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Carlo Calanti, age 12, of Toronto, Ontario, Canada, for his question:

What do they mean by a petrified forest?

In everyday language, a petrified person is in a panic and too scared to move a muscle. "Petrified" originally meant turned to stone    and this actually happened to certain ancient forests. A somewhat similar state of frozen immobility overtakes a person said to be petrified by panic.

The famous Petrified Forest of Arizona is a picture book desert, painted with rainbow rocks under the enormous dome of a dazzlins~ blue sky. The scene has been this way for several million years. But to a trained eye, the place is strewn with evidence that the region was very different in the dim, distant past.

You may bash into a bit of this evidence. Suppose you sari what seems to be a branch or a fallen log, lying right there on the ground among the colorful desert stones. If you happened to kick the woody object, you would regret it. When the agony sub¬sided, you mould be ready to learn that the object is a petrified piece of wood made of super hard stone. Simply stated, you innocently used your kicking muscles to bash your toe on one of the hardest chunks of stone in the earth's crust.

The story goes back at least 150 million years, when forests of living trees thrived in this area. Later, a change in climate robbed the region of its moisture and the magnificent forest trees perished from thirst. Their enormous trunks toppled into what had become a desert region of arid sands. Some fell into old riverbeds and forsaken waterways. In time, desert winds piled desert sands above and around the fallen forest giants.

The rocky, bone hard ground was short of oxygen. Decay bacteria need this vital element to live and perform their demolition duties on discarded organic material. The fallen trees neither rotted nor decayed. Meantime through millions of years, scanty desert showers percolated down through the surface and accumulated pockets of lazy ground water. In time, it dissolved loads of assorted silicates from the sandy minerals.

The ground water also percolated through the old fallen trees. Patiently, very patiently their organic chemicals were gently, very gently washed away. The real miracle occurred as the woody substances were replaced by super hard silicate chemicals, left by the lazy mineral rich ground water. Gradually, these mineral deposits replaced the woody tissue, copying the original cells and tree rings, molecule by molecule.

In time, the woody remains of the ancient forest mere turned to stone, which is the original meaning of the word "petrified". The copy was made with age old patience in finest detail. The quality materials used were molecules of semi precious sili¬cates, including rainbow colored quartzes and opals, jaspers and flower tinted agates.

 

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