Living Environment Translated Arabic 2014 | Page 94

11. The Theory of Uniformitarianism states that every rock layer
was formed by the uniform laying down of sediment.
12.Scientists learn about past life by studying fossils.
a. The relative date of a fossil can be estimated from the
ages of rocks in nearby layers.
b. Radiometric dating that uses radioactive elements gives
more accurate dates for fossils.
c. The fossil record has gaps which may yet be filled with
later discoveries.
13.Evidence of evolutionary relationships can be shown by:
a. Homologous structures- body part that is similar in
structure on different organisms but performs different
functions. ( EX: forelimbs of bats, humans and moles have
the same bones in relation to each other
b. Analogous structures- structures that perform a similar
function but are not similar in origin. These structures
evolved separately are show that there was NOT a common
ancestor. (Ex: a bat’s wing has bones but an insect’s wing
does not)
c. Embryology – similar structures are present as the embryo
is developing. These structures may disappear before the
fetus is born. ( Ex: gill slits in humans)
d. Vestigial structures- structures that do not seem to have a
function and may once have functioned in the body of an
ancestor. (Ex: appendix in humans)
e. DNA comparisons- the similarities of nucleic acids in
organisms
f. The evolution of antibiotic-resistant bacteria, pesticideresistant insects, and rapid g