METERORITE TYPES AND CLASSIFICATION

METEORITE TYPES AND CLASSIFICATION

The second in a series of articles by Geoffrey Notkin, Aerolite Meteorites

It is often said that when the average person imagines what a meteorite looks like, they think of an iron. It is easy to see why. Iron meteorites are dense, very heavy, and have often been forged into unusual or even spectacular shapes as they plummet, melting, through our planet's atmosphere. Though irons may be synonymous with most people's perception of a typical space rock's appearance, they are only one of three main meteorite types, and rather uncommon compared to stone meteorites, especially the most abundant stone meteorite group-the ordinary chondrites.

The Three Main Types of Meteorites

What Are Meteorites?

Although there are a large number of sub classes, meteorites are divided into three main groups: irons, stones and stony-irons. Almost all meteorites contain extraterrestrial nickel and iron, and those that contain no iron at all are so rare that when we are asked for help and advice on identifying possible space rocks we usually discount anything that does not contain significant amounts of metal. Much of meteorite classification is based, in fact, on how much iron a specimen does contain.

Iron Meteorites

When I give lectures and slideshows about meteorites to rock and mineral societies, museums, and schools, I always enjoy commencing the presentation by passing around a softball-sized iron meteorite. Most people have never held a space rock in their hands and when someone does pick up an iron meteorite for the first time their faces light up and their reaction is, almost without fail, to exclaim: "Wow, it's so heavy!"

Iron meteorites were once part of the core of a long-vanished planet or large asteroid and are believed to have originated within the Asteroid Belt between Mars and Jupiter. They are among the densest materials on earth and will stick very strongly to a powerful magnet. Iron meteorites are far heavier than most earth rocks-if you've ever lifted up a cannon ball or a slab or iron or steel, you'll get the idea.

In most specimens of this group, the iron content is approximately 90 to 95% with the remainder comprised of nickel and trace elements. Iron meteorites are subdivided into classes both by chemical composition and structure. Structural classes are determined by studying their two component iron-nickel alloys: kamacite and taenite.

These alloys grow into a complex interlocking crystalline pattern known as the Widmanstätten Pattern, after Count Aloys de Widmanstätten who described the phenomenon in the 19th Century. This remarkable lattice-like arrangement can be very beautiful and is normally only visible when iron meteorites are cut into slabs, polished, and then etched with a mild solution of nitric acid. The kamacite crystals revealed by this process are measured and the average bandwidth is used to subdivide iron meteorites into a number of structural classes. An iron with very narrow bands, less than 1mm, would be a "fine octahedrite" and those with wide bands would be called "coarse octahedrites."

Stone Meteorites

The largest group of meteorites is the stones, and they once formed part of the outer crust of a planet or asteroid. Many stone meteorites-particularly those that have been on the surface of our planet for an extended period of time-frequently look much like terrestrial rocks, and it can take a skilled eye to spot them when meteorite hunting in the field. Freshly fallen stones will exhibit a black fusion crust, created as the surface literally burned during flight, and the vast majority of stones contain enough iron for them to easily adhere to a powerful magnet.

Some stone meteorites contain small, colorful, grain-like inclusions known as "chondrules." These tiny grains originated in the solar nebula, and therefore pre-date the formation of our planet and the rest of the solar system, making them the oldest known matter available to us for study. Stone meteorites that contain these chondrules are known as "chondrites."

Space rocks without chondrites are known as "achondrites." These are volcanic rocks from space which formed from igneous activity within their parent bodies where melting and recrystallization eradicated all trace of ancient chondrules. Achondrites contain little or no extraterrestrial iron, making them much more difficult to find than most other meteorites, though specimens often display a remarkable glossy fusion crust which looks almost like enamel paint.

Stone Meteorites from Moon and Mars

Do we really find lunar and martian rocks on the surface of our own planet? The answer is yes, but they are extremely rare. About one hundred different lunar meteorites (lunaites) and approximately thirty Martian meteorites (SNCs) have been discovered on earth, and they all belong to the achondrite group. Impacts on the lunar and Martian surfaces by other meteorites fired fragments into space and some of those fragments eventually fell on earth. In financial terms lunar and Martian specimens are among the most valuable meteorites, often selling on the collectors' market for up to $1,000 per gram, making them worth many times their weight in gold.

Stony-Iron Meteorites

The least abundant of the three main types, the stony-irons, account for less than 2% of all known meteorites. They are comprised of roughly equal amounts of nickel-iron and stone and are divided into two groups: pallasites and mesosiderites. The stony-irons are thought to have formed at the core/mantle boundary of their parent bodies.

Pallasites are perhaps the most alluring of all meteorites, and certainly of great interest to private collectors. Pallasites consist of a nickel-iron matrix packed with olivine crystals. When olivine crystals are of sufficient purity, and display an emerald-green color, they are known as the gemstone peridot. Pallasites take their name from a German zoologist and explorer, Peter Pallas, who described the Russian meteorite Krasnojarsk, found near the Siberian capital of the same name in the 18th Century. When cut and polished into thin slabs, the crystals in pallasites become translucent giving them a remarkable otherworldly beauty.

The mesosiderites are the smaller of the two stony-iron groups. They contain both nickel-iron and silicates and usually show an attractive, high-contrast silver and black matrix when cut and polished-the seemingly random mixture of inclusions leading to some very striking features. The word mesosiderite is derived from the Greek for "half" and "iron," and they are very rare. Of the thousands of officially cataloged meteorites, less than one hundred are mesosiderites.

Classification of Meteorites

The classification of meteorites is a complex and technical subject and the above is intended only as a brief overview of the topic. Classification methodology has changed several times over the years; known meteorites are sometimes reclassified, and occasionally entirely new subclasses are added. For further reading I recommend The Cambridge Encyclopedia of Meteorites by O. Richard Norton and The Handbook of Iron Meteorites by Vagn Buchwald.

About the Author

Photograph by Leigh Anne DelRay

Geoffrey Notkin is a meteorite hunter, science writer, photographer, and musician. He was born in New York City, raised in London, England, and now makes his home in the Sonoran Desert in Arizona. A frequent contributor to science and art magazines, his work has appeared in Reader's Digest, The Village Voice, Wired, Meteorite, Seed, Sky & Telescope, Rock & Gem, Lapidary Journal, Geotimes, New York Press, and numerous other national and international publications. He works regularly in television and has made documentaries for the The Discovery Channel, BBC, PBS, History Channel, National Geographic, A&E, and the Travel Channel. He is currently at work on a book about his adventures as a meteorite hunter, which is expected to be published by Stanegate Press in 2009.
Source: http://www.geology.com

Teaching Plate Tectonics

Teaching Plate Tectonics with
Easy-to-Draw Illustrations

Teaching Plate Tectonics	Teaching Plate Tectonics	Earth's Internal Structure	Divergent Boundary
	Convergent Boundary	Transform Boundary	Tectonic Features Map

The next time you teach plate tectonics, consider a draw-with-me presentation that will engage your students and help them understand the spatial and movement aspects of plate boundary environments.

The process of drawing a picture involves students much more deeply than reading or discussion. This is because drawing gives students an opportunity to visualize sizes, shapes, motions, and spatial relationships. Important facts can be added through annotations and captions. Students remember best when they see and do!

Many students find a draw-with-me presentation an enjoyable experience. Drawing enhances their learning, understanding, and retention processes. And, at the end of the class session, they have a set of illustrations that can be used for study, reference, and communication purposes.

I have used the illustrations on these pages (see menus at page top and bottom), with only minor modifications, to lead students from primary grades through graduate school in lessons about plate tectonics, volcanoes, earthquakes, and the rock cycle. When time allows, I always opt to draw these illustrations step-by-step with my students. It’s fun that way!

When time is short, presenting pre-drawn illustrations on an overhead projector can be a good alternative. With this methods you start with a basic drawing and then annotate it with important features. This works best when your students have photocopies of the illustrations to which they can add important details and annotations.

For your convenience, starting point drawings of all illustrations used in this lesson are included in my Plate Tectonics Guidebook . Please feel free to use these illustrations in any way that will enhance your teaching. And, if you have time, draw them once for me.

Hobart M. King
Publisher, Geology.com

WHAT ARE METEORITES?

WHAT ARE METEORITES?

The first in a series of articles by Geoffrey Notkin,

Aerolite Meteorites

About the Author

Photograph by Leigh Anne DelRay

Geoffrey Notkin is a meteorite hunter, science writer, photographer, and musician. He was born in New York City, raised in London, England, and now makes his home in the Sonoran Desert in Arizona. A frequent contributor to science and art magazines, his work has appeared in Reader's Digest, The Village Voice, Wired, Meteorite, Seed, Sky & Telescope, Rock & Gem, Lapidary Journal, Geotimes, New York Press, and numerous other national and international publications. He works regularly in television and has made documentaries for the BBC, PBS, History Channel, National Geographic, A&E, and the Travel Channel. He is currently at work on a book about his adventures as a meteorite hunter, which is expected to be published by Stanegate Press in 2009.

Welcome!
Welcome to the first edition of Meteorwritings.

I am a science writer, photographer, and professional meteorite hunter. I travel the world looking for actual rocks from outer space, and I write about my adventures for both scientific and popular magazines. I have also made documentaries about meteorite hunting for PBS, National Geographic, The History Channel, and the Travel Channel. I was thrilled by the invitation to contribute to Dr. King's Geology.com and in the months ahead I will discuss the origins of meteorites, what they are made of, why they are valuable to science and collectors, and even how to find and identify them. I hope to share my enthusiasm for these amazing visitors from deep space.

What are Meteors?

Every year hundreds of hopeful people contact me because they believe that an unusual or out-of-place rock they have found is a meteorite. I frequently receive emails which contain an amusing but impossible statement along the lines of: "I think I've found a meteor."
In order to appreciate the humor inherent in this sentence we must first understand the difference between meteors and meteorites. Meteor is the scientific name for a shooting star: the light emitted as fragments—usually rather small—of cosmic material which we sometimes see at night, burning high up in the earth's atmosphere. The bright, and typically very short-lived flame, is caused by atmospheric pressure and friction as pieces of extraterrestrial material become so hot they literally incandesce, as does the air around them. Manned spacecraft such as NASA's space shuttle and the Mercury, Gemini, and Apollo capsules experienced similar heating during re-entry into our atmosphere, which is why they employ heat shields to protect the astronauts and cargoes inside.

Meteor Showers

There are a number of periodic meteor showers visible each year in the night sky: the Perseids in August, and the Leonids in November usually being the most interesting to observe. The annual meteor showers are the result of our planet passing through debris trails left by comets. The meteors we see during those annual displays are typically small pieces of ice which rapidly burn up in the atmosphere and never make it to the surface of our planet.

Sporadic Meteors

An sporadic is a meteor which is not associated with one of the periodic showers and the majority of those meteors also burn up entirely in the atmosphere which acts as a shield, protecting us earthbound humans from falling space debris. Any portion of a meteor which does survive its fiery flight and falls to the surface of the earth is called a meteorite. So, meteorite scientists and hunters understandably chuckle to themselves when a hopeful person claims to have discovered a meteor. The excited people who ask me to help them identify a strange rock should actually be saying: "I think I've found a meteorite."

A polite and charming lady once telephoned the Aerolite Meteorites office and asked if we had, for sale, any meteorites from the constellation of Castor and Pollux. I explained to her that most—or possibly all—meteorites found on earth originate from within the Asteroid Belt between Mars and Jupiter, but there is a chance that some meteorites come to us from farther afield. It has been theorized that rare carbon-bearing meteorites known as a carbonaceous chondrites—such as Murchison which fell in Victoria, Australia in 1969—may be the remnants of a comet nucleus, but that remains conjecture. The stone meteorite Zag, which was seen to fall in the Western Sahara in 1998 and later recovered by nomads, contains water and so a slightly more fanciful but intriguing theory developed which suggests that large meteorites may have carried both water and amino acids (the so-called "building blocks of life") to our planet in the distant past.

What are Meteorites?

Meteorites are rocks, usually containing a great deal of extraterrestrial iron, which were once part of planets or large asteroids. These celestial bodies broke up, or perhaps never fully formed, millions or even billions of years ago. Fragments from these long-dead alien worlds wandered in the coldness of space for great periods of time before crossing paths with our own planet. Their tremendous terminal velocity, which can result in an encounter with our atmosphere at a staggering 17,000 miles per hour, produces a short fiery life as a meteor. Most meteors burn for only a few seconds, and that brief period of heat is part of what makes meteorites so very unique and fascinating. Fierce temperatures cause surfaces to literally melt and flow, creating remarkable features which are entirely unique to meteorites, such as regmaglypts ("thumbprints"), fusion crust, orientation, contraction cracks, and rollover lips. These colorful terms will be discussed and examined in future editions of Meteorwritings.

Meteorites: Very Rare and Very Old

Meteorites are among the rarest materials found on earth and are also the oldest things any human has ever touched. Chondrules—small, colorful, grain-like spheres about the size of a pin head—are found in the most common type of stone meteorite, and give that class its name: the chondrites. Chondrules are believed to have formed in the solar nebula disk, even before the planets which now inhabit our solar system. Our own planet was probably once made up of chondritic material, but geologic processes have obliterated all traces of the ancient chondrules. The only way we can study these 4.6 billion year old mementoes from the early days of the Solar System is by looking at meteorites. And so meteorites become valuable to scientists as they are nothing less than history, chemistry, and geology lessons from space.

Gemstones from Space

Some meteorites even contain gemstones. The beautiful Brenham pallasite, found in Kiowa County, Kansas is packed with sea-green olivine crystals, which is also known as the semi-precious gemstone peridot. Both the Allende meteorite which fell in Chihuahua, Mexico, and the Canyon Diablo iron which formed Arizona's immense and erroneously named Meteor Crater (craters are formed by large meteorites, not meteors) contain micro diamonds.
The rarity of meteorites, along with the fact that they are the only way in which most of us will ever have the chance to touch a piece of an alien world, make them of great interest to an ever-expanding network of private meteorite collectors. Meteorite collecting is an exciting and growing hobby and there are perhaps a thousand active enthusiasts in the world today. The international space rock market is something else we will explore in the months ahead.

Sumber: http://www.geology.com

Memahami teori evolusi dari diri sendiri

Memahami teori evolusi dari diri sendiri

Don't trust evolution, it is just a science, not for believer

Memahami teori evolusi mirip memahami kemunculan kita atau kelahiran diri kita di dunia.

Ketika kita lahir ceprot ! Tak ada yang dapat meyakinkan kita bahwa kita lahir pada jam itu, tanggal itu dan oleh ibu itu dengan sang ayah yang itu. Yang ada hanyalah selembar surat. Dan kesaksian mereka. Kita yakin itu adalah tanggal kelahiran kita tanpa kita mampu membuktikannya atau menolaknya.

Ketika umur sekian bulan ada foto-foto kita. Juga ketika TK, SD. Nah saat itu kita baru punya ingatan. Pertanyaan yang mungkin agak sulit tentang mulainya sejarah diri kita sendiri, “kapan saat terkecil yang anda ingat ?“. Saya yakin ndak ada yg ingat saat dilahirkan. Ndak ada yg ingat wajah doker, atau bidang yg menolongnya.

Skalilagi kita hanya percaya pada selembar surat dan selembar foto, serta pengetahuan dari orang yg tahu tentang masa kecil kita. Jarang diantara kita yang kemudian melakukan checking dan recheck ke Rumah sakit atau bertanya pada bidan yang membantu ibu melahirkan kita. Juga ndak ada yang berniat membuktikan apakah kita keturunan ayah dengan uji DNA. Namun rata-rata hanya percaya saja dengan surat dan cerita dari orang tua yang sudah ada saat kita lahir.

Sumber data dan sumber ilmu

Teori evolusipun berevolusi

Saya ibaratkan surat akta lahir itu sebagai sebuah data sumber ilmu pengetahuan. Orang tua, pakdhe, budhe dan om-tante adalah para alhi. Yang kebetulan dituliskan dalam selembar kertas. Dan ketika saat terkecil munculnya kita adalah saat munculnya kesadaran. Kapan itu ? Saya sendiri hanya ingat masa terkecil saya ketika usia 3 tahun. Itu saat termuda yang mampu saya ingat. Walaupun tetep samar-samar. Tetapi saya ingat lokasi dan dengan digendong almarhum bapak saya. Setelah itu memori saya barulah saya mampu merunut kehidupan saya telah berjalan setapak-setapak hingga kini.

Foto-foto lain serta tulisan serta memori yang ada di otak saya menjelaskan perjalanan hidup saya sejak bayi (yg saya tidak ingat sama sekali) hingga kini ada di Jakarta.

Evolusi mahluk dan perjalanan hidup

Nah bisa kita mengibaratkan foto-foto itu sebagai fosil fosil. Saya bisa percaya fosil itu sisa mahluk hidup masa lampau. Layaknya saya melihat foto masa bayi saya ketika tengkurap. Sayapun hanya percaya itu foto saya karena diberitahu om, pakde serta ortu saya. Demikian juga fosil-fosil itu. Saya lihat foto saya bayi mirip dengan saya. Dan berkembang menjadi saya. Saya juga melihat fosil-fosil itu berkembang berubah seperti layaknya perubahan yg perlahan.

Kalau saya bisa dan mampu mengerti foto-foto itu adalah foto-foto perkembangan saya sejak dahulu, maka secara sederhana saya juga meyakini fosil2 itu sebagai jejak napak tilas perubahan mahluk hidup. Dan dengan begitu saya mudah mengerti bagaimana proses evolusi itu berkembang.

Ita, sejak bayi hingga kini

Disebelah ini foto perkembangan sahabat saya, Ita (Alphita) yang dikumpulkannya sejak kecil. Di atas memeperlihatkan Ita yang masih bayi, tentusaja kalau ditanya dia tidak akan bisa ingat sewaktu bayi. Tapi saya yakin dia percaya saja bahwa itu dirinya. Tentusaja selain dengan dongengan kakek nenek serta ibu-bapaknya, Ita juga melihat perkembangan wajah dirinya. Dan itu yang akan membuatnya percaya bahwa foto bayi dan anak kecil itu adalah dirinya.

Nah kita tahu ada fosil yang terrekam dalam batuan merupakan sisa mahluk hidup masa lalu prosesnya bisa dilihat ditulisan ini Apa itu fosil ?. Tentusaja fosil-fosil ini tidak terrekam lengkap. Mirip seperti rekaman foto kita juga terpencar-pencar. Karena dulu belum ada filem yg merekam perjalanan kita sepanjang masa. Namun dengan fosil inilah para ahli mempelajari proses perubahan mahluk hidup dan melahirkan teori evolusi.

Tentusaja perubahan individu ini akan berbeda dengan perkembangan mahkluk hidup secara kolektif.  Perubahan yang terlihat dalam proses evolusi bukanlah perubahan individu, juga bukan perkembangan satu keluarga saja, tetapi perubahan kolektif spesies selama jutaan tahun. Namun harus dimengerti juga bahwa kita pun memiliki keterbatasan kesadaran dalam memahami sejarah diri sendiri. Demikian juga teori evolusi. Teori ini memiliki titik-titik simpul yang masih lepas tak berhubungan. Mirip seperti sulitnya memahami rekaman sejarah diri kita sewaktu bayi.

Sumber: dongeng geology. https://rovicky.wordpress.com/2011/05/02/memahami-teori-evolusi-dari-diri-sendiri/

Einstein: “Saya Tidak Pintar-pintar Amat”

Einstein: “Saya Tidak Pintar-pintar Amat”

“Yang bener ah?” Serius, dia sendiri koq yang ngaku begitu. “Dia kan termasuk orang paling jenius di dunia?” Memang, tapi kenyataannya dia mengatakan seperti itu. “Mungkin hanya merendah.” Bisa jadi! Tapi, saya yakin ada kebenaran dibalik perkataan yang dia sampaikan. Apa itu?

OK, saya akan tunjukan kalimat lengkapnya:

It’s not that I’m so smart, it’s just that I stay with problems longer.

Saat dia mengatakan, It’s not that I’m so smart, bisa jadi hanya sebuah cara untuk merendah diri. Namun saat dia mengatakan, it’s just that I stay with problems longer, saya yakin ini adalah suatu kebenaran. Dia adalah tipe orang yang berpikir keras. Inilah yang menyebabkan dia jenius.

Dari perkataan itu saya mengambil 2 kesimpulan:

• Dia berpikir keras saat memikirkan suatu masalah atau soal. Dia tidak mudah menyerah untuk mencari jawaban dari permasalahan yang dia hadapi. Memang seperti inilah karakter orang jenius. Mungkin Anda ingat cerita Archimedes dimana dia terus memikirkan masalah bahkan saat dia mandi. Jadi jangan cepat menyerah! Saat ini mungkin tidak bisa, tapi bisa jadi setelah berusaha,  menjadi bisa.
• Saat dia tidak menemukan jawaban dengan suatu tingkat pikiran, dia meningkatkan tingkat pikirannya. Atau menggunakan 6 cara berpikir seperti dijelaskan oleh Edward de Bono. Yang jelas, dia terus meningkatkan cara berpikirnya untuk menemukan suatu jawaban. Di lain kesempatan dia mengatakan,

No problem can be solved from the same level of consciousness that created it.

Apa hikmah untuk kita?

Sebelum membahas hikmahnya, saya akan sedikit menjelaskan kata masalah atau problem bukan berarti kita hanya berpikir saat kita mengalami masalah sesuai pengertian kita sehari-hari. Tetapi termasuk saat kita akan melakukan peningkatan atau perbaikan. Misalnya, masalahnya: “bagaimana cara meningkatkan penjualan?”

1. Jangan cepat menyerah saat Anda sedang berpikir menyelesaikan suatu masalah. Mungkin diperlukan berpikir lebih keras, lebih kreatif, dan menggunakan teknik-teknik berpikir. Mungkin perlu diam sejenak menenangkan pikiran untuk mendatangkan ide intuitif. Mungkin perlu bertanya ke seseorang. Mungkin perlu buka buku.
2. Tingkatkan terus pola pikir Anda. Bisa jadi masalah Anda tidak akan terselesaikan dengan tingkat pikiran Anda saat ini.

Sumber: http://www.motivasi-islami.com/einstein-saya-tidak-pintar-pintar-amat/