The 366 daily episodes in 2014 were chronological snapshots of earth history, beginning with the Precambrian in January and on to the Cenozoic in December. You can find them all in the index in the right sidebar. In 2015, the daily episodes for each month were assembled into monthly packages, and a few new episodes were posted. Now, the blog/podcast is on a weekly schedule with diverse topics, and the Facebook Page showcases photos on Mineral Monday and Fossil Friday. Thanks for your interest!

Friday, April 11, 2014

April 11. Land life


On March 9, back in the Ordovician, we talked about life invading the land. But I think you need to not think of it as an invasion, but more of a gentle encroachment. There wasn’t much beyond moss-like plants and algae, maybe some fungus, and we really only know about them from spores.

It wasn’t until the Silurian that we find “real” plant and animal fossils that are definitely from land-dwellers, including air-breathing animals. Plants had to evolve mechanisms to maintain water once they were out of the sea. That included a skin of sorts, to keep the water in, and pores to manage the water content. By the Silurian, plants were developing vascular systems to send water (and the nutrients it carried) here and there throughout their bodies. Plants called Cooksonia and related varieties are the oldest such plants we know.  They’ve been found in Silurian rocks of Wales and England.

The first true air-breathing animals were things like millipedes and centipedes, and possibly spiders and scorpions – all arthropods. The oldest of all is called Pneumodesmus, and it’s a probable millipede from Scotland that lived about 428 million years ago, about the middle of the Silurian Period. It was discovered in 2004 and there’s only one specimen – but it has structures that indicate it was an air-breather. It would take 50 million years before the first vertebrate came ashore to live – during the Devonian, which we’ll get to next month.
—Richard I. Gibson

Silurian life

Photo by Xenarachne via Wikipedia under Creative Commons license

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