Geological Time Scales: Evidence For
Evolution
NAME: SOLUTION
From your studies in ‘Are We Alone’ you should have learned that
many scientists believe life could exist on other planets in the
universe and that scientists have proposed a theory of how the
universe began, known as the 'Big Bang Theory'.
But how did life start on Earth and how do scientists explain the
changes in life forms that have occupied our planet over time?
Life on Earth
The scientific community is divided on the question of how exactly
life began on Earth. Two main theories are:
1. The basic chemical building blocks to make a living cell were
present on Earth. An energy source (eg a lightning strike) may
have provided the stimulus to convert these chemicals into amino
acids, the chemicals needed to make proteins for living systems.
2. Life originated from elsewhere in space, and the chemicals
needed to produce primitive living cells travelled to Earth on
comets or meteors.
Neither theory has enough evidence at present for the scientific
community to give a definitive, accepted answer to this question.
How life has changed on Earth
Even though science has not fully explained the origin of the first
living cell on earth, more scientific evidence is present to explain how
primitive life changed (or evolved) into complex living systems we
see on earth today.
As this change from primitive to complex organisms is often a very slow process, geological
timescales and the age of the Earth (around 4.6 billion years old) provides support for Darwin’s
theory of change via the process of natural selection.
Geological Time Scale
Geologists (scientists studying changes on Earth) and palaeontologists (who study fossils) have
developed a geological time scale, dividing the time they believe the earth has existed into periods.
Each period has special fossils associated with it. For example, main types of fossils found from the
Permian period are different to those found in the Triassic period. The end of most periods is
marked by a large number of extinctions. The most famous of these is the extinction of many plants
and animals, including dinosaurs, at the end of the Cretaceous Period.
All of the periods have been dated by a process carried out on fossils called radioactive dating.
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Watch the BRAINPOP "Geologic Time"
For You To Do
1.
The table below shows the time-line of the Earth if it has been condensed into one hour. On
the clock face below, label these events on it.
Forests of ferns and conifers cover
First mammals appear on Earth
the land
First flowers seen on Earth
First reptiles walk on land
First insects fly over Earth
Extinction of dinosaurs
First plants grow on land
First humans
First fish appear as fossils
Animals with hard shells common
Multicellular soft-bodied
animals abundant
Single celled
microscopic life
exists
Single celled life abundant, oxygen in atmosphere
2.
The diagram below is a geological time scale. Answer the questions which follow it.
Geological Time Scale: The Earth’s Eons, Eras and Periods
TRIASSIC
millions of
years ago
(a)
Rank these time intervals from longest to shortest: era, period and eon.
Eon (longest as many eras), era (many periods) and then period (shortest)
(b)
How many years did the Devonian period last for?
48 million years (as it began 408 mya and finished 360 mya).
(c)
What was the shortest period? Quaternary
(d)
(e)
Which period could be referred to as the:
(i)
age of fish?
Devonian
(ii)
age of reptiles?
(iii)
age of gymnosperms? Triassic
Rank in order of appearance in the geological record:
(i)
angiosperms, ferns, algae, gymnosperms
1. algae
2. ferns
3. gymnosperms
(ii)
(f)
Jurassic
4. angiosperms
fish, reptiles, birds, mammals, amphibians
1. fish 2. amphibians 3. reptiles
4. mammals and birds (close but mammals first)
On a separate sheet of paper, draw a time line below, 1 m long, with the scale 10 cm
= 500 million years. Mark on the line the start of each period (a geological time scale
is found on the following page). What main feature do you observe from the timeline?