The Greening of the Earth: Evolution of Plants (April 8-12)

Plants have been in this course for awhile as a leafy background to tetrapod evolution, but now it is time to take them seriously. The best place to start a general survey of our very distant green cousins is with the summary Tree of Life page on land plants (embryophytes). There are lots of links there. Berkeley’s fossil plants range chart may be especially useful, although we won’t be using most of the names given there. The most detailed plant website is the University of California on-line paleobotany lab. The diagrams and hierarchical systems of detail here are impressive. You may want to scan these pages for the beautiful line drawings alone.

Here’s a ginkgo webpage for everything you want to know about this beautiful tree common on our campus (although it is hardly the only “link between the lower and higher plants”). What is the tallest plant and where is it? A redwood in California measures an astonishing 379 feet.  Check out the oldest living plant — an impressive 13,000 years of life as a clone. It’s also in California. Here’s a short video of pollen stirred up by a helicopter in Georgia. Finally, a short video clip of stomata in action.

The evolution of angiosperms (flowering plants) is a bit contentious these days. Most paleontologists agree that the first definite angiosperm fossil is Cretaceous, but genetic and molecular studies suggest they evolved sometime in the Jurassic. There are disputes over what the fossil record really shows.

Now that you’ve accumulated quite a bit of life’s history, you might appreciate this deep-time clock. I can’t guarantee that all the dates will be correct, but the order of events is good. The main thing you will gain from this page is an appreciation for the scale of geologic time.

Exam #2 results: The average is 78%, with 5 scores in the 90s, 7 in the 80s, 11 in the 70s, 4 in the 60s, and 3 below 60. The range was 45-97%. Here are the Spring 2019 second test answers. (Each answer is from a different student. These are not optimal answers necessarily, but good enough for full credit.)

Merycoidodon skull, left side (Oligocene of Nebraska).

Geology in the News –

For the extraordinary story about the end-Cretaceous extinction deposits recently described in North Dakota, first read this BBC account, which is typical of the hundreds of news stories about the finds. Next read this long but entertaining story in The New Yorker. Finally for a more mixed (and realistic) appraisal, read this news article in the journal Science. It is becoming a fascinating scientific and cultural narrative. [Update: Another  perspective on this story.]

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