Week 3
On the third week, we learned about the evolution of life and we analyzed the timeline from the birth of the planet untill the first cell formed on our planet. From here, I learned that the history of life on Earth began about 3.8 billion years ago, initially with single-celled prokaryotic cells, such as bacteria. The first known single-celled organisms appeared on Earth about 3.5 billion years ago, roughly a billion years after Earth formed.
More complex forms of life took longer to evolve, with the first multicellular animals not appearing until about 600 million years ago. For the next 1.3 billion years (3.8 to 2.5 billion years ago), the Archean Period, first life began to appear and the world's landmasses began to form. Earth's initial life forms were bacteria, which could survive in the highly toxic atmosphere that existed during this time.
The first living things on Earth, single-celled micro-organisms or microbes lacking a cell nucleus or cell membrane known as prokaryotes, seem to have first appeared on Earth almost four billion years ago, just a few hundred million years after the formation of the Earth itself.
Then, around 2 billion years ago, Eukaryotic cells which are cells with internal “organs” (known as organelles) – come into being. One key organelle is the nucleus: the control centre of the cell, in which the genes are stored in the form of DNA.Eukaryotic cells evolved when one simple cell engulfed another, and the two lived together, more or less amicably – an example of “endosymbiosis”. The engulfed bacteria eventually become mitochondria, which provide eukaryotic cells with energy. The last common ancestor of all eukaryotic cells had mitochondria and had also developed sexual reproduction.
Later, eukaryotic cells engulfed photosynthetic bacteria and formed a symbiotic relationship with them. The engulfed bacteria evolved into chloroplasts; the organelles that give green plants their colour and allow them to extract energy from sunlight.Different lineages of eukaryotic cells acquired chloroplasts in this way on at least three separate occasions, and one of the resulting cell lines went on to evolve into all green algae and green plants.
More complex forms of life took longer to evolve, with the first multicellular animals not appearing until about 600 million years ago. For the next 1.3 billion years (3.8 to 2.5 billion years ago), the Archean Period, first life began to appear and the world's landmasses began to form. Earth's initial life forms were bacteria, which could survive in the highly toxic atmosphere that existed during this time.
The first living things on Earth, single-celled micro-organisms or microbes lacking a cell nucleus or cell membrane known as prokaryotes, seem to have first appeared on Earth almost four billion years ago, just a few hundred million years after the formation of the Earth itself.
Then, around 2 billion years ago, Eukaryotic cells which are cells with internal “organs” (known as organelles) – come into being. One key organelle is the nucleus: the control centre of the cell, in which the genes are stored in the form of DNA.Eukaryotic cells evolved when one simple cell engulfed another, and the two lived together, more or less amicably – an example of “endosymbiosis”. The engulfed bacteria eventually become mitochondria, which provide eukaryotic cells with energy. The last common ancestor of all eukaryotic cells had mitochondria and had also developed sexual reproduction.
Later, eukaryotic cells engulfed photosynthetic bacteria and formed a symbiotic relationship with them. The engulfed bacteria evolved into chloroplasts; the organelles that give green plants their colour and allow them to extract energy from sunlight.Different lineages of eukaryotic cells acquired chloroplasts in this way on at least three separate occasions, and one of the resulting cell lines went on to evolve into all green algae and green plants.
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