Cradle of Life: reading assignments. Chapter 1

A brief guide to the main concepts discussed in the first Chapter of "Cradle Of Life"

Chapter 1: DARWIN'S DILEMMA

For this first chapter, I am presenting a few sample questions from each of the paragraphs in the book. These questions should help you and guide you through the reading and also provide an indication of what kind of information you need to acquire. Some of these questions were actually asked in past quizzes and exams and might show up again in this upcoming quiz.

Breakthrough to the Ancient Past
- What kind of new knowledge concerning the earliest fossil record has been acquired in the last four decades?
  (your book actually says three decades but note that it was written in 1998/1999)
- When did Earth become livable?
- What relation exists between today's plants and animals, and microbial organisms that are millions of years old?
- Before this information became available, what was the big problem that even geologists of the mid-1800s were aware of?
- Charles Darwin's theory of Evolution by Natural Selection might have been undermined by this problem. Why was that?
The Nature of Geologic Time
MAIN CONCEPT: Geologic time is measured in billions of years. To better understand the deep meaning of these huge and apparently incomprehensible numbers, we need to understand how to subdivide this span of time. "Human" time can be subdivided in years, months, weeks, days, hours, minutes, seconds and so on, when we can use numbers; or it can simply be illustrated by a more or less regular sequence of events. For instance, in one day you would likely follow this routine: breakfast, classes, lunch, schoolwork, dinner, relax, bedtime, regardless of the precise instant in which they happen.
We will proceed with a similar approach when we study geologic time.
- How do we divide Geologic Time?
- What is the name of the two major Eons into which Geologic Time is divided?
  (remember that today we also divide the oldest of these two into the Proterozoic, the Archean, and the Hadean Eons)
- Why the name Precambrian? How is it related to the fossil record?
- What does the Law of Superposition say?
- Is the (sedimentary) rock record continuous or full of gaps? Why?
- Why are the sedimentary rocks that have been deposited on the ocean floor only 250 my old or younger?
- Why are fossils useful in the context of assigning an age to rocks?
- The end of the Paleozoic coincides with the extinction of trilobites, and the end of the Mesozoic coincides with the extinction of dinosaurs. Is this just a coincidence, or were the boundary of these eras chosen on purpose to match these extinctions?
The "Schoolbook" History of Life
MAIN CONCEPT: The history of the Phanerozoic, the Eon with which we are the most familiar (from contemporary newspapers, magazines, movies, etc.), spans only 1/8 of Earth's history
- Can you think of one or more reasons why we humans tended to have a shortsighted view of both life's long history and of the relevance of the Precambrian?
- After reading the pages of this section, can you think of some fundamental questions, the answers to which lie in the understanding of the Precambrian evolutionary history?
Darwin's Dilemma
MAIN CONCEPT: Science is made by human beings. Their personalities, status and social settings impact their search for knowledge
- What was troubling Charles Darwin?
- John William Dawson and the infamous Eozoon Canadense:
  - Hindrance or help?
  - Did he find an answer to Darwin's Dilemma?
- Who was Charles Doolittle Walcott, and what were his major contributions to the field?
- Who were James Hall and John Wesley Powell, and what did they do?
- What is the Cryptozoon controversy?
- What extremely important discovery was made in 1909 by Walcott near Burgess Pass, in the Canadian Rockies?
- Percy Raymond and Albert Charles Seward: was their criticism of Walcott's discoveries and ideas a contribution to the advancement of science, or rather a disservice? How so?
A stromatolite from the Logan Pass area, Glacier National Park, Montana
(see coin to the left for scale)
© Alessandro Grippo, 2010

The same image, with a rough outline of the profile of the stromatolite.
© Alessandro Grippo, 2010
The area of Glacier National Park where this picture was taken coincides with the area where
C. D. Walcott "reported many types of Cryptozoon-like structures" (see page 28 of Cradle of Life)
Denouement
- Who were the main characters involved in the search for the missing Precambrian life?
- Can you summarize their main contribution to this search, whether positive or negative?

Go back to Top | Go to the Images Page | Go back to the Home Page | Go back to the Cradle of Life Page