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In the last few days you may have been lucky enough to see a shooting star as one of the year's biggest meteor showers was displayed in the skies over Britain. But does a meteor ever become a meteorite? And how do you know if you have found one? Well in this blog I will tell you a little more about meteors and meteorites,  what to do if you think you have found one, and how to find out more at Meteorites Day 2012, a special event at the Museum on 2 September.

 

Over the weekend from the 11 to 15 August the UK was treated to the height of a meteor shower recognised as one of the best and most reliable meteor showers in the northern hemisphere. The Perseid meteor shower happens every year between late July and mid August and at its peak can produce tens of meteors an hour.

 

Originating from the debris stream left by the comet Swift-Tuttle as it orbits the sun, the Perseids are so called because they often appear to come from the constellation Perseus - but as the number of meteors increases they can be seen all across the night sky.

 

You may think that this event would lead to an increase in meteorite discoveries that are reported to the Identification Service here at the Museum, but meteors are formed from very small particles of matter ejected from the comet, that burn up completely in the atmosphere. This means that if you see a meteor you are unlikely to find a resultant meteorite.

 

2012-0402 Iron Meteorite Tanzania (UNK)1.jpgA meteorite discovery from Tanzania

 

But what if you do think you have found a meteorite - what can you do about it? Well before you jump to conclusions there are a few simple tests you can do on your possible meteorite.

 

STEP ONE: Test to see if your discovery is magnetic

 

All meteorites have some degree of magnetism; even the stony meteorites have flecks of iron and nickel mixture throughout the rock that distinguishes them from terrestrial rocks. You should be able to detect the magnetism with an ordinary fridge magnet, so if your object is not magnetic at all - then it is most likely not a meteorite.

 

P1070568.JPGTest your object with a fridge magnet

 

STEP TWO: Check the density of your discovery

 

Meteorites, especially iron meteorites, tend to be far more dense than some of the more commonly mistaken terrestrial rocks, so if your specimen is light in your hand when you pick it up, then again it is unlikely to be a meteorite.

 

P1070574.JPGYour object should be heavy for it's size

 

STEP THREE: Look at the surface of your discovery

 

Meteorites are characterised by something called a fusion crust - when the meteorite comes through the atmosphere the intense heat of entry causes the surface of the meteorite to melt. So if you can see cracks and bubbles or even other bits of rock or mineral stuck to the outside of your discovery, then once again, it is unlikely to be a meteorite.

 

P1070575.JPGThe surface of your object should be smooth with no bubbles (right)

 

So what do you do if you have done these three tests and all three suggest that you have found a meteorite? Then bring it in to the Museum! On Sunday the 2nd of September the Museum are holding a 'Meteorites Amnesty' with members of our Earth Sciences department on hand and some genuine meteorites you can touch and compare against your own discoveries.

 

There will also be talks and activities throughout the day all about meteorites. However, if you miss this event, don't worry. Just send us a photo at the Identification Service email (ias2@nhm.ac.uk) or bring your specimen in on another day and we will let you know if you have a meteorite or a meteor-wrong!

 

Find out more about the Meteorites Day special event at the Museum

1

You only have to browse through the Fossils and rocks forum to see how many of the suspected fossils put on there turn out to be something completely different! Fossil eggs, bones, turtles, ferns, footprints, you name it, natural rock and mineral processes can mimic it. We call these natural rock and mineral specimens that resemble or are mistaken for fossils "pseudofossils". This post doesn't seek to go through the most common look-a-likes, but if you google "pseudofossil" you will find many excellent guides out there.

 

This post is just some of my personal favourites from the last year. Fun and amazingly co-incidental pseudofossils are one of my favourite parts of my job in Earth Sciences identification.

 

2010-2444 mineral thought to be fossil bird head 003.jpg

"Fossil bird head"

 

It's got everything - neck, beak, even an eye. But this shape is created by the growth of a mineral upon the rock surface.

2011-0695 P1040137.JPG

"Fossil shark"

 

This shark shape, silhouetted in white against the dark background, would have me swimming for my life if I saw the silhouette peaking out of the sea. But it is just a chance area of cleaner white Chalk against a backdrop of Chalk discoloured by dirt and moss.

2010-2360 Fossi fish.jpg

"Fossil fish"

 

I can see what they mean, it looks like a guppy with a long flowing tail and fin. But this is a type of the rock flint known as banded flint. Banded flints form a series of roughly parallel lines such as this, which can create all sorts of misleading shapes. The cause is still not fully understood but the movement of water and silica through the flint is thought to be involved.

 

The rock flint can mimic any kind of fossil you can think of - bones, eggs, whole heads and bodies, you name it. Look out for a blog all about the wonders of flint coming soon!

 

2011-0058 dinosaur head pseudofossil 001.jpg"Fossil dinosaur head"

 

If this were a dinosaur, I can even see what kind it would be - one of the duck-billed hadrosaurs I reckon. Sadly, this is just the shape of the lump of rock, that had probably been exaggerated by weathering.

 

 

While writing this I've realised that these pseudofossils do have something in common after all. They all demonstrates one of the key things to appreciate when looking for fossils: don't look for the overall shape of an animal. This is because the soft parts of animals like muscle and skin only fossilise very rarely and in unusual conditions. You can assume you won't come across soft part preservation without knowing what to look for and where to look. To find fossils, look for the hard parts such as bones and shells, and bear in mind these are most often broken, mixed up and/or isolated.

 

Although we can say what these aren't, the hardest question to answer is, so why did the rock or mineral form or weather into exactly that shape? There are millions of rocks out there and so even if such coincidental resemblences are rare, there will still be plenty of pseudofossils. And of course those are the rocks that are going to catch your eye and get picked up.

 

So what should you look for? This page on our website has some good information and links for fossil hunting advice. And of course we will be happy to see whatever you find, whether rock, mineral or uncannily-vegetable-shaped-rock on the rock and Fossil forum here.

 

Happy fossil - and pseudofossil - hunting!

0

How to identify an elephant tooth


A beginner's guide to how we identify a surprisingly common enquiry: mammoth and elephant teeth.

 

elephant tooth web.jpg

 

Left: This tooth was a family heirloom brought in for ID this week. Many elephant and mammoth teeth that are brought in for ID are heirlooms that have been knocking about the house for a couple of generations. This is an Asian elephant tooth. It is a molar, so it's a grinding tooth.

 

Below: Grinding surface of Asian elephant tooth (left) and African elephant tooth (right) in the NHM Mammal gallery. The African elephant tooth has a more diamond shaped pattern to the grinding surface

100_2597.JPG

 

And the elephants themselves in the Mammal gallery - African (top) and Asian (below). Asian elephants are smaller than African elephants and their teeth are smaller on average too.

100_2595.JPG100_2596.JPG

Below. On the left, a mammoth tooth. On the right, a modern Asian elephant tooth.

100_2598.JPG

fossils 010.jpg

 

Left: Mammoth tooth. This was dredged up by a fisherman from the North sea and brought to us for ID. Mammoth teeth have a similar grinding to the Asian elephant, and look different to the grinding surface of the African elephant. And mammoths are indeed more closely related to Asian elephants than African elephants!

 

 

 

 

 

 

 

 

 

 

Mammoth and elephant teeth can be very fragile and tend to crack downwards as you can see here. This can leave isolated plates instead of the whole tooth.

 

Now you can identify elephant and mammoth teeth!

 

Visit out Twitter page at http://twitter.com/NHM_id to see the finds we get in every day