Habitats and ecosystems

So what is a habitat and an ecosystem?

Habitats are the places where an animal or plant lives. These species share their space with other animals and plants to form biological communities, and it’s within these communities that the food chains or food webs are formed.

Each animal or plant fills a particular niche in the community, for example, the Antarctic food web is formed around krill – they feed on phytoplankton and zooplankton, but are themselves food for animals higher up the trophic levels like penguins and whales.

An ecosystem is the all encompassing whole of the habitats, biological communities and the non-living entities like rocks, water and gases.

Trophic levels

Trophic levels refer to the place in the food webs where animals and plants sit. At the bottom of food webs are autotrophs or primary producers. These include plants on land or phytoplankton in the oceans. Through photosynthesis they harness the power of the Sun to produce their structures and generate energy to grow and reproduce.

In turn, these primary producers are food for primary consumers, which are in turn prey for secondary consumers, and so on up to even higher levels. The consumers are collectively called heterotrophs.

A simple Antarctic food chain is shown below. The arrows indicate the flow of energy from the low trophic levels to the high trophic levels.

Food chain

Ecosystems that share similar biotic and abiotic factors, like similar animals and plants, form biomes. These can include a temperate forest, the taiga or the tundra.

Biological productivity

Whenever there is a greater net primary productivity, sufficient moisture levels and a not too extreme temperature range, there is greater biodiversity.

Some factors can limit biological productivity, in the polar regions the main factors include sunlight – with such great seasonal change from dark to light, this is the most important factor, but lack of water can also be very important, especially when much of it is locked up in ice.

Living in extreme environments

Some organisms are able to withstand extreme environments. In the cold polar regions, these are called psychophriles. These are mainly bacteria, and they can survive temperatures that are consistently below -15°C. These organisms can use sulfur and iron to produce carbohydrates through the process of chemosynthesis – so they will not be reliant upon sunlight for survival.

Rocks on glaciers have higher albedos than the snow and ice around them, so they can melt the snow and ice, forming cryoconite holes. These are filled with water and can be home to tiny animals and bacteria.

Antarctic biomes

Antarctica is rightly well-known for its massive ice-caps, but it also contains other biomes.

The dry valleys form a polar desert. Snow evaporates readily because the air is so dry. They also contain wind-sculpted rocks called ventifracts. But even here life is found; lichens extract nutrients from the rocks.

In other parts of Antarctica, the tops of mountains pierce the ice sheet to form nunataks. Birds like snow and Antarctic petrels travel up to 300 miles (482 km) from the coast to nest here. The petrels are subject to less competition from penguins and other species at the coasts for valuable nesting sites, and the nunataks provide some of the rare areas of bare rock in Antarctica on which the birds can lay their eggs.

Tundra

In the Arctic, the tundra forms one of the largest biomes on Earth. Here in summer, the land is free of ice, with mean temperatures of just under 10°C. Permafrost reaches down to 400m under the ground – this is the frozen remains of vegetation that has built up year by year. The vegetation has not rotted away due to the cold temperatures and long winter period. The permafrost holds around one third of all the carbon locked up in soil on Earth.

Migration plays a big role in the tundra. The mass movements of caribou followed by wolves is a common feature on wildlife documentaries like Frozen Planet or Planet Earth.

Taiga

To the south of the tundra is the taiga. This is the world’s largest biome with around one quarter of the world’s forests. It is not a uniform forest though, to the north, the trees are widely spaced apart, but as you move south, the trees become closer packed together and in their interior it is warmer than outside the forest.

Many birds move to the taiga in summer – with around 300 species found. However, only around 30 species are found here during the winter.

The OU’s course The frozen planet’s chapter 5 looked at the adaptations that animals and plants have evolved to live in these cold, seemingly inhospitable environments. It talked about two categories of animals:

• endotherms – these are animals, like mammals and birds, that can regulate their own temperature
• ectotherms – this includes insects that use external sources to generate heat

Endotherms

The endotherms show many adaptations, including:

• shivering – generates heat as a by-product of the movement, although in some animals this can use up energy when they would be better preserving it, for example, when food is scarce
• hibernation – temperature and breathing rates are lowered, reducing energy expenditure. Polar bears do not hibernate, instead they go into a period of dormancy where they are inactive for a few days at a time. If you’ve read about the “outraged fury” about the Frozen Planet filming young polar bears in a “den” in an animal park, then just thinking that the bears don’t go into full hibernation is a big reason not to approach them in the wild
• huddling together – most apparent in animals like elephant seals and Emperor penguins, this reduces the area of their bodies that is exposed to the elements
• hair/fur – long hair or fut traps heat close to the body providing an insulation layer. Wind chill is caused by warm air that has been radiated from our bodies being blown away by the wind, and so long fur can help reduce this effect. Some animals, like the polar bear and Arctic fox, have transparent, hollow hair that scatters light, making them appear white.
• feathers – some birds, like the penguins, have stiff feathers that perform a similar role as fur described above, underneath these stiff feathers they have downy feathers providing even more insulation
• subcutaneous fat – heat travels slowly through it, so this means less heat is lost
• countercurrent heat exchange – this keeps heat within the body, feet can be cold but does not affect animal
• surface area to volume ratio – a smaller ratio means less heat is lost, so larger bodies in polar animals is a beneficial adaptation

Ectotherms

Ectotherms have their own cold adaptations:

• some fish have no ice-forming nuclei in their blood, so can survive as “supercooled” in water close to the freezing point
• antifreeze – proteins get absorbed onto ice crystals, preventing them growing
• absence of haemoglobin or myoglobin reduces viscosity of blood, so it becomes easier to pump around the body. Normally low temperatures would increase viscosity making it more difficult to pump the blood around the body
• able to exploit high oxygen concentration of polar waters

Plant adaptations

Plants also show adaptations to the polar environments:

• they grow close to the ground in a cushion, this creates a microclimate of 10°C warmer than surrounding air
• leaves small and chunky – reduces evaporation of because of smaller surface area
• some flowers are able to track the Sun around the sky during the short summers when the Sun does not set

Plants capture energy from the Sun using a green pigment called chlorophyll.

This energy is used in a process called photosynthesis, which at a basic level of description is:

carbon dioxide + water + light energy > carbohydrate + oxygen

The snow alga does not use chlorophyll in photosynthesis, instead uses a red pigment called carotenoid, as at high latitudes chlorophyll can be damaged by intense sunlight. As they absorb the sunlight, the snow around them melts producing “sun cups”. In winter, they release spores, and in spring use flagellums to propel themselves to the surface where they take part in reproduction.

Respiration is practically the opposite of photosynthesis. This process is:

carbohydrates + oxygen > energy + carbon dioxide + water

There are three convection cells in each hemisphere. The cells sit astride the Inter-Tropical Convergence Zone (ITCZ) along the Equator, and from here warm air rises and moves poleward. As it does so, the air cools and becomes denser and then sinks back towards the surface. This movement of air generates the winds. The Coriolis effect is the result of the Earth’s rotation – prevailing winds in the Northern Hemisphere are deflected to the right, and in the Southern Hemisphere to the left.

As the winds travel over the oceans, some of their energy is transferred to the oceans and currents are formed which move at around 3% of the speed of the winds. The winds and ocean currents are closely correlated.

Currents that are important include the Gulf Stream and the North Atlantic Drift. These currents bring warmth to the northeastern Atlantic, where it is warmer than equivalent latitudes in the northwestern Atlantic. Around Antarctica is the Antarctic Circumpolar Current (ACC) and historically this has been known as the roaring forties and the furious fifties, named after the latitude they were found. This current moves around Antarctica and has isolated the continent from the warmer north.

Formation of ice

Snow crystals are formed by nucleation – this requires the presence of a dust particle or other object around which the crystal forms.

Sea ice forms through the following steps:

• frazil ice – this forms like an oil-slick on the surface
• pancake ice – these can grow to 3m in diameter
• pack ice – often topped with snow, these can grow to more than 2m in thickness

Water is unusual because when it freezes, it becomes less dense than when it is liquid – this is why ice floats on water.

Because sea ice is formed from the sea water, when it melts it does not affect sea level. However, icebergs are formed from falling snow and transported to the oceans by glaciers. When icebergs melt they add new water to the oceans.

Antarctica

In summer the sea ice extends for about 3 million km², but grows to around 16 million km² in winter – this effectively doubles the size of Antarctica. There is an asymmetric growth and decay of sea ice, with the formation of ice taking longer – from February to September – than its eventual decline between October and January.

The ice around Antarctica melts right around the coast in summer, although it is still extensive in the Weddell and Ross Seas throughout the year.

When the ice grows, salt is rejected from the ice, and this causes the density of the water below to increase. This salt rejection, in combination with colder temperatures, causes the water to sink towards the bottom of the ocean to form the Antarctic Bottom Water (AABW). This very dense water flows at great depth towards the Equator.

Another current is formed at mid-latitudes in the Southern Hemisphere, and this is less saline and warmer than the AABW, so is found only to around 1000m depth, and extends towards the Equator.

The Arctic also generates a cold salty current – this is called the North Atlantic Deep Water (NADW). It is less dense than the AABW, so as it flows south, it rises above the AABW, but it is denser than the other Southern Hemisphere current, so sits underneath this.

These currents form a chain right around the world called thermohaline circulation, and so the polar regions are directly influencing the climate right around the world.

Antarctica shows a great range of temperatures. At the coast, average summer temperatures are around -2°C – 0°C, whereas the interior of the continent it is around -20°C to -30°C. In winter the coastal temperatures are around -10°C to -15°C, but the interior can dip to below -70°C. The temperature in the interior falls rapidly and stays fairly constant throughout winter, and this is called the coreless winter.

This means that Antarctica is made up of two climatic zones, and this is compared with the Arctic in the table below:

The Arctic

The Arctic shows a more symmetrical period of ice growth and decline, compared with the Antarctic, with more gradual changes in seasons.

The Arctic shows much more variability in climate than that in Antarctica, with four climatic zones that are summarised in the table above.

This chapter was a general exploration of polar expeditions past and present, and a brief summary of the geopolitics affecting the people of the polar regions.

The polar regions have vastly different environments, and this has had an effect on how long they have been populated. The Arctic, being much closer to most seats of civilisation in Europe, Asia and North America, has been populated since at least the Last Glacial Maximum around 20,000 years ago. The native peoples of the north can collectively be called the Inuit, and they currently number around 200,000 people, scattered right around the Arctic. They did not recognise national sovereignty the way other nations did when they first started exploring these regions.

The Antarctic, being cut-off from the rest of the world by the cold, inhospitable southern ocean, has never been permanently populated, although it now has a fairly large population of scientists year round.

Historical exploration

Commerce and national sovereignty provided the spur for most exploration in the past, particularly with the search for routes to the Far East through the fabled North-West Passage. The expeditions covered briefly in this chapter included:

• the Ancient Greeks including Pytheas who visited the polar region when travelling north from the British Isles
• Viking expeditions to Greenland around the year 980
• Martin Frobisher and Willem Barents search for the NW and NE Passages respectively in the 16th century
• James Cook’s visit to South Georgia in January 1775
• James Clark Ross’ 1839-43 expedition to the Antarctic on board HMS Erebus and HMS Terror – the two volcanic peaks on Ross Island which he discovered are named after the ships
• John Franklin’s ill-fated search for the NW Passage in 1845. He used the same two ships as James Clark Ross’ successful expedition to the southern seas, but Franklin’s expedition led to the death of all the crew and officers. The Scottish explorer John Rae discovered their fate and had reported that there was some evidence of cannibalism.  Unfortunately his letter was published in a newspaper and he was vilified.  He was later vindicated by archaeological research which showed he was correct. Rae also discovered a route through the passage.
• Roald Amundsen sailed the full passage in 1906 – Amundsen of course was later to be the first to the South Pole, in 1911, about four weeks earlier than Scott’s expedition.

The early expeditions definitely had commerce and conquest at their heart, and a very lucrative whaling industry came out of this. I wrote about Philip Hoare’s talk on his book Leviathian or, The Whale in 2010 – Hoare’s book is an excellent look at the impact whaling had.

Exploring for science

Since the very earliest exploration, science has played a big role. For example, Ross’s expedition to the Antarctic discovered a cod icefish, but this wasn’t positively identified until 1904 by Adrien de Gerlache. It has few red blood cells and its blood plasma contains antifreeze proteins which allow it to thrive in the cold polar seas.

Fridtjof Nansen proved that sea ice drifted during an expedition to the north in 1893-1896.

Captain Robert Falcon Scott and Edward Wilson on an expedition to the Antarctic in 1901 discovered that Emperor penguins laid their eggs in winter, and that the birds incubated them upon their feet. In 1911, on Scott’s fateful expedition to the South Pole, Wilson, along with Apsley Cherry-Garrard and Henry “Birdie” Bowers, made a trip to retrieve penguin eggs to try and provide proof for the hypothesis that their embryos would contain evidence of a link between reptiles and birds. This is known as The Winter Journey, and they experienced extreme temperatures and terrible bad luck. But somehow they survived, and Cherry-Garrard told the riveting tale in his stupendous book The Worst Journey in the World.

Scott’s expedition included many scientists, including Frank Debenham who became a leading geologist at Cambridge, George Simpson, who became the head of the London Meteorolical Office, and Edward Nelson who was a senior naturalist at Plymouth Marine Laboratory. Scott’s polar party even carried 17 kg of rocks back with them from the Trans-Antarctic Mountains.  The weight of these rocks may have contributed to their death.

The so called Heroic Age of exploration ended with Shackleton’s death on South Georgia in 1922.

Modern polar science

Exploration has not stopped however.  There has been a continual endeavour to increase knowledge, past highlights include:

• Gino Watkins’ 1930-31 British Arctic Air Route Expedition
• John Rymill’s 1934-37 British Graham Land Expedition

These days, there is an ever changing population of scientists working and living in each polar region. The Amundsen-Scott station at the South Pole has a population of 250 people summer, with 75 there in winter.  It is serviced by the McMurdo Station on the coast which in summer can have a population of 1000 people.

Most science is conducted by national government research organisations, including the British Antarctic Survey, Alfred Wegener Institute for Polar and Marine Research and the Australian Antarctic Division. It’s also not necessary to have people doing the research on location, satellites like CryoSat can provide a continuous stream of data about ice thickness, and other satellites can provide large scale views of continent-sized activities like the break-up of ice shelves.

This chapter covered the geological record of glacial change as well as the factors influencing the climate.

Geological record of change

Fossils found in the Antarctic indicate that it was once much warmer there than today.  Shackleton’s expedition in 1908 found coal, and this indicates that once there would have been trees and other plants growing on Antarctica.

Alfred Wegener once proposed that the continents moved – he called this continental drift, and he thought that the similarity of the shapes of the continents meant that they were once joined together.  Since then, plate tectonics has explained the mechanism by which the continents move.

Continents sit on plates which move; new crust is formed at sea-floor spreading zones, and crust is destroyed at subduction zones.

Wegener wasn’t taken seriously when he proposed his idea, but with plate tectonics and the discovery of fossils like the fern Glossopteris in South America, Africa, India and Antarctica, he has long since been vindicated.

Continents where Glossopteris has been found

The current polar regions were once much closer to the Equator than they are today, and this, along with the fact that the continents were once joined into one enormous continent called Pangaea provides an explanation for the plants, as well as land animal fossils, that have been found in the polar regions.

Proxies

The chapter discussed the use of proxies to explain temperature millions of years ago.  One is the ration of the isotopes of oxygen-18 to oxygen-16.  This is known as delta-O-18 or δ¹⁸O. A proportion is correlated with temperature, and bubbles within ice cores preserve a record of the temperature at the point at which the snow originally fell. The proportion of CO₂ is another proxy.

Milanković cycle

Milutin Milanković built on the work of James Croll to describe the components of the orbital cycle, another important factor in explaining climate. These components combine to describe insolation, or amount of solar energy reaching the Earth’s surface.  The components are:

• the inclination of the Earth’s N-S axis
• the eccentricity of the Earth’s orbit around the Sun
• the precession of the axis – the axis, as seen above the north pole, appears to trace out a circle over 23,000 years

Each of these factors plays a role in determining the Earth’s climate.

Snowball Earth

The Earth has experienced many ice ages, or glacial periods.  We are currently living in an inter-glacial period, which is a slightly warmer period of a glacial period. Towards the end of the Proterozoic there was a long spell known as the Cryogenian (or more popularly as Snowball Earth) during which the Earth was almost completely covered in ice.  One hypothesis for why this occurred was volcanic dust in the atmosphere reducing the amount of solar energy received on the surface.  As the ice increased, so the albedo effect increased, leading to even more ice, this led to a runaway feedback loop.  Further volcanic activity and weathering of rocks releasing CO₂ into the atmosphere are one explanation for how the Earth managed to pull itself out of the freezer.

Formation of current polar regions

By the start of the Cenozoic, 65 Ma, Antarctica was over the south pole. The Antarctic Circumpolar Current (ACC) formed around 35 Ma, and this led to the formation of the East Antarctic Ice Sheet (EAIS).  20 million years later saw the formation of the West Antarctic Ice Sheet (WAIS). This wasn’t a permanent feature at this point, but waxed and waned.  At 8 Ma, the ice sheets in the Northern Hemisphere started to form, including the Greenland Ice Sheet (GIS), the largest extent of ice in the north. By 3 Ma, both the northern ice and the WAIS had become permanent features.

Glaciers

How do glaciers form and move? As snow falls, it slowly accumulates and turns to ice.  This ice gets compacted as more and more snow is added.  Heat from underneath the ice melts the lower parts of the glacier and the pull of gravity pulls the glacier downhill. Cracks and crevasses are formed in two ways: by pools of water that appear on the surface and bore their way into the glacier; and by ripples on underside of the glacier as it moves downhill.

The glacier scrapes off the bedrock as it moves and carries this as moraine.  This is what the brown stripes are in glaciers.

There is a balance determining growth and shrinkage of the glacier.  This is determined by the amount of snow falling (accumulation) and the temperature – the latter affects the rate of melting (ablation).

The formula for this is:

• mass balance of glacier = accumulation – ablation

Surface features showing the effect of glaciers include:

• scrapes along the bedrock, these show the direction in which the glacier flowed
• U-shaped valleys
• glacial erratics – these are rocks that have been carried by the glacier and then dropped as the glacier then retreated

Dust and pebbles from the moraine also falls to the seabed when icebergs melt – these build up Heinrich Layers and are important in determining the rate at which ice sheets melted.

Holocene

We are currently living in a relatively stable period known as the Holocene.  This is characterised by stable temperatures from about 8000 years ago, and this coincides pretty much with the development of agriculture.  The Last Glacial Maximum (LGM) appeared about 20,000 years ago when the temperature was about 9°C colder than today, and the sea-levels were about 120 m lower.

There was a colder period around 12,900-11,600 years which is known as the Younger Dryas. This was a global event and is named after the white dryas flower Dryas octopetela, which is found mainly in mountains and higher latitudes. During this cold spell, this flower’s range expanded.

First of all, samples of the course can be tried, and poster can be downloaded as a PDF or ordered through the OpenLearn website.

I’ve now worked through chapter 1, which outlines a definition of the Antarctic and the Arctic, and gives a broad overview of why the polar regions have the climate that they have. I’ve come across many of the concepts before but will provide an outline of the chapter below.

Both polar regions are named after Ancient Greek words: Arktos which means “to the north”, and Ant Arktos which means “to the south”.

What affects the climate in both polar regions?

The Earth’s axis is inclined at 23.4° to the plane of the orbit around the Sun, this causes the Earth’s seasons as the planet orbits the Sun.  It is summer in the Northern Hemisphere when that side of the Earth is tilted towards the Sun, and winter in the Southern Hemisphere. However, due to this tilt, and the curvature of the Earth, solar energy must pass through more of the atmosphere, and it falls on a wider area, so it is less able to heat the polar regions.

There are four dates that define the seasons:

• 21 March: this is the northern spring equinox when the Sun is directly over the Equator
• 21 June: this is the northern summer solstice when the Sun is directly over the Tropic of Cancer (23.4° N) and the Northern Hemisphere has its longest day of the year
• 21 September: this is the northern autumn equinox when the Sun is directly over the Equator
• 21 December: this is the northern winter solstice when the Sun is directly over the Tropic of Capricorn (23.4° S) and the Southern Hemisphere has its shortest day of the year

Each polar region experiences a polar day, or “midnight Sun” throughout the summer when the Sun does not set, and a polar night during the winter when the Sun does not rise.  The lowest latitudes in which this can be seen are 66.6° N and 66.6° S.  These are the Arctic and Antarctic Circles respectively.

Other factors that affect local climate include albedo which is a measure of the amount of reflectivity of a particular surface. The ocean has an albedo of 3% which means that 97% of energy from the Sun is absorbed by the ocean, a conifer forest in summer has an albedo of 9%, and fresh snow 80-90%.

Different materials also have specific heat capacities, this describes how much energy it takes to increase 1 kg of that object by 1 °C – a metal doesn’t take a lot of energy to heat up, unlike water.

What is energy? Energy (in this example this refers to kinetic energy) describes the speed of movement of atoms or molecules in a substance.  An increase in energy in an object corresponds to increased temperature.

The temperature range over a year in each polar region is approximately 30 °C. The Arctic shows a smooth progression from cold to warmer and back to cold as the year passes, whereas the Antarctic shows sustained periods of constant temperature, with a sharp change before summer and winter.

How is the Arctic and Antarctic defined?

The Arctic is defined using two factors:

• the treeline – the treeline gives way to the tundra in the north
• 10 °C July isotherm – this is a measure of where the mean surface temperature is 10 °C in July

The Antarctic is defined by the Antarctic Circumpolar Current – this current flows clockwise around the Antarctic and separates warmer water in the north from colder water in the south.  This current also forms a Polar Front, south of this is the Antarctic.

The cryosphere

The cryosphere includes all the physical components of the polar environment, and these comprise of seven main parts: icebergs, ice shelves, glaciers, sea ice, permafrost, ice sheets and snow.

The cryosphere is not limited to the polar regions, for example, snow falls in northern Europe and North America, and permafrost is found in parts of the US.

“One of the enriching things about human life is that you relate to other natural things. One loves them, if we don’t love nature, and the Earth, we’re lost.  This is our home, planet Earth.”

This sums Manning up perfectly, his complete and utter awe at the majesty of nature and his feeling of sharing the planet with them, it’s a view of nature that I completely agree with.

His talk was a very quick run through of Scotland’s geology, touching on some of the topics covered in the Men of Rock series from important rock formations that helped provide evidence for the age of the Earth and how the Earth works to the men behind their discoveries, and he also gave some insight into the process of making a TV series.

Scotland has played a big role in the development of geology as a science.  It has some of the most important landforms that have helped explain how the Earth has formed, including Siccar Point, the famous location that made James Hutton realise the world was much older than was believed at the time.  Siccar Point contains a structure now known as Hutton’s Unconformity.  Normally rock is built up over time so that as you move up a section of rock, it gets younger as you move from bottom to top.  This is the case with sedimentary rocks – under the sea sediments washed in from rivers, or the remains of marine life fall to the bottom of the sea, and there they slowly accumulate over time, gradually becoming well known rocks like sandstones and limestones.  Then over time, this rock gets uplifted above the sea to form many of our landscapes today.  Hutton’s Unconformity provides evidence of this uplift, but it also shows another intruguing feature – there is one type of rock, red sandstone, lying almost horizontally atop an almost vertical layer of greywacke. What Hutton realised is that an enormous amount of time would have been required for this feature to form.

Firstly, the greywacke will have formed under the sea, this was then deformed and the rock had risen above the sea.  Then there was a long period of erosion by wind, rain and sea, revealing the steep angled greywacke.  This rock formation was then submerged under the sea again, where the layer of sandstone formed atop it.  There was more deformation and uplift above the sea, and then further erosion, revealing the rock as it stands today. When you realise that the greywacke itself is made of sand, which means that other rocks back in deep time had eroded and formed the basis of this greywacke it really makes the mind boggle at the immensity of time involved.  Geologists throw around figures like 1, 2, 3 billion years like it’s nothing, but if you try and think about it, it is truly impressive just how much time there has been.

Hutton summed up this enormity of time with his famous quote: “no vestige of a beginning, no prospect of an end”.

The rocks in the north west of Scotland have been dated to over 3 billion years, and Stewart also spoke about the Highlands Controversy, the dispute between the geologists Roderick Imprey Murchison, who believed the Silurian period went straight from the Cambrian period to the Devonian, and James Nicol who believed there was a fault between the Moine rocks (that Murchison considered to be wholly Silurian in age) and the underlying Cambrian rocks, and that the Moine rocks were indeed Precambrian rocks, and were part of the rocks underlying the Cambrian rocks, but had somehow been thrust above the Cambrian rocks.  Nicol retreated from public life, and Murchison and his ally Archibald Geikie’s views that the Moine rocks were of Silurian age held sway.

After Murchison’s death, the work of Charles Lapworth and Charles Callaway showed that Nicol was on the right path after all. Geikie felt that his and Murchison’s ideas about these rock formations was under threat and sent two surveyors, Ben Peach and John Horne to the north-west to map the area and confirm finally that the rocks were Silurian, but in the end they showed that Lapworth and Callaway were correct.

Stewart also mentioned other important people in the history of geology, including Arthur Holmes.  He did a quick run-through of where Scotland has been on its journey around the planet, from the deep south near Antarctica, to time spent in the tropics and around the equator, to its current position in the temperate zone right in the middle of a continental plate.

He also spoke about how his TV programmes are very much entertainment, and that they are not designed to educate.  He said he would rather have people in his university classes than learning from TV programmes. He also made the interesting point about how school pupils are introduced to geology-related topics like glaciation and other surface processes within geography at school, and how often these pupils do not go on to study geology as a subject in it’s own right.

His next TV series will be about plants – I’m very much looking forward to that.  As someone with an interest in the boundaries between the biological and physical world, it’ll be fun to watch some programmes that explore the effect plants have on the planet.

HMS Beagle off Fort Macquarie, Sydney Harbour

A recent article in Scientific American: “A Shifting Band of Rain” about the Intertropical Convergence Zone (ITCZ), a band of heavy rain that encircles the globe around the tropics, got me thinking about a short reference they made to the Galápagos Islands. This zone changes latitude depending on atmospheric temperature. As the temperature increases, so the band moves north, and when the temperature cools, the band moves south.

The band currently extends from 3°N and 10°N, with a mid zone averaging 7°N, and it brings rain to the regions beneath it, enabling crop growth like bananas and providing fertile land for people and animals to live on. However, through analysis of sediment cores extracted from islands across the Pacific that range from latitudes just above and below the current ITCZ, Sachs and Myhrvold have been able to build a model of how the ITCZ has changed over the past 1200 years, and the evidence suggests that the ITCZ has moved around from its current position over the past 1200 years. During the Little Ice Age (1400-1850), the mid point of the zone remained south of 5°N. The comment that caught my attention in the article was:

Conversely, the highlands of San Cristóbal Island at 1°S in the desertlike Galápagos archipelago were substantially wetter during the Little Ice Age.” Sachs and Myhrvold (2011, p.57)

What caught my eye was that if the island was wetter than it is today, and it is currently described as being like a desert, does this mean that vegetation and possibly animal life was different at the time Darwin visited the islands in 1835, from what it is like now? After all, 1835 was right at the end of the Little Ice Age, so it may still have been subject to higher rainfall than it gets now.

To help answer my question, I bought and read a book called “The Voyage of the Beagle” by James Taylor, but the book’s focus is elsewhere – it describes the Beagle, which was the third Royal Navy ship of that name – the RN did not allow for currently serving ships to have the same name – it also made me think, as a humorous aside, was the Beagle 2 Mars lander correctly named? Were there other Beagles after FitzRoy’s ship, or should the lander have been called Beagle 2.0 to bring it into line with current nomenclature e.g. Web 2.0?  The ship was converted from a 2-mast brig to a 3-mast barque before it’s first survey.

The book goes on to talk about FitzRoy, who was the Captain of the ship and who selected Darwin as ship’s naturalist and gentleman companion; who had many improvements made to the ship to make it more seaworthy. The book talks about the relationships between the ship’s officers and crew, the artists on board and gives a summary of the types of surveys it was undertaking. The descriptions of the survey is that of a group of people who were very hardworking and who got on very well together. The book is a fascinating account of one the most important episodes in scientific history, but unfortunately, it does not provide answers to my question, so I will read Darwin’s own account of his visit to the islands, as well as FitzRoy’s Narratives which comprise the first two volumes of the joint account of the voyage of the Beagle. I also plan to visit the islands at some point in the future to see the islands for myself.

The image above of the Beagle was painted by Captain Owen Stanley, commander of one of Beagle’s sister ships while the Beagle was in Sydney during it’s third survey (Darwin was on its second survey) and clearly shows it was 3-masted and sits low in water.

References:

Sachs, J. P., Myhrvold, C. L., 2011, A Shifting Band of Rain, Scientific American, 304(3), pp. 52-57

Taylor, J., 2008, The Voyage of the Beagle, London: Conway

Wearing masks, they trapped a crow, in full view of other members of its flock, under a net.  They then, still in view of the other crows, put a sock over its head to keep it calm before fitting it with a leg band.  They then released the bird unharmed.

For the following three years, the researchers observed the behaviour of the birds – over this period, the birds mobbed and scolded people wearing the masks, even if they were within a crowd of other people.  It did not matter if the people wore different clothes, it was the consistency of wearing the masks that the birds identified with.

I found this to be fascinating, I’ve observed Carrion crows Corvus corone standing watching people pass by, it’s possible that they are sizing up people too, determining whether they are a threat or not. It’s amazing to think that a bird is afraid or unafraid of you because of who you are as an individual, and not just as a random human being.

This study is yet more evidence for the intelligence displayed by the Corvids.  I wrote about the antics of the New Caledonian Crow back in 2007.

Reference:

Marzluff, J. et al (2010), ‘Lasting recognition of threatening people by wild American crows’, Animal Behaviour, vol 79, pp. 699-707