Science Book report
Joe Schumaker
A. Lost Creatures of the Earth: Mass Extinction in the History of Life
B. Jon Erickson
C. Facts On File. Inc.; 132 West 31st Street, New York, NY, 10001
D. 2001
E. 265 pgs.
F. 10 Chps.
G. Chapter One: The Ages of Life
The chapter goes over life’s evolution in a geologic scale, from its beginning to now. The
Precambrian era lasted 4 Billion years and made up all but a tenth of life’s existence on earth.
The next era, the Paleozoic, a half-billion years ago to little under three hundred million, was a
time of major change in life and the first land creatures evolved. Then came the Mesozoic, from
a quarter-billion years ago to the extinction that gave rise to mammal rule, was dominated by the
Dinosaurs. The last era, the Cenozoic, has been ruled primarily by mammals, with birds taking
up entirely new niches in the ecosystems. Life in the Precambrian was mainly bacteria and algae,
with algae fossilizing in layers. Most of life existed without real complexity till photosynthesis
changed everything. Algae produced immense amounts of oxygen, resulting in other life-forms
becoming dependent on algae for food and oxygen. Life went through several stages, starting
with worm like creatures, moving on to lobsters and crabs and their other relatives. Next came
the domination of fish, then amphibians crawled out onto land to claim their bounty of plants.
From them came reptiles, who led to dinosaurs, with mammals now dominating the planet.
Chapter Two: Sea Life
The Protozoan’s were the first animals that existed throughout most of earth existence. The first
kinds were protists, which had nucleuses. The majority of protists did not fossilize well since
they were soft and had no hard remains. 600 million years ago, the first multi-cellular animals
called metazoans evolved. Sponges were some of the first and most successful metazoans. Next
came jellyfish, which were a little more advanced than sponges. Eventually, shelled creatures
came along, still without spines. About 520 million years ago, the first jawed creatures began to
evolve, leading to fish like animals, with spines, and were able to grow and move more
effectively than invertebrates. Eventually, jawed fish dominated the seas and climbed to the top
of the food chain. About 20 million years ago, dolphins reached their current intelligence, along
with other Cetaceans. Whales and their relatives evolved from ungulates, creatures with hoofed
feat. They beat sharks and fish in diving and swimming and all around eating.
Chapter Three: Land life
The first life to venture out of the seas was plants, only needing light and water to survive. The
first of those were mosses and lichens. They eventually gave rise to gymnosperms, which
resulted in club mosses, and most of today’s modern plants. Plants called lycopods were the
dominant type in ancient swamps, with their branches growing a spiral. Many plants in the
swamps remained unbeaten when they died and formed massive amounts of coal after
fossilization. True ferns became widespread through the Mesozoic and became a staple food for
dinosaurs. Eventually, amphibians crawled upon the land and began a rapid expansion. Reptiles
first evolved just 300 million years ago to dominate the land. They even spread into the sea and
air. With narrower tracks and longer steps, they could easily run down their prey. Their scales
allowed them to keep their fluids in and meant the animal only needed to drink water and not live
in it. Eventually, mammal like reptiles evolved and showed improvements over their
predecessors. With better body temperature control and fur, they were able to keep more of their
energy, lessening the food needed for their active lifestyles. The dinosaurs took over before
mammals could fully evolve, and they reigned over the earth for millions of years, producing a
wide variety of creatures of all shapes and sizes. Small dinosaurs eventually evolved into
primitive birds, and took to the skies. After the extinction of dinosaurs, mammals grew in size
and rapidly proceeded to where they are today.
Chapter Four: Mass Extinctions
Earth has suffered dozens of extinctions throughout history, though some of them stand
out more than others. One of the first great ones was the Precambrian Extinction, when algae
decreased in diversity. At the same time, the first worm like animals evolved to eat the algae.
About 850 million years ago, ice ages repeatedly occurred for the next 200 million years, killing
many of the primitive creatures in the oceans. Then volcanoes erupted, sending carbon dioxide
into the atmosphere, creating a greenhouse effect. Life was then able to spread and develop. At
the time, there was one big supercontinent, named Rodinia. Eventually, animals began to take
use of oxygen to allow them support larger bodies, and greater activity. Unfortunately, many
species became too restricted and unable to evolve to meet rapidly changing environments, and a
massive extinction occurred. At the time of the Cambrian period, life had reached an all time
high in diversity and suffered huge extinctions. During the Ordovician, the planet began to freeze
as plants started climbing onto the land, though they, and animals, were in abundance among
reefs. By the time of the Triassic, all primitive forms of amphibians had gone extinct, pushed out
by other species, with many reptiles, mammal like creatures and thecodonts dominating the land.
Once the Jurassic came, Dinosaurs were the dominate creatures on a supercontinent that was
splitting apart. At around 100 million years ago, several dominant dinosaurs’ species went
extinct, being replaced by species from Eurasia. Sauropods were extinct and their places were
taken by duck-bills, and horned dinosaurs. During the Cretaceous dinosaurs thrived in the warm
climate, but went extinct at the end of the era. Cephalopods also became extinct, except for the
lonely nautilus. Another 8 million years later, the sea suffered its own extinction of bottom
feeders. Now mammals began to grow, becoming grazers and predators akin to the dinosaurs,
though not of the same size. At the end of the Eocene epoch, temperatures across the world
dropped, killing off many primitive mammals. After the extinction, mammals evolved to share
the traits we know today. At the same time of the extinction, Greenland separated from North
America, letting cold water into the Atlantic, lowering ocean temperature, and causing
Antarctica’s ice sheet to grow. Also, Alaska sometimes became connected to Siberia through the
Bering Strait, preventing the ice from receiving warm currents, causing it to grow. About 3
million years ago, the Isthmus of Panama connected North and South America, allowing species
from both to spread to the other. Over the last few ten-thousand years, almost all mega-fauna
went extinct, coinciding with humans’ ascent to intelligence.
Chapter Five: Causes of Extinction
Geological cycles are typically the best explanation for extinctions, with the movement of the
continents causing continual changes across the globe. There are also cosmic events, such as
stars going supernova. Also, the last two major extinctions occurred when the solar system
reached the edge of the galactic plane. Evidence points to the extinction of the dinosaurs
occurring at this time. It might be that the Earth receives large amounts of radiation when it
reaches these points, affecting the environment. Another theory is Geomagnetic Reversal, where
the Earth’s magnetic field switches its polarity. Reversals may also have been the causes of ice
ages in the past. There is no specific pattern for when Geomagnetic Reversals occur, with the last
170 million years having experienced 300 reversals, with the latest being 780 thousand years
ago. Long valley in California experienced basalt floods, and a meteorite impacted Australia at
this time. The evidence suggests that we are overdue for a reversal. Cometary impacts are
another possible cause of extinction. However they are far rarer than asteroids, which are a great
deal more likely to cause extinctions. It’s not known how they break their orbits, but their
impacts are tremendously powerful, leaving immense craters. When one impacts on Earth, it
flings dirt and rock into the atmosphere, preventing light from getting through. Volcanic
eruptions hurl tons of gasses such as sulfur, as well as ash. Volcanism is often caused by
continental drift. Continental drift also changes the temperature of environments, forcing species
to adapt to new weather conditions.
Chapter Six: Effects of Extinction
When extinctions do occur, they always result in major changes in ecosystems. Nearly
every species that has ever evolved is now extinct, evolving into extinction or dying out. Species
regularly form and die on a geologic time scale, with extinctions setting life back several million
years in evolution. Usually, extinctions occur when the climate changes too rapidly for animals
to adapt, killing them off. Most of the types of plants and animals that live now evolved over the
past 600 million years. Also, while there are large extinctions, there are often smaller extinctions,
wiping out a few dozen species at a time. When species survive extinctions, it’s often because
they are more adaptable, and able to survive in more environments. In addition, when species die
out, other species evolve and diverge to take the niches of the extinct species. Also, while some
species will adapt similar qualities to extinct species, they can never recreate the exact DNA
combinations, meaning that when a species goes extinct, it is gone forever.
Chapter Seven: The Evolution of species
When species evolve, they either evolve better adaptions for their niche, or evolve to take
a new niche. The ocean has the greatest diversity of animals of any place on the planet, since
land has a more limited capacity. Most marine life is centered on reefs and continental shelves
and islands. Shallows tend to affect their species more than ecosystems further out at sea. Coral
reefs support more life than any other ecosystem, with plants taking advantage of corals ability to
build wave-breakers. Corals are large groups of algae that build gigantic frameworks, where fish
and other creatures can hide from predators. Species vary by the oceans they live in, since there
is not much of a way for species to migrate across land-bridges, but species still have similar
traits in similar environments. Animal species can diverge relatively quickly, yet stay similar,
like the finches of the Galapagos islands.