So finally we have a way for life to be itself. The barrier, the semi-permeable membrane found in all organisms, finally allowed for the development of a new environment separate from the chaos outside.
Let's take a closer look at how this barrier interacts with the environment in order to see how the principles of Successful Adaptation apply from point zero to point human billions of years later.
We know that the electrochemical properties of atoms and molecules can attract and repel other atoms and molecules, but there is a more basic interaction with the environment that we need to consider as well.
The physical geometry of the cell-membrane, it's 3-D structure in space also acts as a physical gate - allowing smaller molecules to pass through to the new environment while preventing larger molecules from accessing the inside.
This gate-keeper role of the membrane is essential to life. Letting positive elements in, keeping negative components out and getting rid of negative components as well as lock and key relationships are some of the key ways that a cell membrane interacts with the surrounding environment.
While we understand the electrochemical relationship between elements in the environment, the cell membrane forces us to also consider three-dimensional mechanics.
We can all see in our mind's eye that 2-foot square block will not fit into a 1-foot square hole. This is a physical limitation brought on by the 3-dimensional structure of space. In the same way there are holes on the surface of membranes that prevent molecules and atoms from breaching the membrane through to the tasty and delicious core.
We can now understand that physical geometry is an important part of our interaction with the environment right from the start of life on Earth. The physical aspects of objects are a necessary component to sensing and manipulating the environment.
There are three or four basic ways a single-cell creature can move, or not move through the environment: stationary, unmoving; drift freely within the environment; using a propeller/tail based propulsion; amoeboid crawling/oozing out pseudopodia.
Let's take a mythical stationary organism - for instance a single-cell organism that is attached to a rock. Even with a so-called stationary object, movement of the environment occurs around it - bad news if you're stuck in a cranny or crevasse and needed nutrients swish by oh-so-close, yet too far away to be of any good to you.
Similarly an organism that just drifts freely in the environment may have more opportunities to bump into required nutrition than a stationary organism, but it also has more opportunities to drift into a dangerous, toxic environment and it still would have no guarantee of finding food or safe haven.
Unsurprisingly, those first two categories of organisms are found in nature in plant evolution with phytoplankton exhibiting drifting and flagellar movement. Eventhough multicellular plants may seem stationary, they move toward their food sources - light from the Sun and water from soil - using branches, leaves and roots.
Though they can control their internal environment to an extent, there are limited ways for them to control their interaction with the greater environment. They do not exhibit as many opportunities for environmental interaction as more mobile life does.
Organisms that can move in the environment not only control their own internal environment, but also where they as creatures can exist within the environment - clearly superior to the previous categories and in accord with the principle of Successful Adaptation
Looking at the two ways that single-cell organisms direct themselves using flagellar/cilia and pseudopodia movements within the environment we can see the importance of how they would have more chances to find food, evade danger and find novel ways/places to interact with the environment around them.
Now that we can see how a barrier can form and then create a new environment, let's look at how typical microbes interact with the environment.
Another essential element in the establishment and evolution of life on Earth is adhesion. It is a vital interaction with the environment for all organisms and thankfully it is considered important enough to study seriously.
It's one thing to have a semi-permeable barrier allowing environmental interactions, but being able to move in the environment allows for more meaningful interactions with the environment. It allows for more opportunities for organisms to differentiate themselves from their peers and display successful adaptation.
Indeed, it is often thought that multicellular organisms arose not from an ability to move around the environment freely, but as a way to move the environment around themselves, thus creating a Successful Adaptation for their colony.