Thursday, 31 December 2015

Interesting Scientists - William Smith

The Geological Time Scale outlines the history of the Earth.

William Smith was one of the first to explore geological time in an organised way.

He had always been interested in fossils, but in 1794 he was employed to survey the route of a new canal.

He saw that layers of rock lay at a slight angle on top of each other.

Plate from Strata Identified by Organized Fossils illustrating Clay over the Upper Oolite.

This is an illustration Smith drew of fossils in a layer of clay he investigated near Bath.

Each layer had its own set of fossils, distinct from the layers below and above  - this is now called the Principle of Faunal Succession.

Here's how William Smith described his discovery:

". . . each stratum contained organized fossils peculiar to itself, and might, in cases otherwise doubtful, be recognised and discriminated from others like it, but in a different part of the series, by examination of them."

Here is one diagram he drew of part of southern England. The clay layer is a thin blue line over the yellow band of oolite.



It runs from the West, near the River Severn at Tewkesbury, to near London in the East.

These rocks are mainly Jurassic and Cretaceous strata.

In 1815 William Smith published his first Geological Map of England and Wales.

This area covers a similar part of England as the cross-section above.




Wednesday, 30 December 2015

Climate Change - The Greenhouse Effect

What do scientists mean by the "Greenhouse Effect"?

When the Sun's energy arrives at the Earth, it travels through the air.

Some is reflected back to space, but some hits the Earth and warms it.

The warm Earth gives off infrared radiation with various wavelengths.  


Some of those waves can pass back out of the air to space, but some are absorbed by certain gases in the air.


If there are more of those gases, less heat escapes into space.



Concentrated 'greenhouse gases' on Venus have caused the surface temperature to rise to 735 Kelvin (462 degrees C; around 900 degrees F)



Carbon dioxide levels in the atmosphere have risen quickly since people began burning large quantities of fossil fuels.

There was carbon dioxide in the air before that, at around 270 parts per million.

Without any carbon dioxide, the Earth would be very cold.

The temperature would be around -18 degrees C.

There have been times when most of the carbon dioxide was trapped in rocks.

The Earth cooled into a state called 'Snowball Earth'



Tuesday, 29 December 2015

Fossil footprints

Footprints of many kinds of creatures have survived as fossils in rocks.

This can be because they were quickly covered by volcanic ash, or layers of fine clay, preserving the details.

These footprints were most likely made by Australopithecus afarensis, an early human whose fossils were found in the same sediment layer.


They were found at Laetoli in Tanzania.


Looking at much older rocks, footprints of dinosaurs can be used to find out all sorts of things about their lives.


Monday, 28 December 2015

Did Columbus prove the world was round? No, it's an Urban Myth

The idea that Columbus proved the roundness of the Earth still appears from time to time.

It's a myth.

The Round Earth concept dates back thousands of years ... it was known in the time of the Ancient Greeks.

The first person to measure the size of the Earth was Eratosthenes.

He lived from around 276 BC to around 195/194 BC.

So .... Columbus?

He believed in a faulty size of the Earth, smaller than Eratosthenes had found.

He thought it was not very far to India, Japan and China if he sailed across the Atlantic.

This map gives an idea of how Columbus saw the situation.



'Cippangu' is Japan.

If the 'New World' had not been there, his sailors would have starved.  

When did the 'round earth' concept start?

The Greek historian Herodotus wrote about an Egyptian sea voyage, which happened around 600 BC..... around 150 years before his own time.

The fleet sailed South, down the Red Sea, and followed the coast of Africa - all the way to the southern tip (The Cape of Good Hope)

Then West and North, until they turned East, to re-enter the Mediterranean at the Straits of Gibraltar.

When they were in the southern part of their journey, the Sun was in the northern part of the sky.

Many people, including Herodotus, did not believe them.

So... at that time the roundness was not understood.

A hundred years later Aristotle was suggesting the roundness of the Earth.

Sunday, 27 December 2015

Climate Change - The Carbon Cycle

Carbon dioxide is always in the atmosphere as part of the Earth's carbon cycle.

The global carbon cycle transfers carbon through the Earth’s different parts - the atmosphere, oceans, soil, plants, and animals. 

So carbon moves around — it flows — from place to place.



Carbon dioxide (CO2) is the main greenhouse gas emitted through human activities. 

Human activities change the carbon cycle.

First, by adding more CO2 to the atmosphere, mainly by burning fossil fuels.

Also by changing the ability of natural sinks, like forests, to remove CO2 from the atmosphere. 

Human-related emissions are responsible for the increase that has occurred in the atmosphere since the industrial revolution. 




The carbon sinks, on land and in the oceans, have responded by increasing the amount of carbon they absorb each year.

Carbon sinks cope with about half of human greenhouse gas emissions. 

The other half has accumulated in the atmosphere.

Saturday, 26 December 2015

The Pole Star and the Two Bears

In the Northern Hemisphere some of the stars of Ursa Major are easy to see on clear nights.

They make a pattern sometimes called the Big Dipper or the Plough.

Ursa Major and Ursa Minor are the 'Great Bear' and the 'Little Bear'.



The two brightest stars of Ursa Major are known as the Pointers, because they point at the brightest star of Ursa Minor, Polaris, the Pole Star.

The Pole Star, or North Star, has always been used for navigation.



Photographs show that as the Earth turns, Polaris is almost fixed in the centre of the turning star pattern.



Like many stars, the stars of the Plough have Arabic names.

One star, Mizar, is actually a double star.

Alcor probably orbits Mizar, taking around 750,000 years to complete one orbit.

Some people with good eyesight can see Alcor and Mizar as two stars on a clear night.

They can certainly be seen very easily with binoculars.

Friday, 25 December 2015

Orion the Hunter

The constellation of Orion dominates the southern sky during winter in the Northern Hemisphere.



The brightest stars of Orion have wonderful names.

The Red Giant star Betelgeuse marks one shoulder, the other shoulder is marked by Bellatrix.

The three Belt Stars (left to right) are Alnitak, Alnilam and Mintaka.

The knees are marked by Saiph and the very bright Rigel.

Like many star names, they are of Arabic origin.

The stars of Orion act as signposts to other stars seen at the same time of year.




Orion's stars are good examples of some of the wide variety of types of stars.


 

The Sun is really rather small compared to many stars

Thursday, 24 December 2015

Climate Change - The Pliocene Rebooted?

Atmospheric carbon dioxide concentration is now around 400 parts per million (ppm).

It last reached similar levels during the Pliocene, 5.3-2.6 million years ago.


During this period, the area around the North Pole was much warmer and wetter than it is now.

Summer temperatures in the Arctic were around 15 degrees C, which is about 8 degrees C warmer than they are now.

Global average temperatures were 2-3°C warmer than today.

Of course, there were no modern humans at that time.



Hominids of the Pliocene

Nor was there a global system of food supply relying on stable climates for agriculture.

Wednesday, 23 December 2015

Climate Change - Permafrost and greenhouse gases

Arctic permafrost – ground that has been frozen for many thousands of years – is now thawing because of global climate change.


“The release of greenhouse gases resulting from thawing Arctic permafrost could have catastrophic global consequences,” said Dr. Max Holmes, a Senior Scientist at the Woods Hole Research Center (WHRC).


Schematic diagram of greenhouse gases and permafrost.  

Thawing permafrost releases greenhouse gases (carbon dioxide and methane) into the atmosphere, which accelerate climate change, which in turn cause more thawing of the permafrost. 

Tuesday, 22 December 2015

Climate Change - 2015 global temperatures

The US National Oceanic and Atmospheric Administration (NOAA) has released a chart that illustrates how warm 2015 is, compared to the six other warmest years on record. 

2015 is running away with the title of 'warmest year'. 

The reason is a combination of global warming, and a strong El Nino event in the Pacific Ocean.



NOAA also released a comparison to all the years back to 1880, which is when the modern temperature record began.



It's also useful to look at years one by one in another way, colour-coded for El Nino, La Nina and 'neutral' years:




Every La Nina year since 1998 was warmer than every El Nino year before 1995.

Note that 2015 has not yet been added to that chart.

Monday, 21 December 2015

Winter solstice

Summer in the south, winter in the north.

Seasons are caused by the tilt in the Earth's axis.

Winter Solstice is the time of the longest night and shortest day.
























Many ancient monuments are lined up with the solstice, which suggests it was an important moment of the year for many cultures.

One is Maeshowe on Orkney.



Others include Stonehenge and Newgrange.

Winter solstice sunset at Stonehenge in the mid-1980s. Image via Wikimedia Commons.

Sunday, 20 December 2015

Climate Change - Global temperature information for November 2015



The combined average temperature over global land and ocean surfaces for November 2015 was the highest for November in the 136-year period of record, according to the US National Oceanic and Atmospheric Administration.

The temperature was 0.97°C (1.75°F) above the 20th century average of 12.9°C (55.2°F), breaking the previous record of 2013 by 0.15°C (0.27°F). 

This marks the seventh consecutive month that a monthly global temperature record has been broken. 

September, October and November together make up Northern Hemisphere Autumn, and Southern Hemisphere Spring.

The September–November seasonal temperature was 0.96°C (1.73°F) above the 20th century average of 14.0°C (57.1°F). 

This marks the highest departure from average for the season in the 136-year period of record, surpassing the previous record set last year by 0.21°C (0.38°F).

Saturday, 19 December 2015

Climate Change - Oceania


An international team of researchers has produced this graph of ocean levels, for a period of time going back to around 500 BC. 

Oceania is a region made up of thousands of islands throughout the Central and South Pacific Ocean. 

It includes Australia, the smallest continent in terms of total land area.

Many of the nations in Oceania are Small Island Developing States (SIDS).


Many scientists say that Oceania is more vulnerable than most parts of the Earth to climate change, because of its climate and geography. 

The heavily coastal populations of the continent’s small islands are vulnerable to flooding and erosion because of sea level rise. 

Fiji’s shoreline has been receding about 15 centimetres per year over the last 90 years.

Samoa has lost about half a metre per year during that same time span. 

The global sea level graph is from this paper: 


"Temperature-driven global sea-level variability"

Friday, 18 December 2015

Climate Change - Why isn't every year a record year?

Heat can affect things without causing a temperature rise.

Extra heat can be used in ‘changing state’ instead of raising temperature.
A change of state could be … a solid melting to a liquid
Or a liquid evaporating to a gas.

So heat is needed to change ice at zero degrees C to water at zero degrees C.
And to change water into water vapour….. without raising the temperature.
Scientists call the heat used to change state latent heat.
Also, there are natural variations in the global climate, El Nino events being the ones that affect world temperature the most.
The opposite to 'El Nino' is 'La Nina', a cooling effect.
If global temperatures are plotted on a graph in a way that shows these variations, it makes the overall warming trend very obvious.

Bar chart of temperature anomalies 1880-2015 indicating El NiƱe phase
Every La Nina year since 1998 has been warmer than every El Nino year before 1995.

Thursday, 17 December 2015

Climate Change - Deltas at risk

Deltas often form when rivers reach the sea.

The river can carry sand and mud when it is flowing fast.

As the water enters the sea, it slows down, and the sediment drops to make the delta.


Many deltas are at risk from climate change.   This map shows the levels of risk.



An estimated 80 percent of the world's megacities are located in fragile river deltas.   A megacity has a population of over 10 million people.

Over 500 million people live on deltas.

Why are deltas at risk?

One reason is rising sea level, which wears away the delta from the front.

Wednesday, 16 December 2015

The Earth from Space

The Chinese spaceprobe Chang'e 5 took this photograph from space in October 2014.

The spaceprobe was beyond the Moon, looking back at Earth.




This photograph was taken by the Cassini spaceprobe, which is in orbit around Saturn.



The dot marked with an arrow is Earth.

To see the Earth turning in space is amazing - click here for a video.

Finally, an image taken by the NEAR spaceprobe - the Earth and Moon.



Tuesday, 15 December 2015

Climate Change - The Warmest Winter

The northern hemisphere winter , December 2014 to February 2015, was the warmest in the records, according to NASA.
The average temperature, taken for northern land and ocean surfaces, was 
0.79°C above the 20th century average. 

This was the highest for December, January and February in the 1880–2015 record, passing the previous record of 2007 by 0.03°C.


It is interesting to note that there were some 'cold spots'.

Eastern North America was colder than average, and there is an obvious 'blue blob' in the North Atlantic.


In 2015, Boston’s month of snow was a 1-in-26,315 year occurrence.

Monday, 14 December 2015

Climate Change - The 8,200 year event

When the last glacial period ended about 11,500 years ago, the Earth's modern climate began to develop. 

The large continental ice sheets shrank, and sea level rose.


Around 8,200 years ago, however, a major cooling event occurred. 

The 8.2 ka event was first discovered in the Greenland ice core GISP2.

Over two decades temperature cooled about 3.3°C in Greenland.

Temperatures in Europe dropped by around 2°C.

The entire event lasted about 150 years.

Then temperatures warmed, returning to their previous levels. 

So what caused the 8.2 ka event?

As the large ice sheets in Canada were melting, a large meltwater lake formed south of the Hudson Bay. 

Geologists have named this Lake Agassiz, after the 19th century scientist Louis Agassiz.


It was dammed to the north by the Laurentide ice sheet.

Slowly, the ice melted further, and the lake emptied into the sea in a very short period of time.




The cold water flooding into the Atlantic caused cooling, and the rising sea level formed the North Sea and the English Channel, creating the familiar shape of Britain.

This event shows that the climate can react strongly to sudden changes.

Sunday, 13 December 2015

Climate Change - The Atmosphere



Space is not very far away.

Aircraft on long-haul flights travel at a height of about 10 km.

The lowest layer of the atmosphere, the Troposphere, ends at about 15 km.

The air in the layers above the troposphere is very thin indeed.

Think of a place around 15 km (9 miles) from where you are.

That's pretty much how near you are to space.

All the waste gases people dump into the air are trapped in the thin layer of air around the Earth.


Molecules in the air include nitrogen and oxygen as well as water, carbon dioxide, ozone, and many other compounds in trace amounts, some created naturally, others the result of human activity.

In addition to gases, the atmosphere contains extras such as smoke, dust, acid droplets, and pollen.



Atmospheric concentrations of some greenhouse gases over the last 2,000 years. 

Increases since about 1750 are due to human activities in the industrial era. 

Concentration units are parts per million (ppm) or parts per billion (ppb), indicating the number of molecules of the greenhouse gas per million or billion air molecules in an atmospheric sample.