there could be life even deeper. It may even be likely, given that the Tau Tona life breathes oxygen.

I am certain no life we might recognize as life exists in the upper mantle.

At least 283 bacterial species (as of June, 2017) have been found in deep mines, deep seas, or deep-sea sediments; for example:

Abyssivirga alkaniphila, 2.3 km; Alcanivorax dieselolei, 5.0 km; Alcanivorax marinus, 2.5 km; Alcanivorax nanhaiticus, 2.1 km; Alkalimonas collagenimarina, 4.0 km; Alkaliphilus transvaalensis, 3.2 km; Altererythrobacter atlanticus, 2.6 km; Altererythrobacter marinus, 1.5 km; Amycolatopsis albispora, 2.9 km; Anoxybacter fermentans, 2.9 km; Arthrobacter ardleyensis, 5.0 km; Aurantivirga profunda, 1.0 km; Arthrobacter subterraneus, 0.5 km.

For links to the articles describing these bacterial species, see:

Life Thrives Within the Earth&rsquos Crust

Catherine Offord
Oct 1, 2018

A bout a 20-minute drive north of the industrial town of Timmins, Ontario, the ground gives way to a gaping pit stretching more than 100 meters across. This pit is the most recognizable feature of Kidd Creek Mine, the deepest copper and zinc mine in the world. Below the Earth’s surface, a maze of underground tunnels and shafts pierces 3 kilometers of ancient volcanic rock. Were it not for a huge ventilation system keeping the passages cool, the air temperature at this depth would be 34 °C (93 °F).

It’s here that Barbara Sherwood Lollar, a hydrogeologist at the University of Toronto, journeys into the planet’s crust to hunt for signs of life. “You get into a small truck or vehicle and go down a long, winding roadway that corkscrews down into the Earth,” she tells The Scientist. By the time she and her fellow passengers clamber out into the corridors at the end of the roadway, “we are literally walking along what was the ocean floor 2.7 billion years ago,” she says. “It’s an utterly fascinating and magical place to visit.”

Unlike miners, who navigate these tunnels in search of metal ores, Sherwood Lollar and her colleagues are on the lookout for pools of salty water. “These aren’t waters you’d pump into your cottage and drink or spread on your crops,” Sherwood Lollar says. “These are waters that have been in contact with the rock for long geochemical timescales—they’re full of dissolved cations and anions that they’ve leached out of the minerals.” So full, in fact, that they give off a distinctive, musty odor. “As we’re walking along these tunnels, if I get a whiff of that stenchy smell, then we head in that direction.”

Where there’s water, there’s the potential for life. In 2006, Sherwood Lollar was part of a team led by Tullis Onstott at Princeton University that discovered an anaerobic, sulfate-reducing bacterium thriving in the sulfate-rich fracture waters of Mponeng gold mine in South Africa, 2.8 kilometers underground. 1 A few years later, a different group described a diverse microbial community living at a similar depth in the Earth’s crust, accessed via a borehole drilled into the ground in Finland. 2 With the recent discovery of 2-billion-year-old, hydrogen- and sulfate-rich water seeping out of the rock in Kidd Mine, Sherwood Lollar and her colleagues are hoping they might again find life. 3

Before the rise of the land plants, deep biomass could have outweighed life on the surface by an order of magnitude.

These expeditions are just one part of a rapidly expanding field of research focused on documenting microbial and even eukaryotic life dwelling hundreds of meters deep in the Earth’s crust—the vast sheath of rock encasing the planet’s mantle. Researchers are now exploring this living underworld, or deep biosphere, not only in the ancient, slow-changing continental crust beneath our feet, but in the thinner, more dynamic oceanic crust under the seafloor. (See illustration on page 32.) Such habitats have become more accessible thanks to the last two decades’ expansion of scientific drilling projects—whereby researchers haul up cores of rock to study on the surface—as well as a growing number of expeditions into the Earth via mines or cracks in the ocean floor.

Studies of these dark—and often anoxic and hot—environments are challenging scientists to rethink the limits of life, at the same time highlighting how little we know about the world beneath our feet. “It’s a really good field if you don’t mind not knowing all the answers,” says Jason Sylvan, a geomicrobiologist at Texas A&M University. “For some people, that freaks them out. For me, a field is more exciting when you can ask really big questions.”

Importance in Research

The enzymes secreted by extremophiles, termed “extremozymes,” that allow them to function in such forbidding environments are of great interest to medical and biotechnical researchers. Perhaps they will be the key to creating genetically based medications, or creating technologies that can function under extreme conditions.

Of course, different environmental conditions require different adaptations by the organisms that live those conditions. Extremophiles are classified according to the conditions under which they grow. Usually, however, environments are a mix of different physiochemical conditions, requiring extremophiles to adapt to multiple physiochemical parameters. Extremophiles found in such conditions are termed “polyextremophiles.”


Acidophiles are adapted to conditions with acidic pH values that range from 1 to 5. This group includes some eukaryotes, bacteria, and archaea that are found in places like sulfuric pools, areas polluted by acidic mine drainage, and even our own stomachs!

Acidophiles regulate their pH levels through a variety of specialized mechanisms— some of which are passive (not exerting energy), and some of which are active (exerting energy). Passive mechanisms usually involve reinforcing the cell membrane against the external environment, and may involve secreting a biofilm to hinder the diffusion of molecules into the cell, or changing their cell membrane entirely to incorporate protective substances and fatty acids. Some acidophiles can secrete buffer molecules to help raise their internal pH levels. Active pH regulation mechanisms involve a hydrogen ion pump that expels hydrogen ions from the cell at a constantly high rate.


Alkaliphiles are adapted to conditions with basic pH values of 9 or higher. They maintain homeostasis by both passive and active mechanisms. Passive mechanisms include pooling cytoplasmic polyamines inside the cell. The polyamines are rich with positively charged amino groups that buffer the cytoplasm in alkaline environments. Another passive mechanism is having a low membrane permeability, which hinders the movement of protons in and out of the cell. The active method of regulation involves a sodium ion channel that carries protons into the cell.


Thermophiles thrive in extremely high temperatures between 113 and 251 degrees Fahrenheit. They can be found in places like hydrothermal vents, volcanic sediments, and hot springs. Their survival in such places can be accredited to their extremozymes. The amino acids of these types of enzymes do not lose their shape and misfold in extreme heat, allowing for continued proper function.


Psychrophiles (also known as Cryophiles) thrive in extremely low temperatures of 5 degrees Fahrenheit or lower. This group belongs to all three domains of life (bacteria, archaea, and eukarya), and they can be found in places like cold soils, permafrost, polar ice, cold ocean water, and alpine snow packs.

One way they survive in extreme cold can be attributed to their extremozymes, which continue to function at low temperatures, and a little more slowly at even lower temperatures. Psychrophiles are also able to produce proteins that are functional in cold temperatures, and contain large amounts of unsaturated fatty acids in their plasma membranes that help buffer the cells from the cold. Most notably, however, some psychrophiles are able to replace the water in their bodies with the sugar trehalose, preventing the formation of harmful ice-crystals.


Xerophiles grow in extremely dry conditions which can be very hot or very cold. They have been found in places like the Atacama Desert, the Great Basin, and the Antarctic. Like their psychrophilic friends, some xerophiles have the ability to replace water with trehalose, which can also protect membranes and other structures from periods with low water availability.

Barophile (Piezophile)

Barophiles are organisms that grow best under high pressures of 400 atm or more. They can survive by regulating the fluidity of the phospholipids in the membrane. This fluidity compensates for the pressure gradient between the inside and outside of the cell, and the external environment. Extreme barophiles grow optimally at 700 atm or higher, and will not grow at lower pressures.


Halophiles are organisms that require high salt concentrations for growth. At salinities exceeding 1.5M, prokaryotic bacteria are predominant. Still, this group belongs to all three domains of life, but in smaller numbers.

Overcoming the challenges of hypersaline environments starts with minimizing cellular water loss. Halophiles do this by accumulating solutes in the cytoplasm via varying mechanisms. Halophilic archaea use a sodium-potassium ion pump to expel sodium and intake potassium. Halotolerant bacteria balance the osmotic pressure by using glycerol as compatible solutes.

How we know what lies at Earth's core

Humans have been all over the Earth. We've conquered the lands, flown through the air and dived to the deepest trenches in the ocean. We've even been to the Moon. But we've never been to the planet's core.

We haven't even come close. The central point of the Earth is over 6,000km down, and even the outermost part of the core is nearly 3,000 km below our feet. The deepest hole we've ever created on the surface is the Kola Superdeep Borehole in Russia, and it only goes down a pitiful 12.3 km.

All the familiar events on Earth also happen close to the surface. The lava that spews from volcanoes first melts just a few hundred kilometres down. Even diamonds, which need extreme heat and pressure to form, originate in rocks less than 500km deep.

What's down below all that is shrouded in mystery. It seems unfathomable. And yet, we know a surprising amount about the core. We even have some idea about how it formed billions of years ago &ndash all without a single physical sample. This is how the core was revealed.

One good way to start is to think about the mass of the Earth, says Simon Redfern of the University of Cambridge in the UK.

Most of the Earth's mass must be located towards the centre of the planet

We can estimate Earth's mass by observing the effect of the planet's gravity on objects at the surface. It turns out that the mass of the Earth is 5.9 sextillion tonnes: that's 59 followed by 20 zeroes.

There's no sign of anything that massive at the surface.

"The density of the material at the Earth's surface is much lower than the average density of the whole Earth, so that tells us there's something much denser," says Redfern. "That's the first thing."

Essentially, most of the Earth's mass must be located towards the centre of the planet. The next step is to ask which heavy materials make up the core.

The answer here is that it's almost certainly made mostly of iron. The core is thought to be around 80% iron, though the exact figure is up for debate.

An iron core would account for all that missing mass

The main evidence for this is the huge amount of iron in the universe around us. It is one of the ten most common elements in our galaxy, and is frequently found in meteorites.

Given how much there is of it, iron is much less common at the surface of the Earth than we might expect. So the theory is that when Earth formed 4.5 billion years ago, a lot of iron worked its way down to the core.

That's where most of the mass is, and it's where most of the iron must be too. Iron is a relatively dense element under normal conditions, and under the extreme pressure at the Earth's core it would be crushed to an even higher density, so an iron core would account for all that missing mass.

But wait a minute. How did that iron get down there in the first place?

The iron must have somehow gravitated &ndash literally &ndash towards the centre of the Earth. But it's not immediately obvious how.

Most of the rest of the Earth is made up of rocks called silicates, and molten iron struggles to travel through them. Rather like how water on a greasy surface forms droplets, the iron clings to itself in little reservoirs, refusing to spread out and flow.

The pressure actually changes the properties of how iron interacts with the silicate

A possible solution was discovered in 2013 by Wendy Mao of Stanford University in California and her colleagues. They wondered what happened when the iron and silicate were both exposed to extreme pressure, as happens deep in the earth.

By pinching both substances extremely tightly using diamonds, they were able to force molten iron through silicate.

"The pressure actually changes the properties of how iron interacts with the silicate," says Mao. "At higher pressures a 'melt network' is formed."

This suggests the iron was gradually squeezed down through the rocks of the Earth over millions of years, until it reached the core.

At this point you might be wondering how we know the size of the core. What makes scientists think it begins 3000km down? There's a one-word answer: seismology.

All the seismic stations dotted all over the Earth recorded the arrival of the tremors

When an earthquake happens, it sends shockwaves throughout the planet. Seismologists record these vibrations. It's as if we hit one side of the planet with a gigantic hammer, and listened on the other side for the noise.

"There was a Chilean earthquake in the 1960s that generated a huge amount of data," says Redfern. "All the seismic stations dotted all over the Earth recorded the arrival of the tremors from that earthquake."

Depending on the route those vibrations take, they pass through different bits of the Earth, and this affects how they "sound" at the other end.

Early in the history of seismology, it was realised that some vibrations were going missing. These "S-waves" were expected to show up on one side of the Earth after originating on the other, but there was no sign of them.

It turned out that rocks became liquid around 3000km down

The reason for this was simple. S-waves can only reverberate through solid material, and can't make it through liquid.

They must have come up against something molten in the centre of the Earth. By mapping the S-waves' paths, it turned out that rocks became liquid around 3000km down.

That suggested the entire core was molten. But seismology had another surprise in store.

In the 1930s, a Danish seismologist named Inge Lehmann noticed that another kind of waves, called P-waves, unexpectedly travelled through the core and could be detected on the other side of the planet.

P-waves really were travelling through the core

She came up with a surprising explanation: the core is divided into two layers. The "inner" core, which begins around 5,000km down, was actually solid. It was only the "outer" core above it that was molten.

Lehmann's idea was eventually confirmed in 1970, when more sensitive seismographs found that P-waves really were travelling through the core and, in some cases, being deflected off it at angles. Sure enough, they still ended up on the other side of the planet.

It's not just earthquakes that sent useful shockwaves through the Earth. In fact, seismology owes a lot of its success to the development of nuclear weapons.

A nuclear detonation also creates waves in the ground, so nations use seismology to listen out for weapons tests. During the Cold War this was seen as hugely important, so seismologists like Lehmann got a lot of encouragement.

This turns out to be quite tricky to determine

Rival countries found out about each other's nuclear capabilities and along the way we learned more and more about the core of the Earth. Seismology is still used to detect nuclear detonations today.

We can now draw a rough picture of the Earth's structure. There is a molten outer core, which begins roughly halfway to the planet's centre, and within it is the solid inner core with a diameter of 1,220 km.

But there is a lot more to try and tease out, especially about the inner core. For starters, how hot is it?

This turns out to be quite tricky to determine, and baffled scientists until quite recently, says Lidunka Vočadlo of University College London in the UK. We can't put a thermometer down there, so the only solution is to create the correct crushing pressure in the lab.

Earth's core has stayed warm thanks to heat retained from the formation of the planet

In 2013 a team of French researchers produced the best estimate to date. They subjected pure iron to pressures a little over half that at the core, and extrapolated from there. They concluded that the melting point of pure iron at core temperatures is around 6,230 °C. The presence of other materials would bring the core's melting point down a bit, to around 6,000 °C. But that's still as hot as the surface of the Sun.

A bit like a toasty jacket potato, Earth's core has stayed warm thanks to heat retained from the formation of the planet. It also gets heat from friction as denser materials shift around, as well as from the decay of radioactive elements. Still, it is cooling by about 100 °C every billion years.

Knowing the temperature is useful, because it affects the speed at which vibrations travel through the core. That is handy, because there is something odd about the vibrations.

P-waves travel unexpectedly slowly as they go through the inner core &ndash slower than they would if it was made of pure iron.

It's a Cinderella problem: no shoe will quite fit

"Wave velocities that the seismologists measure in earthquakes and whatnot are significantly lower [than] anything that we measure in an experiment or calculate on a computer," says Vočadlo. "Nobody as yet knows why that is."

That suggests there is another material in the mix.

It could well be another metal, called nickel. But scientists have estimated how seismic waves would travel through an iron-nickel alloy, and it doesn't quite fit the readings either.

Vočadlo and her colleagues are now considering whether there might be other elements down there too, like sulphur and silicon. So far, no-one has been able to come up with a theory for the inner core's composition that satisfies everyone. It's a Cinderella problem: no shoe will quite fit.

That could explain why the seismic waves pass through more slowly than expected

Vočadlo is trying to simulate the materials of the inner core on a computer. She hopes to find a combination of materials, temperatures and pressures that would slow down the seismic waves by the right amount.

She says the secret might lie in the fact that the inner core is nearly at its melting point. As a result, the precise properties of the materials might be different from what they would be if they were safely solid.

That could explain why the seismic waves pass through more slowly than expected.

"If that's the real effect, we would be able to reconcile the mineral physics results with the seismological results," says Vocadlo. "People have not been able to do that yet."

There are plenty of riddles about the earth's core still to solve. But without ever digging to those impossible depths, scientists have figured out a great deal about what is happening thousands of kilometres beneath us.

The magnetic field helps to shield us from harmful solar radiation

Those hidden processes in the depths of the Earth are crucial to our daily lives, in a way many of us don't realise.

Earth has a powerful magnetic field, and that is all thanks to the partially molten core. The constant movement of molten iron creates an electrical current inside the planet, and that in turn generates a magnetic field that reaches far out into space.

The magnetic field helps to shield us from harmful solar radiation. If the core of the Earth wasn't the way it is, there would be no magnetic field, and we would have all sorts of problems to contend with.

None of us will ever set eyes on the core, but it's good to know it's there.

Curious Kids: what would happen if the Earth’s core went cold?

Paula Koelemeijer receives funding from the Royal Society and University College Oxford.


University College London provides funding as a founding partner of The Conversation UK.

The Conversation UK receives funding from these organisations

Curious Kids is a series for children of all ages, where The Conversation asks experts to answer questions from kids. All questions are welcome: find out how to enter at the bottom of this article.

What would happen if the Earth’s core was no longer molten hot? – Amelia, age 13, Devon, UK

Thanks Amelia, that’s a very good question! The Earth’s core is cooling down very slowly over time. One day, when the core has completely cooled and become solid, it will have a huge impact on the whole planet. Scientists think that when that happens, Earth might be a bit like Mars, with a very thin atmosphere and no more volcanoes or earthquakes. Then it would be very difficult for life to survive – but that won’t be a problem for several billions of years.

Right now, the Earth’s core is not entirely molten. The inner core is a sphere of solid iron, while the outer core is made of molten iron thousands of kilometres thick.

Scientists know this because the shock waves made by earthquakes can be recorded on the other side of the Earth – and we would not expect to see them there if the inner core was also molten.

The whole core was molten back when the Earth was first formed, about 4.5 billion years ago. Since then, the Earth has gradually been cooling down, losing its heat to space. As it cooled, the solid inner core formed, and it’s been growing in size ever since.

But this process is very slow: the inner core only grows about one millimetre a year, because the Earth has a rocky mantle in between its hot core and its cold surface, which stops it from cooling down too quickly – just like your coat keeps you warm in winter.

The slow cooling of our planet causes the molten iron in the outer core to flow and swirl fast as heat is transported to the mantle, and this gives Earth its magnetic field. The magnetic field is like a magnet that acts at a distance, and even though we cannot see it with our eyes, it does lots of important jobs on our planet.

The Earth’s magnetic field in action. Shutterstock.

The Earth’s magnetic field protects life on the Earth’s surface from harmful particles coming from the sun. It also keeps the planet’s atmosphere in place and helps animals to find their way around.

The heat escaping from the core also makes material move around in different layers of our planet – from the rocky mantle to the rigid plates on the surface, where you and I live.

This movement can cause the plates on the surface to rub together, which creates earthquakes and volcanoes. That’s why living in places where two plates meet – such as Nepal or Japan – can be very dangerous.

An active volcano in Guatemala. Shutterstock.

When the molten outer core cools and becomes solid, a very long time in the future, the Earth’s magnetic field will disappear.

When that happens, compasses will stop pointing north, birds will not know where to fly when they migrate, and the Earth’s atmosphere will disappear. This will make life on Earth very difficult for human beings and other life forms.

When the Earth has cooled completely, the movement in the mantle will also stop eventually. Then, the plates on the surface will no longer move and there will be fewer earthquakes and volcanic eruptions.

You might think that this would be good for people – especially those living in places like Tokyo – but volcanic eruptions also produce fertile soil for farming, and gases that make up the air that we breathe.

After all this, Earth could look a bit like Mars. On the surface of Mars, scientists have seen features that are related to volcanoes and moving plates. But they are not moving any more, and there is no magnetic field and only a thin atmosphere left.

We do not know whether the core of Mars is still molten or not, but a robot called InSight recently landed on Mars that will help us to find out!

But for now, you don’t have to worry about the Earth’s core losing all its heat and becoming solid, because the mantle is wrapped around the core, keeping it nice and warm.

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Benthos, the assemblage of organisms inhabiting the seafloor. Benthic epifauna live upon the seafloor or upon bottom objects the so-called infauna live within the sediments of the seafloor. By far the best-studied benthos are the macrobenthos, those forms larger than 1 mm (0.04 inch), which are dominated by polychaete worms, pelecypods, anthozoans, echinoderms, sponges, ascidians, and crustaceans. Meiobenthos, those organisms between 0.1 and 1 mm in size, include polychaetes, pelecypods, copepods, ostracodes, cumaceans, nematodes, turbellarians, and foraminiferans. The microbenthos, smaller than 0.1 mm, include bacteria, diatoms, ciliates, amoeba, and flagellates.

The variety and abundance of the benthos vary with latitude, depth, water temperature and salinity, locally determined conditions such as the nature of the substrate, and ecological circumstances such as predation and competition. The principal food sources for the benthos are plankton and organic debris from land. In shallow water, larger algae are important, and, where light reaches the bottom, benthic photosynthesizing diatoms are also a significant food source. Hard and sandy substrates are populated by suspension feeders such as sponges and pelecypods. Softer bottoms are dominated by deposit eaters, of which the polychaetes are the most important. Fishes, starfish, snails, cephalopods, and the larger crustaceans are important predators and scavengers.

The oldest living thing on Earth

Mayflies live a day, humans live a century, if we're lucky, but what is the oldest living organism on the planet? For scientists, accurately proving the age of any long-lived species is a hard task.

Under the boughs of a 300-year-old sweet chestnut tree in the Royal Botanic Gardens in Kew, Tony Kirkham, head of the arboretum, confirms that trees are capable of outliving animals.

Proving this can involve some traditional detective work, as he explains: "First of all we can look at previous records, to find out if a tree was growing there at a set date. Then we look at paintings and artwork, to look to see if that tree was present. And old Ordnance Survey maps quite clearly show ancient trees, especially important ones."

A well-known way of measuring the age of a tree is by counting the rings in its trunk: one ring per year of growth. It's a process known as dendrochronology and only works for certain types of tree that have an annual growth spurt.

The obvious problem is that counting rings normally involves cutting down the tree.

Arboriculturalists get around this by using an increment borer, a drill that allows them to take out a core, and count the rings without fatally damaging the tree.

It's a delicate art, and, Tony says, back in the 1960s, one scientist's drill broke off inside the bristlecone pine tree he was sampling.

The kit is expensive, and to help him recover the lost instrument, a forester helpfully cut down the tree. Once felled, the tree could be easily aged, and was found to be 5000 years old.

"It was terrible but so much science came out of that opportunity, and since then, we've found trees that are as old, if not older," admits Tony.

A team of researchers in the US keeps a list, called the Old List, of officially dated ancient trees.

They've found a sacred fig tree in Sri Lanka that is at least 2,222 years old.

There's a Patagonian cypress tree in Chile which, at 3,627 years old, is as old as Stonehenge.

A Great Basin bristlecone pine in California's White Mountains named Methuselah comes in at 4,850 years old. But the oldest tree on the list, an unnamed bristlecone pine from the same location, has a core suggesting it is 5,067 years old.

This time-worn tree has lived through the rise and fall of the Roman Empire. It was already established when the Ancient Egyptians started building pyramids.

We investigated the bristlecone pine tree after William Adams from London asked us: "What's the oldest tree or other living organism on Earth?" If you've got a science question you want BBC CrowdScience to look into, get in touch via the form below.

If you are reading this page on the BBC News app, you will need to visit the mobile version of the BBC website to submit your question.

Is this 5,000-year-old Great Basin bristlecone pine the oldest single living thing on the planet? That depends on your definition of a "single tree".

In Fishlake National Park in Utah in the US lives a quaking aspen tree that most people would struggle to see as "a tree".

It's a clonal tree called "Pando", from the Latin meaning "I spread", and for good reason.

It is so large that it is easy to mistake for a forest. However, Pando, despite being the size of Vatican City, has all sprung from one seed, and, over the years, has grown a single vast rootstock supporting an estimated 50,000 tree trunks. Accurately estimating how many years is problematic, says population geneticist Prof Karen Mock from Utah State University, who works on the aspen.

"There have been all kinds of different estimates but the original tree is almost certainly not there," he told the BBC.

Clonal trees grow in all directions and regenerate themselves as they go. This means taking a core from a trunk will not give you the age of the whole tree.

Scientists try to get around this problem by equating size to age. It's an inaccurate process and Pando's estimated age ranges from a few thousand to 80,000 years old.

Prof Mock hopes that a new technique, looking at how many DNA mutations are accumulated over time, could give them another way of assessing the age of this remarkable tree.

Physical and Chemical Features

Light and temperature are two key physical features of lakes and ponds. Light from the sun is absorbed, scattered, and reflected as it passes through Earth's atmosphere, the water's surface, and the water. The quantity and quality of light reaching the surface of a lake or pond depends on a variety of factors, including time of day, season, latitude, and weather. The quality and quantity of light passing through lake or pond water is affected by properties of the water, including the amount of particulates (such as algae) and the concentration of dissolved compounds. (For example, dissolved organic carbon controls how far ultraviolet wavelengths of light penetrate into the water.)

Light and wind combine to affect water temperature in lakes and ponds. Most lakes undergo a process called thermal stratification, which creates three distinct zones of water temperature. In summer, the water in the shallowest layer (called the epilimnion) is warm, whereas the water in the deepest layer (called the hypolimnion) is cold. The middle layer, the metalimnion, is a region of rapid temperature change. In winter, the pattern of thermal stratification is reversed such that the epilimnion is colder than the hypolimnion. In many lakes, thermal stratification breaks down each fall and spring when rapidly changing air temperatures and wind cause mixing. However, not all lakes follow this general pattern. Some lakes mix only once a year and others mix continuously.

The chemistry of lakes and ponds is controlled by a combination of physical, geological, and biological processes. The key chemical characteristics of lakes and ponds are dissolved oxygen concentration, nutrient concentration, and pH . In lakes and ponds, sources of oxygen include diffusion at the water surface, mixing of oxygen-rich surface waters to deeper depths, and photosynthesis. Oxygen is lost from lakes and ponds during respiration by living organisms and because of chemical processes that bind oxygen. The two most important nutrients in lakes and ponds are nitrogen and phosphorus. The abundance of algae in most lakes and ponds is limited by phosphorus availability, whereas nitrogen and iron are the limiting nutrients in the ocean. The acidity of water, measured as pH, reflects the concentration of hydrogen ions . The pH value of most lakes and ponds falls between 4 and 9 (the pH value of distilled water is 7). Some aquatic organisms are adversely affected by low pH conditions caused by volcanic action, acid-releasing vegetation surrounding bog lakes, and acid rain.


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Environment, the complex of physical, chemical, and biotic factors that act upon an organism or an ecological community and ultimately determine its form and survival.

The Earth’s environment is treated in a number of articles. The major components of the physical environment are discussed in the articles atmosphere, climate, continental landform, hydrosphere, and ocean. The relationship between the principal systems and components of the environment, and the major ecosystems of the Earth are treated in the article biosphere. The significant environmental changes that have occurred during Earth’s history are surveyed in the article geochronology. The pollution of the environment and the conservation of its natural resources are treated in the article conservation. Hazards to life in the biosphere are discussed in the articles death, disease, and immune system.

B1.4 Interdependence and Adaptation

Organisms are well adapted to survive in their normal environment. Population size depends on a variety of factors including competition, predation, disease and human influences. Changes in the environment may affect the distribution and behaviour of organisms.

  • To survive, organisms require a supply of materials from their surroundings and from the other living organisms there.
  • Organisms live, grow and reproduce in places where, and at times when, conditions are suitable.


Animals often compete with each other for:

Plants often compete with each other for:

  • Organisms have features (adaptations) which enable them to survive in the conditions in which they normally live
  • The organisms that are best adapted to make use of their resources in a habitat are more likely to survive and increase in numbers
  • For example:
    • To be able to obtain a certain food better.
    • To make it more difficult for predators to catch them.
    • To survive in extreme climates, eg arctic or deserts
      • Plants lose water vapour from the surface of their leaves.
      • It is essential that they have adaptations which minimise this.

      Extreme adaptations:

      • Extremophiles are organisms that live in extreme environments.
      • Some may be tolerant to high levels of salt, high temperatures or high pressures.
      • Animals and plants may be adapted to cope with specific features of their environment eg thorns, poisons and warning colours to deter predators.

      Extreme Animals

      • Animals may be adapted for survival in dry and arctic environments by means of:
        • changes to surface area
        • thickness of insulating coat
        • amount of body fat
        • Examples:
          • Camel
            • The camel can go without food and water for 3 to 4 days.
            • Fat stored in their humps provides long term food reserve, and a supply of metabolic water.
            • The fat is not distributed around the body this reduces insulation, allowing more heat loss.

            They are tall and thin, increasing their surface area to volume ration, increasing heat loss by radiation.

            • Polar Bear
              • Polar bear has thick fur and fat beneath its skin to insulate it.
              • Their large, furry feet help to distribute their weight as they walk on a thin ice.
              • They are white which camouflages them against the snow. This helps them to hunt.
              • They are compact in shape, reducing their surface area to volume ratio this reduces heat loss by radiation.

              Extreme Plants

              • Plants may be adapted to survive in dry environments by means of:
                • changes to surface area, particularly of the leaves
                • water-storage tissues
                • extensive root systems.
                • Desert plants
                • Eg the cactus, require very little water to survive
                • Leaves are spines.
                • Spines guard against most browsing herbivorous animals.
                • Spines also reduce their surface area, reducing water loss by evaporation
                • A thick waxy coating surrounds the plant to reduce evaporation.
                • Fewer ‘stomata’, reducing water loss

                Roots tend to spread sideways to catch rain water.

                • Arctic plants
                • Many of the plants are small, growing close to the ground and very close together to avoid the wind and conserve heat.
                • Some possess a light, fuzzy covering to insulate the buds so they can grow.
                • Many are dark colors of blue and purple to absorb the heat from the sunlight even during the winter months.
                • Because of the cold and short growing seasons, arctic plants grow very slowly.
                • Some grow for ten years before they produce any buds for reproduction.


                • Microorganisms have adaptations that enable them to survive in different environments.
                • Slime capsule around some bacterial cell wall sticks them to surfaces and prevents them drying out.
                • Some have the ability to form spores to survive when conditions are harsh.
                • Some microorganisms have flagella which enable them to move around quickly.
                • Bacteria undergo rapid reproduction when conditions are favourable.
                • Some bacteria can survive extreme conditions:
                  • Temperatures as little as -15°C to as high as 121°C
                  • pH values 0.0 to 12.8
                  • High levels of pressure deep in the oceans
                  • High salt concentrations
                  • Very dry conditions.

                  Environmental change

                  • Changes in the environment affect the distribution of living organisms.
                  • For example, the changing distribution of some bird species and the disappearance of pollinating insects including bees.
                  • Animals and plants are subjected to environmental changes.
                  • Such changes may be caused by living or non-living factors.

                  Non-living (abiotic) factors:

                  • Food
                  • Predation
                  • Grazing
                  • Disease
                  • Competition – for: food, light, water, space.

                  Living organisms can be used as indicators of pollution:

                  • Lichens are symbiotic associations of algae and fungi species that attach to tree trunks and rock.
                  • They are sensitive to changes in air quality.
                  • They are very sensitive to sulphur dioxide (SO2) pollution in the air.
                  • This is released from industry and burning fossil fuels, especially coal.
                  • Lichens absorb sulphur dioxide dissolved in water.
                  • It destroys the chlorophyll in the algae preventing it from photosynthesising and killing the lichen.
                  • Some species only grow in non-polluted air.
                  • Some species grow in polluted air.
                  • These lichens can be used as air pollution indicators.
                  • Invertebrate animals are sensitive to changes in the concentration of dissolved oxygen in water.
                  • Oxygen concentrations decrease when pollutants are released into rivers and lakes.
                  • Some invertebrates survive in low-oxygen concentrations.
                  • Some invertebrates can only survive in higher oxygen concentrations.
                  • These invertebrate animals can be used as water pollution indicators.

                  Non-living indicators.

                  • Environmental changes can be measured using non-living indicators.
                  • For example. oxygen levels, temperature and rainfall.

                  Scientists continually monitor these factors to show trends in environmental changes

                  Watch the video: What Would a Journey to the Earths Core Be Like? (January 2022).