{"id":536,"date":"2011-10-22T10:49:44","date_gmt":"2011-10-22T10:49:44","guid":{"rendered":"http:\/\/vandfam.net\/dev\/wordpressmu\/college\/?p=536"},"modified":"2011-10-22T10:49:44","modified_gmt":"2011-10-22T10:49:44","slug":"dawn-of-the-trees","status":"publish","type":"post","link":"https:\/\/collegearchive.unc.edu\/?p=536","title":{"rendered":"Dawn of the trees"},"content":{"rendered":"

[Story by Margarite Nathe, Endeavors<\/a> magazine]<\/em><\/p>\n

\"\"<\/a>
Patricia Gensel studies the world's oldest trees. Her samples prove that plants started developing woody structures 10 million years earlier than previously thought.<\/figcaption><\/figure>\n

Say you\u2019ve been scooped up and tossed four hundred million years back in time, back when the planet\u2019s landmasses are still huddled together and the deep, colossal ocean Panthalassa covers most of the globe. The Earth you\u2019ve landed on is laboring through its Devonian Period, a stretch of history famous for its huge armored fishes, wandering tectonic plates, and plummeting levels of carbon dioxide. You\u2019re probably uncomfortably warm and the air probably stinks of iron\u00a0sulfide.<\/p>\n

Once you dust yourself off and take a look around, you\u2019ll see a swampy landscape and horizon jagged with volcanoes. There\u2019s some vegetation near the water\u2019s edge, but no trees or forests. The tallest plants in the world are only a few feet high and they have no leaves and no roots \u2014 basically, they\u2019re primitive, fleshy shoots that suck water from the mud directly beneath\u00a0them.<\/p>\n

Now look down, close to your feet. See that little plant that looks like a bunch of green spines sprouting out of the ground? Its stems are made up of what might be the very first traces of wood on Earth. And the next person to lay eyes on them, after you, will be UNC biologist Patricia\u00a0Gensel.<\/p>\n

In the mid-1990s, Gensel and her husband checked in to a summer cottage on the Restigouche River in New Brunswick, Canada. They\u2019d been going there for years, armed with picks and shovels and geological hammers, and sometimes with a few students to help them dig. Together they would venture out to the shore to look for plant\u00a0fossils.<\/p>\n

\u201cIt\u2019s not light work,\u201d Gensel says. Summers there are hot, and once the couple found a place near the shore to dig, they had to crack through the top layer of rock and lug the pieces aside. Then they would switch to crowbars. Hours later, if they were lucky, they were prying bits of fossilized plants out of the\u00a0ground.<\/p>\n

On this particular day, they were trying a new, little-known spot that some locals had pointed out to them. It didn\u2019t look too promising at first \u2014 a layer of small-pebble conglomerate doesn\u2019t usually make for well-preserved plant fossils, Gensel says. But once they dug through that, they found an obliging layer of undisturbed, finer-grain sediment. It was full of fossils. Some of them, she saw, blazed with an orange tinge. Bingo<\/em>.<\/p>\n

The color was a sign that the rocks were hiding pyrite, a mineral that turns to orange iron oxide when it starts to break down. And where there\u2019s pyrite, there are well-preserved\u00a0fossils.<\/p>\n

To create the seal that will protect a plant over time, Gensel says, conditions have to have been just right back when the plant was buried. A certain pH and a lack of oxygen would help the cell walls of a decaying plant attract ions of some kind of mineral \u2014 usually silica, calcium carbonate, or pyrite. The cells would then fill with crystals, which can preserve the anatomy of the plant for hundreds of millions of\u00a0years.<\/p>\n

Gensel was excited. Intact plant anatomy doesn\u2019t come along every day. So they collected for hours and packed up the rocks to be sent back to her lab at\u00a0UNC.<\/p>\n

Eventually all the fossils were unpacked, sawed into sections, polished, mounted on slides, sealed in resin, and ready to be studied. When Gensel finally saw the ancient cell structures under her microscope, she was flabbergasted. Rows and rows of rigid, rectangular cells radiated outward from the center of the stem. She could almost have been looking at a cross-section of a modern-day pine sapling. But according to the spores present in the rock, her fossils were clearly four hundred million years old \u2014 a good ten million years older than the first plants scientists thought had developed woody\u00a0structures.<\/p>\n

The more Gensel studied the world\u2019s oldest wood samples, the more convinced she became that scientists\u2019 main theory about why plants made the adaptation is wrong. It wasn\u2019t for strength, she says. It was for\u00a0plumbing.<\/p>\n

For the past hundred years, scientists have said that plants probably began to develop wood for structural support, to help them grow taller and stronger. \u201cBut these early plants were tiny,\u201d Gensel says. \u201cIn trees, secondary tissue and wood help provide additional support, but these little plants didn\u2019t need that. I think some of these changes in anatomy are related more to water use, or hydraulic conduction, than to\u00a0support.\u201d<\/p>\n

Plants were having a hard time staying hydrated enough to photosynthesize during the Devonian Period, mainly because carbon dioxide levels were plummeting. \u201cThe problem is that when the CO2 <\/sub>levels drop, plants have to open their stomates longer to take up CO2 <\/sub>for photosynthesis,\u201d Gensel says. (Stomates are pores on the surface of leaves and stems that allow for gas exchange in plants.) \u201cAnd every time they open their stomates to take in CO2<\/sub>, they lose water, because they\u2019re more hydrated inside than out.\u201d Plants needed more and better water conduction, and the elongated cells called tracheids that Gensel found in her fossils do just\u00a0that.<\/p>\n

Some researchers say that temperatures in the Devonian were dropping along with carbon dioxide levels, stirring up glacial activity and periods of climatic waffling. We don\u2019t know all the specifics, but we know that things were getting rough for plants. They had to adapt. \u201cThat\u2019s when most major plant structures evolved,\u201d Gensel says. \u201cBy the end of the Devonian, we had forests, big trees, leaves, and even early seed plants. Most of the kinds of reproduction we know in plants today were present by the end of the Devonian\u00a0Period.\u201d<\/p>\n

The fact that a woody structure gave plants more architectural support may have been just a happy accident. But all the changes together allowed Earth\u2019s flora to reach soaring heights, expand away from the shorelines, and spread inland to cover the\u00a0planet.<\/p>\n

While that was happening, the Devonian Period was coming to an end. It wasn\u2019t pretty, especially for the water-dwellers. Some unknown catastrophe triggered mass extinctions for various brachiopods, trilobites, jawless fish, and other reef-builders swimming in Panthalassa\u2019s waters, and brought the Age of the Fishes to an abrupt close. The organisms living topside, though, were just getting\u00a0started.<\/p>\n","protected":false},"excerpt":{"rendered":"

Say you\u2019ve been scooped up and tossed four hundred million years back in time, back when the planet\u2019s landmasses are still huddled together and the deep, colossal ocean Panthalassa covers most of the globe. The Earth you\u2019ve landed on is laboring through its Devonian Period, a stretch of history famous for its huge armored fishes, wandering tectonic plates, and plummeting levels of carbon dioxide. You\u2019re probably uncomfortably warm and the air probably stinks of iron sulfide.<\/p>\n","protected":false},"author":4,"featured_media":537,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[17],"tags":[],"class_list":["post-536","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-natural-sciences-mathematics"],"_links":{"self":[{"href":"https:\/\/collegearchive.unc.edu\/index.php?rest_route=\/wp\/v2\/posts\/536","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/collegearchive.unc.edu\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/collegearchive.unc.edu\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/collegearchive.unc.edu\/index.php?rest_route=\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/collegearchive.unc.edu\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=536"}],"version-history":[{"count":0,"href":"https:\/\/collegearchive.unc.edu\/index.php?rest_route=\/wp\/v2\/posts\/536\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/collegearchive.unc.edu\/index.php?rest_route=\/wp\/v2\/media\/537"}],"wp:attachment":[{"href":"https:\/\/collegearchive.unc.edu\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=536"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/collegearchive.unc.edu\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=536"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/collegearchive.unc.edu\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=536"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}