Levels by which we can view life

Put all these together and you get…..next on the list

Atomic – atoms – see periodic table of elements below

Molecular – atoms bind together to form molecules

Biochemical – molecules interact in chemical reactions and make us

Organelles – part of a cell where chemical reactions take place

Cell – all this taking place in a single cell - basic unit of life

Organs – group of cells functioning within a unit for a purpose

The whole living organism - in our case, human beings


Let’s keep this in mind and look at evolution of life on earth

Look at periodic table, look at carbon, the living atom, and other important elements in living organisms: Oxygen and Nitrogen to a large extent, with many of the other elements like chlorine, sodium, potassium, calcium and many others…

Life first emerged on the earth about 4 and 3.5 billion years ago, when certain molecules had developed that somehow reacted with each other to form a living thing that could reproduce itself.  Exactly what happened and how this happened is not known, but at some point in time it must have happened, because there is life on the planet and we are talking about it right now. These organisms developed into single celled organisms, now called prokaryotes, they are the simplest form of life and are bacteria and archaea (R key ah), which can live in extreme environments (in terms of temperature, salt content and/or pH), and are thought to be the closest to the first living cells that emerged 3.5 billion years ago:

The next step in evolution was the appearance of single celled eukaryotes 2.7 billion years ago.  These cells have a well defined nucleus which contain the DNA of the cell. They also have mitochondria and other organelles, an organelle being an “organ” with a particular purpose inside the cell.  Notice above that prokaryotes do not have a nucleus or organelles. Also note that mitochondria in eukaryotes contain different DNA then the nucleus of the cell, so what most likely happened here was a eukaryotic cell absorbed a prokaryotic cell that then became a critical part of that cell – the mitochondria – mitochondria provide chemical energy for the cell. Examples of single celled eukaryotes are protozoa, and species of algae that are single celled.


Algae structure and function

The DNA is like the architectural blueprint of the cell, it codes the information from which the cell creates itself, and how it functions and reproduces itself, the difference being, a blueprint has all the information to construct something, but the blueprint does construct or reproduce itself like a cell and a living organism does.

Multicellular eukaryotic organisms appeared on the planet about 1 billion years ago.  That’s when somehow single celled eukaryotic organisms figured out a way to be more productive, and more reproductive, if they merged together forming a multicellular organism.  Examples of eukaryotic organisms are brown, red, and green algae, fungus, plants and animals.

Let’s follow the evolution of eukaryotic organisms from their start 1 billion years ago.

Six hundred million years ago simple multicellular organisms (simple from our perspective, but the most complex at the time) similar to jellyfish and worms split evolutionarily into what would become two different groups of animals, vertbrates and invertebrates, as in fish/amphibians/reptiles/mammals and insects/spiders/crab/shrimp, etc…

The appearance of fish in the evolutionary record started about 500 million years ago primarily in the oceans of the earth.



The earliest amphibians evolved in the Devonian period 400 million years ago from fish with lungs and bony-limbed fins, features that were helpful in adapting to dry land. Amphibians lay their eggs in water, but can live on land.

400 million
years ago


Reptiles appeared on the evolutionary clock about 300 million years ago, they were the first animal species that could live completely on land.  Reptiles have scales, are cold blooded and lay their eggs on land. Dinosaurs comprised the largest group of reptiles and the largest animals that ever roamed the earth They became extinct 65 million years ago.  An asteroid is thought to have crashed into the earth in the area of the Yucatan peninsula in Mexico, which threw such a huge plume of ashes and debris into the air that it saturated the atmosphere for years, limiting the sun’s shine on the earth, killing almost all plants and thus causing the extinction of dinosaurs – they no longer had huge amounts of plants to eat.  A brachiosaurus would need to eat 1000 pounds of plants per day to survive.

Note that before the dinosaurs went extinct 65 million years ago, mammals were already present, as small nocturnal creatures:

The few mammals that existed 65 million years ago were mainly nocturnal insect eaters, and as such, they were able to survive the asteroid strike – there were still plenty of bugs around.

Here’s what happened evolutionarily after that:

Sixty million years ago, our ancestor went into the trees, and looked like lemurs today:

And then 50 million years ago split into tarsiers:

Then 35 million years ago into new world monkeys, now living in Mexico and South America:

Then 23 million years ago into old world monkeys, now living in Africa and Asia:

Then 14 million years ago into gibbons:

12 million years ago into orangutans:

8 million years ago into gorillas:

And 5 million years ago split into chimpanzees:

Which then leads us to 4 million years ago, and Australopithecus coming down from the trees:

Then to Homo habilis 3 Million years ago:

And to Homo erectus 2 million years ago

Then to Homo sapiens 300,000 years ago:

And Homo sapiens today

We can now see the stages of the evolution of life over resulting in the development of us as human beings as the dominant species on the planet.

Is anyone familiar with genes and genetics? That’s your DNA. Brainstorm here with the class about traits, genes, 23 and me, etc…

Now for a piece of anecdotal information, which I think can be quite philosophical.  Have you ever noticed that at all elementary schools and many parks, there are playscapes:

I have 3rd grade recess duty at the elementary school I work at. I’m out there with kids playing, they’re all over the playscape, swinging on swings, climbing walls, sliding down slides, crawling in tunnels. Anyone have any ideas why young kids might like playing like this on playscapes?

Because it’s still in our genes, it’s part of our history, we came down from the trees 4 million years ago, which is a snap in time on the evolutionary scale, and those historic traits get expressed in early childhood development, after which we developmentally grow out of it, most of us anyway:)

Does anybody recall climbing trees as a kid?  I recall the maple tree in my yard when I was 6 or 7 years old.  My grandfather put a rope ladder on a branch, and I would climb it on a regular basis.  I can still picture in my head my favorite place to sit, way up on the highest branch, where the branch split in three and made a perfect seat, with 2 branches sprouting out below to rest my feet on......  That's from whence we came..... It's in our genes.