These are the most frequently used words in this book.
age
ago
air
along
although
amphibians
animals
another
areas
atmosphere
bacteria
believe
between
birds
body
called
cells
century
certain
changes
classification
current
dinosaurs
discovered
discoveries
disease
during
early
earth
earthquakes
even
events
evolution
example
extinction
first
fish
form
fossils
found
fungi
group
history
humans
idea
include
ing
kilometers
known
land
large
layer
life
major
mass
may
miles
million
modern
moon
mountains
mya
natural
new
north
number
ocean
order
organisms
part
period
planet
plants
reptiles
rock
scale
scientists
sea
solar
species
states
still
structures
studies
sun
surface
system
terms
theory
thought
time
today
two
use
used
water
waves
winds
world
years