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Many different species in the history of life on this planet have simply ceased to be. Gone but not forgotten these strange animals leave evidence of their existence entombed in the sedimentary layers of the earth's crust. As fascinating as these fossilized discoveries are, what's even more fascinating is the mystery of what happened to them.

The dinosaur's story is certainly the most compelling of all the extinction records. Giants that reigned over the earth their disappearance is both perplexing and intriguing.

New theories are formulated as new scientific discoveries are made but even the experts in the field cannot agree on the facts behind the end of the dinosaur era.

Buried deep in the past, the only clues remaining, point to a number of different theories.

Asteroids Or Volcanoes?

Approximately 65.5 million years ago an event occurred that caused the mass extinction of about 70% of the earth's animal and plant species in a relatively short geological time period. It is called the Cretaceous-Tertiary extinction event or the K-T extinction event. A thin band, a geological signature called the K-T boundary, identifies this.

Around the world dinosaur remains (of the non-avian variety) have only been discovered below this K-T boundary. This points to the conclusion that dinosaurs became extinct either right before the event or because of it.

Luis and Walter Alvarez, along with scientists from the University of California during the late seventies were studying closely the K-T boundary in Gubbio, Italy when they made an interesting discovery. In a clay layer at the boundary point they found 30 times the normal level of a rare element called Iridium. Such high levels of Iridium, it has been theorized, could have only come from two sources: either asteroids or violent volcanic activity.

The Asteroid

Many in the scientific community have postulated this impact event theory. The theory suggests that a large asteroid fell to earth and created a cloud of dust and other aerosols that blocked the sun's rays for up to a year. This reduction in sunlight radically affected plant and animal life causing a change to the atmosphere. At the time of impact a pulse of intense radiation killed many species and the resulting climate change and global firestorms decimated the rest.Dinosaurs, because of their size, were the first to succumb.

Volcanic Activity

The Deccan Traps, located in western India, formed at the end of the Cretaceous period, the same time the dinosaurs disappeared from earth. The Traps are a bi-product of violent volcanic eruptions. This theory postulates that the volcanic activity at the time would have released massive amounts of sulfuric aerosols and ash into the atmosphere again causing a major shift in the earth's climate. A shift that the dinosaurs were not equipped to survive.

Ice Age

Another theory relies on the idea of a major drop in temperature that caused the dinosaurs to die out while allowing the warm-blooded, more insulated mammals to survive. In this case all the plant, animal and marine life that could not adapt to the plummeting temperatures became extinct. A number of scientists pair this theory with the asteroid theory, claiming it was the asteroid that triggered the deep freeze.

There are many plausible explanations and scientific theories regarding the extinction of the dinosaurs. New scientific evidence is discovered all the time, which supports one hypothesis or another, however, the truth is that we really don't know what ended the reign of these giants of the prehistoric world.

It is a mystery that may remain until the moment of our extinction.

Discovery Channel's Dinosaurs blog is one of the best dinosaurs resource available. Covering a wide range of dinosaur topics as they explore their prehistoric existence all the way up to the time of their extinction.

Life is full of obstacles, so I don't think I'm the only person who is tired of being told there's no such thing as an obstacle, that everything should be considered a challenge. If I hear that one more time myself, I may scream. The truth is: life is indeed full of obstacles.

Just ask a 2-year-old, who can't do what she wants to do because some giants prevent her at every turn. Ask the single mom who can't go to school to learn job skills because there's no transportation or child care available. Ask the young man confined to a wheelchair, who can't negotiate the curbs in the neighborhood because the city never got around to sloping them at intersections. Those are not challenges, my friends; those are obstacles!

Ask the 17-year-old who can't pursue any of her career choices because the so-called guidance counselor at her high school says, "People like you are a burden on society. You'll never qualify for higher education, so forget about such silliness." Ask the wife whose abusive husband tells her she's stupid and is only on earth to serve him and his needs.

After either one of those individuals has broken a woman's spirit, it may be decades before she recovers her nerve to try anyway, and by then, half a lifetime has been wasted. Those few existing fairy godmothers are awfully busy people and just don't get around to everyone, young and old, who so desperately needs them.

On the other hand, anyone or anything can look like a failure in the middle. Life is full of obstacles that defeat us at every turn. We need to find ways around them, under them, over them, or, when all else fails, straight through them. And the bigger the hole we leave in our wake, probably the better. Thats called the constructive "I'll show them!" of final frustration.

It's always better to use love to overcome enemies, but some people only respond to being metaphorically hit in the head with a 2 x 4 (not referring to a modified SUV). Certain people come from backgrounds or cultures that only respect those who shove back. This means, for our own protection and that of our families, we sometimes need to caber toss those people who step in our face at every turn.

I'm not talking about breaking the law, or assaulting someone, the way shortsighted, hate-filled people too often do. However, each one of us must stand up, both for ourselves and our dreams. No one can just lie down in the road and wait to be run over again by the same berserk steamroller, or spiked by the same zealot.

Finally, as I've heard Dr. Bertice Berry say, "use obstacles to change yourself and it will change everyone who comes behind you. Don't get caught in the past! Don't let your abuse abuse other people. Don't keep picking at scabs. Just move forward!"

Move forward with love, with great humor and with determination. Persistence and determination will get you from where you are to where you want to be, or very close to it.

(c) 2002 Shirley Ann Parker Reprinted from The Corner Desk, January 2002.

Shirley Ann Parker is the author of Discoveries: A Journey Through Life, an uplifting collection of engaging short stories about the joys and frustrations of family and friendships. Discoveries is available from http://www.bbotw.com Visit Shirley's website at http://www.shirleyannparker.com, and check out her other creative endeavors at http://www.cafeshops.com/topazcoveplus