Bio1152
Chapter
25
The History of Life on Earth
A major tool biologists use to study early life on earth is the fossil record buried in
layers
of
rock called
.
The 4.6 billion years of earth's history is divided into three
geologic
, which are further divided into
,
, and
.
Most of the major animal
phyla
appeared during the early
period in what is known as the
Explosion.
Mammals are
synapsids
that belong to the group of vertebrates called
.
The
movement
of the Earth's
due to
continental
has shaped the diversity of life on Earth.
Animation.
There have been several episodes of
mass
, but the extinct forms were replaced by others that evolved from the survivors; the trend has been an
of diversity over time.
The
(PT)
extinction
was the most severe, and claimed over 90% of marine species.
The
(KT)
extinction
is famous for the
disappearance
of
(except birds).
The extinction of the dinosaurs may have led to the
radiation of other species, such as
mammals,
which diversified to adapt to new
now made
available.
Bio1152
Chapter
26
Phylogeny and The Tree of Life
is the study of the evolutionary history and relationships of
organisms,
based on shared
characters inherited from a common
.
Carolus
Linnaeus
introduced a system of
, for classifying species in seven
hierarchical
categories (taxa).
Phylogenetic
relationships
are shown as branching trees where each
branch
point represents the
of two
when they shared a common
(homology).
similarity can be misleading due to
evolution
(analogy).
homologies that make use of computer programs to analyze
segments
can reveal many relationships not attainable by other methods.
Shared ancestry and shared
characters
are drawn on a
to show evolutionary
relationships;
this practice is called
.
A clade must be
, and consists of the
species and all its
descendants;
The tree of
life
is divided into three great clades called
:
(Monera),
, and
.