THIS IS AN OFFICIAL EARTHCACHE

The humber river is home to many plants, animals, wildlife and a thing many don't know about : Fossils.  You may be wondering how fossils are formed, here's how.

How do fossils form?

Not many plants and animals are lucky enough be turned into fossils.

When an animal or plant dies its remains usually rot away to nothing. Sometimes though, when the conditions are just right and its remains can be buried quickly, it may be fossilised. There are several different ways fossils are formed. Here we go through the five steps of fossilisation to make a typical 'mould and cast' fossil.

An animal dies, its skeleton settles on the sea floor and is buried by sediment.

An animal dies and its body sinks to the sea floor. The soft parts of the animal rot away, leaving only its skeleton. The skeleton is buried by sediment (like mud or sand) falling from the ocean above. The sea floor is an ideal place for fossilisation, which explains why many fossils are marine (from animals that lived in the sea). Land animals may die and be swept out to sea to be buried in the same way.

The sediment surrounding the skeleton thickens and begins to turn to stone.

The skeleton continues to be buried as sediment is added to the surface of the sea floor. As the sea floor sinks, pressure increases in the lower layers of sediment and it turns it into hard rock.

The skeleton dissolves and a mould is formed.

Now buried at depth and surrounded by stone, the skeleton is dissolved by ground water. This leaves a cavity (or hole) preserving the shape of the original skeleton. This cavity is known as a natural mould.

Minerals crystallise inside the mould and a cast is formed.

Water rich in minerals enters the mould, and fills the cavity. The minerals deposited in the mould form a cast of the mould. This cast has the same shape as the original skeleton, but none of its internal features.

The fossil is exposed on the Earth's surface.

Millions of years later, the rock surrounding the skeleton rises to the Earth's surface (this happens during mountain building, earthquakes and other earth processes). The rock is worn away by wind and rain, and the fossil is now exposed, waiting to be found!

A creature makes its way doggedly along the sloping floor of a shallow, subtropical, Paleozoic sea. Its body is low, flat, and roughly the size of a phone book. The eight segments of its thorax separate a triangular tail from a nearly-identical triangular head. From the latter protrude two bulging, calcified compound eyes. The top of its body is protected by a hard, mineralized exoskeleton. Underneath, it collects oxygen from the water through gill filaments attached to its tiny articulated legs. Two long spines extend backward from the corners of its head. It is a trilobite, and the sea bed over which it travels will someday be Toronto. The creature passes corals and sea stars, while minuscule worm-like vertebrates—so-called conodont animals—swim by overhead. Nearby sea lilies reach for passing food with their feathery arms, like starfish laying on their backs, tethered to the sea floor on long stems. The world is already ancient. A hundred million years earlier, the Cambrian explosion—a period of intense biological diversification—produced the ancestors of almost all the animals alive today. Two billion years before that, photosynthesizing bacteria began releasing oxygen into the planet’s previously unbreathable atmosphere. And another two billion years back, an object the size of Mars floated into our solar system, crashed into a nascent earth, shattered, and reformed as our moon. When this trilobite was alive—450 million years ago, late in the Paleozoic era’s Ordovician period—the world was a very different place. The sun rose and set on some 390 shortened earth days each year. There was no polar ice, and water from the oceans flooded across the land, pooling into shallow seas. North America was part of a supercontinent called Laurentia, and present-day Toronto sat 10 or 20 degrees below the equator. Trilobites were plentiful here then, and their fossils have regularly turned up in exposed Ordovician rock by the Humber River, Etobicoke Creek, and Don Valley Brick Works. Some 5,000 different genera of the invertebrate—which belonged to a group of still-thriving organisms called arthropods—have been identified. One of the trilobites most commonly found in Toronto, known as Isotelus, was among the largest to have existed, sometimes reaching 30 centimetres in length. That's a really big trilobite since Typically, an adult trilobite is a few centimetres long. You can hold it in the palm of your hand. For more information about fossils and trilobites in the Toronto area visit http://torontoist.com/2012/03/prehistoric- toronto-the-paleozoic-era/

LOGGING REQUIREMENTS:

TO LOG THIS EARTHCACHE, YOU MUST COMPLETE THE FOLLOWING

1. Go to waypoint 1 and waypoint 2 (shows waypoint just below) and see if there is any differences between the fossils.  Email me yes or no.

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   2. Find a fossil and post a picture of the fossil you have found from both waypoints and include you and your GPS. (optional)

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   3. Find a fossil and email your best description of it.

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Most important : HAVE FUN!

Please do NOT take any fossils home with you as there should be many more for others to enjoy too.

Remember this is supposed to be fun!  Don't be too worried about getting the awnser super duper specific and fancy.

Thank you to the TRCA for giving permission for this Earthcache.

DO NOT PUT THE ANSWERS TO THE QUESTIONS IN YOUR LOG.

EMAIL THEM TO ME AT masageocache@gmail.com

Congrats to Carni for the FTF