Kirk R. Johnson - Cruisin the Fossil Coastline

Text 2018 Kirk Johnson

Illustrations 2018 Ray Troll

Photos 20102018 Kirk Johnson and Ray Troll

All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise without written permission from the publisher.

Library of Congress Cataloging-in-Publication Data

Names: Johnson, Kirk R., 1960- author. | Troll, Ray, 1954- illustrator.

Title: Cruisin the fossil coastline : the travels of an artist and a scientist along the shores of the prehistoric pacific / written by Kirk Johnson ; illustrated by Ray Troll.

Description: Golden, CO : Fulcrum Publishing, [2018] | Audience: Age 12+ | Audience: Grade 7 to 8. | Includes index.

Identifiers: LCCN 2018013103 | ISBN 9781555917432

Subjects: LCSH: Fossils--Pacific Coast (North America)--Juvenile literature.

Classification: LCC QE714.5 .J634 2018 | DDC 560.979--dc23

LC record available at https://lccn.loc.gov/2018013103

Project Manager: Rebecca McEwen

Editor: Alison Auch

Digital color by: Grace Freeman: IV-V, VII, X, 5, 6, 9, 21, 33, 36-37, 43, 49, 56-57, 76-77, 83, 84, 90, 96, 101, 109, 123, 142, 147, 148, 161, 162-163, 170-171, 182-183, 184-185, 209, 210-211, 212-213, 214, 218, 231 (bottom), 232-233, 245, 246; Ray Troll and Memo Juaregui collaborative acrylic mural VI-VII; Memo Juaregui: XII-1, 2-3, 118-119; Terry Pyles: 116-117

Printed in South Korea

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Fulcrum Publishing

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Golden, CO 80403

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FOR CHASE, PAST AND FUTURE.

K. J.

FOR MY IRISH TWIN SISTER MIMI AND FOR SEAN DURAN WHOSE FRIENDSHIP AND WISDOM TOUCHED SO MANY.

R. T.

The curious thing about the West Coast of North America is that it has been a coast for a very long time. That statement seems obvious, and perhaps not even worth stating, but it turns out to be true, even when viewed from the inky depths of geologic time. This coastline has been around for more than 750 million years.

Helicoprion, also known as the buzz saw or whorl-toothed shark, lived during the Permian Period and roamed the shores of western North America.

On Earth, coastlines come and coastlines go. They do this through the slow but steady process of plate tectonics. Over the long history of the planet, continents split and pull apart, forming half-continents that face each other and then slowly recede from each others view. The Atlantic Ocean was formed by this process. Two hundred million years ago, the Atlantic wasnt even wet it was the place where North and South America were stuck to Europe and Africa. But once the split occurred, a narrow sea formed, eventually widening to become an ocean that is still getting wider today. And when the Atlantic formed, it had two coasts that had not been there before.

As for those coastlines that go away? Consider this: Before India collided with Asia about 40 million years ago, it had a north coast and Asia had a south coast. Those coasts were then smashed together and thrust into the sky, forming the Himalayas, the worlds highest mountain range. Two coasts became one mountain range.

Mountains are often found along coasts, and this is no coincidence. Mountains are formed when the rock at the deep bottom of an ocean is pushed into a continent. The deep ocean rock is more dense than the rocks of the continent, so the ocean floor is driven below the continent. This drags the edge of the continent down into the Earth where it heats up and eventually melts, forming liquid rock known as magma. Some of this liquid rock, full of gas like a carbonated beverage, squirts up through cracks and erupts at the surface, forming volcanoes and lava flows.

Coastal mountains also form when chains of ocean islands are carried into slow motion collisions with continents. Rather than sliding under the continents, the island chains become welded to them, adding land and growing the continent at the expense of the ocean. This means that the Pacific Coast has been growing to the West, and older versions of it can be found in places such as Nevada and Idaho. Like many of us, North America has grown wider as it has grown older.

It is not just the edge of the continent that is being modified, though. Sea level rises when melting ice sheets make more seawater or when the eruption of seafloor volcanoes decrease the volume of the ocean basin. It falls when ice sheets form or when seafloor volcanic activity slows down. A rising sea level will flood the coast, turning river valleys into estuaries and pushing beaches onto the shore. A falling sea level will expose old seafloor to the air and allow forests to colonize what used to be kelp beds.

When you combine all of these things, the result is that the relationship of the continent with its adjacent ocean is always changing. For as long as a coast exists, its mountains, hills, headlands, rivers, estuaries, bays, and beaches will slowly change their shape even their location because they are at the mercy of relentlessly moving geologic plates and an ever-changing sea level.

And while all of this geology is going on, climate changes, ecosystems form and disband, plants and animals live and die, and species evolve and become extinct. Fortunately, one of the most archival features of our planet is that it buries its dead (at least some of them). Animals and plants (or parts of them) occasionally get buried in sand or mud or lava or tar and become fossils. And because the coast is always moving up or down, and because the sea level is always moving up or down, and because the coastline is always eroding or depositing, fossils are continually being formed, deposited, uplifted, exposed, and eroded along coastlines. Coastlines are fabulous places to find fossils.

As one of the longest-lived coasts on Earth, the West Coast has seen a span of time that fully encompasses the evolution of complex life. Yet despite its great antiquity, it is still a geologically active place with coastal mountain ranges, raging rivers, earthquakes, faults, subduction zones, submarine canyons, volcanoes, landslides, and tsunamis. The northern section of the coast is home to endless fjords, huge ice sheets, sea ice, and mountain glaciers. This eternal coastline has been a stage for the evolution and extinction of myriad coastal animals, plants, and ecosystems. Put another way, this place has seen millions of variations on the theme of surf and turf over the last three-quarters of a billion years.