Origin and Evolution of Life
Everything began. Pre- Cambrian: It started about 4.6 billion years
ago. The Earth was formed in the beginning of this era. The air was
very toxic. The first one-celled living beings appeared, and then multicelled and more complex beings. They lived in water.
Paleozoic: It was a time of great changes in the planet and it is subdivided
in six periods:
• Cambrian: First shellfish, primitive fish, corals, algae and mollusks
were dominant in the oceans.
• Ordovician: First land plants and initial fish appeared.
• Silurian: First insects emerged and more plants were on land.
• Devonian: The first sharks appeared, as well as bony fish.
Amphibians and spiders and the first terrestrial forests started
colonizing land.
• Carboniferous: The first reptiles and insects with wings appeared
on land.
• Permian: Diverse animal and plant life appeared, reptiles
diversified. Then there was a mass extinction.
O Oxygen was not always
present on our planet as
it is now. In the beginning,
toxic gases were all around
and some primitive bacteria
lived and developed in
that environment. Ancient
cyanobacteria appeared
and released oxygen into
the environment for
so long and formed the
atmosphere. This caused
other primitive bacteria
to die. It was the beginning
of photosynthesis.
Answer True (T) or False (F) according to the information in the reading.
If the sentence is false, correct it to make it true.
• The environment in the Pre-Cambrian Era had oxygen
at the beginning.
• The first living things that appeared were cyanobacteria.
• Amphibians appeared before fish.
• Plants first emerged in water.
• The first fish appeared during the Devonian period.
Everything began. Pre- Cambrian: It started about 4.6 billion years
ago. The Earth was formed in the beginning of this era. The air was
very toxic. The first one-celled living beings appeared, and then multicelled and more complex beings. They lived in water.
Paleozoic: It was a time of great changes in the planet and it is subdivided
in six periods:
• Cambrian: First shellfish, primitive fish, corals, algae and mollusks
were dominant in the oceans.
• Ordovician: First land plants and initial fish appeared.
• Silurian: First insects emerged and more plants were on land.
• Devonian: The first sharks appeared, as well as bony fish.
Amphibians and spiders and the first terrestrial forests started
colonizing land.
• Carboniferous: The first reptiles and insects with wings appeared
on land.
• Permian: Diverse animal and plant life appeared, reptiles
diversified. Then there was a mass extinction.
O Oxygen was not always
present on our planet as
it is now. In the beginning,
toxic gases were all around
and some primitive bacteria
lived and developed in
that environment. Ancient
cyanobacteria appeared
and released oxygen into
the environment for
so long and formed the
atmosphere. This caused
other primitive bacteria
to die. It was the beginning
of photosynthesis.
Answer True (T) or False (F) according to the information in the reading.
If the sentence is false, correct it to make it true.
• The environment in the Pre-Cambrian Era had oxygen
at the beginning.
• The first living things that appeared were cyanobacteria.
• Amphibians appeared before fish.
• Plants first emerged in water.
• The first fish appeared during the Devonian period.
Respuesta:
The environment in the Precambrian Era had false oxygen at first
The first living things that appeared
it was cyanobacteria. true
Amphibians appeared before false fish
Plants first emerged in water. true
The first fish appeared during the Devonian period. true