December 20: The Cosmic Calendar and Land Plants

On Carl Sagan's Cosmic Calendar, where the history of the universe is condensed into a calendar year, the first land plants emerge around December 20th. Since we last checked in on the Cosmic calendar on December 5th, simple and then more complex animals had evolved including insects, fish and even

The Rainforest I Live In

early amphibians. But all of that diversity of life existed in the seas. The planet had been in existence for 3.5 billion years already, that's thirty five thousand million years, with almost nothing living on the land. The oxygen level in the atmosphere was very low and there was no ozone layer, making the terrestrial environments bathed in UV light that destroys living tissues. Right around 500 million years plants like mosses and lichens started to be seen in the shore line environments at the edge of coastal waters. They had probably been colonizing the intertidal zones and estuaries for a long time, evolving adaptations to survive being dried out by the sun and the wind. Then, 425 million years ago in the Silurian Period, a totally new kind of plant evolved. These plants had special structures that helped them manage and transport water in their tissues like xylem and waxy coverings on their leaves and stems.

Spring in Portland

With these new pioneers the whole of the Earth's surface was opened up to colonization by the animals that ate plants and in turn by the animals that ate other animals. We are terrestrial creatures who would not have evolved, all those hundreds of millions of years later, if it were not for the amazing advances in water management devised by these early plants.

I live in an ecosystem dominated by large plants. Parts of Western Oregon are actually designated temperate rainforests and all of it is heavily covered in trees, grasses, ferns, shrubs and weedy herbs. My mother, who grew up in Southern California, still sometimes complains about "all this damn green!" At times you literally can not see the forest for the trees where I live. As a teenager I had an epiphany moment in a forest near my house when I gazed up at a young alder tree next to a creek and really processed what my science teacher had been lecturing about xylem, phloem and water transport in trees. This tree is moving water dozens of feet, and that one over there hundreds of feet, with simply water tension, evaporation and magic! It blew my mind then, and it blows my mind now. It blows Derek Mueller's mind too so he made this amazing video to tell us why trees can get so tall. Enjoy!

What blows your mind about plants, or about anything else outside? What is your favorite plant? Spend a moment to thank a vascular plant today, we depend on them for a lot.