The Earth Story

Timelapse of the sky and night over ancient castles of Spain.

The Ancient Amazon was once a thriving metropolis When one thinks of the lush Amazon rainforest, an ancient flourishing metropolis probably isn’t the first thing that comes to mind. The Amazon is the Earth’s largest rainforest, spanning an area of 6.7 million square kilometers across nine countries, and is home to one-tenth of world’s known species. Trying to survive the Amazon, let alone attempting to build a functioning society, is a pretty grim task, and scientists believed that the Amazon had always been an untouched wilderness before the modern era of deforestation. Yet archaeologists have found evidence that complex societies had existed in the Amazon for thousands of years, and that the wilds of the Amazon only reclaimed these settlements in the past few hundred years.

Where in the Earth would you be the heaviest? Standing on the surface of Earth, or in orbit around the Earth, to a first approximation the gravity of the planet is no different whether the planet has a lot of mass right at the center or has mass evenly distributed throughout, or has all its mass right at the surface. However, if you moved down through the planet, the gravity will change. If all Earth’s mass was at the center, you’d find that gravity increased as you approached the center, then dropped right as you reached it. If most of Earth’s mass was near the surface, you’d find gravity gradually decreased as you moved towards the center.

Shaking Shutdown

Much of modern life makes noise that subtly shakes the earth below. Trucks moving along roads, hammers in a building going up, even people walking along the street. To a seismograph, these little vibrations are nothing but “noise” – a constant background shaking that is measured today as little wiggles in the electronic sensors in the device. At the beginning of 2020, something unprecedented happened.

How far to the Horizon: How to work out if you really can see your house from here!

As a child I was told by my dad that when you look out across a flat plain the furthest you can see is 21 miles due to the curvature of the Earth. I only remembered this recently; a friend of mine having a flat overlooking Manchester and the rising hills of the Peaks beyond. We stood on her balcony debating how far we thought the hills were away, and it occurred to me that it depends very much on how far we could see before the Earth curved away from us.

The picture below shows the view of the English coast from France, so how far exactly can you see given a clear day and no obstructions?

As a geologist I generally avoid maths, especially when the maths in question appears to have stolen several members of the English and Greek alphabets. Despite this I have persevered for you lucky readers and below can now reveal how far away the horizon really is.

Firstly my father was both right and wrong. We can only see so far due to the curvature of the Earth, however this distance isn’t a constant number. This is because it is dependent on how high above the Earth’s surface we are observing the horizon from. For example, you can see far more of the surrounding landscape from the top of a mountain than you can lying on the floor.

Now, I could go on to use pythagoras’ theorem and prove to you all how we get to the two constants I’m about to show you. However, I shall refrain from doing so but if you do enjoy your maths and working things out from basic principles check out the links below because some lovely people of the internet have done all the explaining for me. The rest of you will just have to believe me that these equations make sense.

So to work out the distance to the horizon you need to multiply the square root of your eye height in feet (your actually height in feet won’t make too much difference) by 1.23. This will give you the distance to the horizons in miles. If you want those figures in metric you simply multiply the square root of your eye height in metres by 3.57 to give you the distance to the horizon in kilometres.

Simple right? Well technically you should take into account refraction due to the air being denser closer to the Earth’s surface. So now just use the constants 1.32 or 3.86 respectively and you can work out if from the top of a mountain you would be able to yell ‘I can see my house from here!’.

For example, If you lay flat on the floor the horizon would be less than a mile away, however if you were stood at the top of a 1000m (3,280ft) mountain you would be able to see 112.8km (67.7 miles), pretty cool right?

There are a few other variables such as you can see further when the sun is setting than during the day, but as a rough measure of distance to the horizon these equations are fairly accurate. So the next time you’re wondering just how far it is to that mountain/skyscraper/bar on the horizon thank whatever deity it is you believe in for our Earth being round, because had it been flat that bar would be much further away!

Further Reading:

http://bit.ly/1FK7Pjr

http://bit.ly/1FK7P2N

http://bit.ly/1E8QCuH

Image Credit: Rolf Süssbrich

The belt of Venus and our world's shadow Every sunny day around dawn and dusk, the shadow of our planet appears opposite the solar orb, often lined with pink and purple colours. So named because it is the zone where the morning and evenstar appear (since the inner planets are never very far from the sun as seen from earth), it is most clear when the air is dusty and the sky cloud free. The pinks are due to backscattered light off the dust in the atmosphere, at the edge of the world's umbra. In this case, the sun was rising over Lapland, and the ice covered trees formed a beautiful backdrop to a wonderful and common sight, which becomes more awe inspiring when we remind ourselves that we are seeing our planet's shadow extending off towards space. Loz Image credit: Niccolò Bonfadini http://bit.ly/1aWZrAF https://www.yahoo.com/news/photos/arctic-circle-transformed-into-ghostly-world-slideshow/arctic-trees-photo-1343068100.html

Local Sea Level Rise- one of the trickiest predictions, part 2: Glacial rebound

In the first post of this series we mentioned that the melting of the large Greenlandic and Antarctic Ice Sheets could actually result in lower sea levels around those regions. In the first post (http://on.fb.me/1C2B9Lx ) we explained how gravity can influence sea level rise. In this second series post, I will explain the ‘glacial rebound’ occurrence.

Glacial rebound affects areas that currently have, or once had large ice sheets or glaciers covering them. In the last glacial maximum, ice sheets covered much of North America (Laurentide Ice Sheet), Northern Europe (Weichselian Ice Sheet) and South America (The Patagonian Ice Sheet). The only current ice sheets are the Greenland Ice Sheet and Antarctic Ice Sheet. These huge ice sheets are so heavy that they actually sink the earth’s crust beneath them. As they melt and lose mass, the earth begins to rise again, a result of the reduction of downward pressure. Many locations are still experiencing this glacial rebound from the previous ice age, for example parts of Canada and Scandinavia are rising which ‘offsets’ sea level rise in those areas. On the contrary, places such as the south of England and Chesapeake Bay are sinking, as the land was squeezed upwards from the downward pressure of the ice sheets nearby, exacerbating the effects of sea level rise. An extreme example of this has been reported from Finland, where researchers from the Finnish Meteorological Institute predicted a 29cm sea level rise in the Gulf of Finland and a 27cm fall in the Bay of Bothnia by 2100! In the Bay of Bothnia, uplift is estimated to be up to 9.9mm/year.

The image is from Ilulissat Isfjord in Greenland where the Jakobshavn Glacier calves into, producing around 10% of the icebergs from Greenland (and possibly the source of the iceberg that sunk the Titanic).

Image credit: My own.

References/Further reading: IPCC on sea level rise: http://bit.ly/1CrvtOk

Johansson, M. M., Pellikka, H., Kahma, K. K., & Ruosteenoja, K. (2014). Global sea level rise scenarios adapted to the Finnish coast. Journal of Marine Systems, 129, 35-46.[_

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Incredible views of this planet from the Himawari 8 weather satellite. Original caption:

This captivating photo was taken by astronaut Barry Wilmore, commander of Expedition 42 to the International Space Station (ISS). Through a haze of cloud covering parts of Spain and Africa, we can see the lights of civilisation, smouldering, as if on fire. We love photos like this here at The Earth Story, as it puts our planet back into perspective. Earth, for the moment, is truly one of a kind and one thing that all of us have in common, is that we share it; our home. -Jean Image courtesy of Barry Wilmore.

The Earth - not a perfect bar magnet

Do you carry around a smartphone? If you do, you’re carrying a map like this one with you.

Have you ever adjusted a compass for “Declination”? You’ve also dealt with this map.

Smartphones have a compass built into them able to detect Earth’s magnetic field. The magnetic field is generated deep within our planet’s outer core, created by flowing, super-heated, liquid iron that carries electrical currents and charges. The magnetic field of Earth mostly points north south, showing that the Earth’s rotation affects the motion in the core, but it isn’t quite perfect. There are lots of subtle variations in the magnetic field, such that magnets at most spots on the Earth don’t point directly at the North Pole. 

We don’t understand what is happening in the core well enough to predict exactly how the magnetic field is going to change over time, but we can predict that areas that are currently weakening or strengthening will keep doing that. Those predictions usually work for several years but lose accuracy farther out.

This magnetic declination map was released earlier this year - delayed in part by the US Government Shutdown. It shows the separation between the north pole as pointed to by a compass, and true north - the axis the planet rotates around. It combines the fact that the magnetic and true north poles don’t line up with the small-scale features on the Earth’s surface and allows phones and compasses to correct for these variations.

The lines marked in green are the only places on the globe where a compass with no calibration will point directly to the North Pole. Everywhere else on the Earth, compasses and smartphones need corrected to one side or the other.

A map like this for 2019  is now on your smartphone whether you know it or not. Every app that uses the compass to determine direction makes use of it. You’re carrying around the work of the World Magnetic Model in your pocket.

-JBB

Image credit: WMM https://www.ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml

Original caption:

It’s rainin’ rocks

This map should make us all take a moment and go hug the atmosphere. No, you figure out how, it earned it.

When a rock enters earth’s atmosphere, it releases a lot of energy and often explodes, producing shock waves in the atmosphere that have been detected by a U.S. Government monitoring program. These events are called bolides, and this map shows the location of bolides beyond a certain size in Earth’s atmosphere over a 20-year period from 1994-2013.

This map shows a total of 556 events, basically 1 every 2 weeks, on average. The largest explosion in that time was the Chelyabinsk event in 2013, when an asteroid about 20 meters in diameter entered the atmosphere, exploded, and fragmented, damaging cities in Russia near the shock.

The smallest dots on this map are much weaker than Chelyabinsk – objects about a meter in size entering the atmosphere and vaporizing or exploding produce them. Those are pretty harmless most of the time, but they still release the same energy as 5 tons of TNT exploding. The difference between a barely-detectable blast and something that can severely damage a city, therefore, is the difference between a chunk of rock 1 meter wide versus 20 meters wide - the Chelyabinsk explosion is estimated to have released the same energy as a 500 kiloton nuclear bomb.

As Earth orbits around the sun, it is literally in a shooting gallery of debris; rocks left over from the formation of our solar system hit this planet all the time, as this map shows. The locations of these events appear random, indicating that stuff flies in from all sides with no obvious pattern. By having this data over a 20 year period, scientists will be able to use statistics to estimate how often we can expect large explosions, the scale of Chelyabinsk or larger, in the atmosphere, and use that understanding to gauge how much we need to prepare for larger impacts.

If it weren’t for our atmosphere, most of these rocks would be hitting Earth. Instead, the thin layer of air above it does a remarkable job at keeping things off our heads. We owe it some thanks for that favor.

-JBB

Image credit: NASA/JPL http://neo.jpl.nasa.gov/news/news186.html