​Objectives of the Lesson

1. ​identify the sequence of events of the history of life on earth;

2. name the pieces of evidence on the evolution of life on earth; and

3. recognize the importance of knowing the history of life on earth.

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​Timeline of Appearance of Life Forms

​4.6 - 3.8 BYA

​The early earth is said to be violent because of the meteorites and volcanic eruptions. With this condition, zircon crystal was formed.

​3.5 BYA

Scientists discovered what they thought were 3.5 billion-year-old fossils in western Australia almost 40 years ago. A new study reveals that these rocks did indeed contain organic life — making them the oldest fossils ever found. The finding confirms that Earth was home to microbial organisms 3.5 billions years ago.

​Stromatolites are the oldest known fossils, known as microfossils representing the beginning of life on Earth.

​3.0 BYA

The first photosynthetic organisms thrived on the earth which is blue-green algae called cyanobacteria. This allowed The Great Oxidation Event: the Earth's atmosphere gets oxygen.

​2.0 BYA

​Appearance of the first eukaryotes and the influx of multicellular organisms occurred 1.2 billion years ago.

​Eukaryotes are organisms having true nucleus. The DNA is enclosed within the nucleus whereas DNA of most prokaryotes lies enclosed in the cell’s cytoplasm. The first eukaryotes were protists.

​500 mya

Life on Earth exploded in diversity and form, and in a geological instant a number of new species flourished. This happened during the Paleozoic era when the trilobites and cephalopods became dominant in the ocean particularly during the Cambrian and Ordovician.

​251-65.5 MYA

Age of the Reptiles and are subdivided into three periods: Triassic, Jurassic, and Cretaceous Periods.

65.5 million years ago to the present

Cenozoic Era "Age of Mammals"

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​During this era, plants and animals look most like those on Earth today.

For life to evolve from simple single-celled organisms to many millions of species of prokaryotic species to simple eukaryotic species to all the protists, fungi, plants, and animals, took some time. The first life forms were very basic and this then allowed for the evolution of more complex life forms. Eukaryotic cells evolved from prokaryotic cells. The evolution of life is brought about the changes in the environment which are linked to changes in climate and geology. These Earth’s environmental changes made the Earth’s environment more suitable for a wider variety of life forms.