Earth Science

Life on Earth

Evolution of Simple Cells

Study Tip

To remember the difference between eukaryotes and prokaryotes, remember that YOU are a eukaryote. You are a larger, more advanced organism whose eukaryotic cells have nuclei.

Organic Molecules

Organic molecules were formed from proteins and nucleic acids. They became complex by binding with clay minerals. Clay catalyzed the molecules to form polymers, some of which became RNA fragments. Organic molecules become cells when they separate from its environment via lipid membranes.

Study Tip

To remember the difference between eukaryotes and prokaryotes, remember that YOU are a eukaryote. You are a larger, more advanced organism whose eukaryotic cells have nuclei.

Prokaryotes

The earliest cells were prokaryotes, lacking a nucleus and other membrane-bound organelles. LUCA, the Last Universal Common Ancestor, lived 3.5 to 3.8 billion years ago. All current living organisms can be traced back to LUCA. Luca’s genetic code was based on DNA.

LUCA: The last universal common ancestor

In this photo, photosynthesis occurs in a leaf, which takes in carbon dioxide and releases oxygen and water.

Photosynthesis

The first organisms absorbed nutrients around them. When photosynthesis started 3 billion years ago, it allowed organisms to use sunlight and inorganic molecules (such as carbon dioxide and water) to create chemical energy to use as food. Photosynthesis requires that cells have chloroplasts. Importance of photosynthesis:

Allowed organisms to create food energy themselves
Oxygen was produced, which allowed aerobic organisms to evolve

Earth Science

Cyanobacteria

First present 2.8 billion years ago, Cyanobacteria are the oldest known fossils from organisms. Because they are known to be one of the first organisms to photosynthesize, Earth changed from an anaerobic to an aerobic environment. Cyanobacteria lived in reef like structures called stromatolites. Cyanobacteria can exist as blue-green algae and are found in various environments even today.

Concept Check

What did all current living organisms evolve from?
What important feature did simple cells evolve to include, and how does this help them survive independently?