Plants of the Past Exploring Palaeobotany in Transition Year Student Guide Louise Bailey and Eileen Nertney PLANTS OF THE PAST Contents 1. What is Palaeontology? 3 2. The Rocks Around Us 4 3. Out on the Dig-Fossil Hunting 7 4. Early atmospheres and changing climates 12 5. What can plants tell us about the past? 23 6. Pores of Plenty-What can we learn from stomata? 29 7. Recreating life from fossils 33 8. Looking for fossils in your area 35 9. References 36 10. Additional Activity 38 11. Acknowledgements 39 2 PLANTS OF THE PAST 1. What is Palaeontology? In your history classes, you may have learned how archaeologists excavate the sites of ancient human settlements to learn how we lived in the past. A palaeontologist does a somewhat simi- lar job. Palaeontology is the study of ancient life. As living organisms die, they often leave traces of their existence in the form of fossils. Fossils are impressions of living organisms which are created when their remains become trapped in sediment or other materials. Harder body parts such as shells are more easily fossilised than softer components due to their resistance to decay. Plants as well as animals can become fossilised. In fact, some plant parts such as pollen and leaf cuticle are very resistant to decay and can persist for millions of years in the fossil record. Plants can also record much information about the conditions that were present during their lifetime. Fig 1.1 Fossil leaf of Lepidopteris ottonis, from the Late Triassic of East Greenland. © The Field Museum, GEO86362_01d Student Activity 1.1 Palaeontology web quest Use the web to find out the answers to the following:- • How old are the oldest fossils found on earth? • Which fossils are the most abundant? • Where are fossilised plants most likely to be found? • What name is given to someone who studies fossilised pollen? • What is the largest example of a fossil land plant ever found? 3 PLANTS OF THE PAST 2. The Rocks Around Us The study of rocks and earth processes over long periods of time is known as Geology. Ireland has many different rock types as it has been exposed to different environmental conditions and geological processes over time. Tectonic activity has caused Ireland to migrate across the globe, resulting in many different rock formations. Ireland has at different times been part of a large, dry continental desert, swampland, shallow seas and volcanic landscape. The oldest rocks in Ireland, found in Co. Donegal are 1,700 million years old! Sedimentary rocks are of the greatest interest to Palaeontologists as their formation provides the best conditions for fossilisation of plants and animals. Other materials such as coal or am- ber may also contain fossilised or preserved parts of living organisms. Sedimentary Rocks Sandstone Mudstone (shales) Limestone Formed when sand is depos- Formed when silt and clay Formed under sea from the ited and compressed sediments are deposited and calcified remains of marine compressed animals and plants Forms in deserts, rivers Formed in swamps and wet- Found in many shades of Reddish orange appearance lands grey, white and brown Unlikely to contain fossils Found in multiple shades of Chalky, powdery appearance due to conditions present at green, brown, black, grey time of formation i.e. dry Can be very rich in fossils Can become slimy when wet particularly Coquina variety Shales are mudstones that split into horizontal sheets Often contain traces of ani- mals’ activity such as burrows Table 2.1 Common sedimentary rocks found in Ireland 4 PLANTS OF THE PAST A R AGE PERIOD MAP MAIN ROCK TYPES ENVIRONMENTS TECTONIC EVENTS E COLOUR Ice Age: Ireland covered and shaped by ice. 1.8 Quaternary* C I O Lake & swamp: Mid-Tertiary clays and lignite deposited in Z large lake (the precursor to L. Neagh). O Clay Geology of Ireland Tertiary N North Atlantic rifting: Greenland separates from E Volcanoes: Vast amounts of basalt lava flood NE Ireland Europe as Atlantic rift extends northwards. 1:1,000,000 scale C during Early Tertiary. Basalt 65 Geological Survey of Ireland Chalk Shallow 'Chalk sea': Ireland is land area for much of time. Compiled by B. McConnell, S. Gatley & A. Sleeman. Cretaceous Pure limestone deposited in late Cretaceous shallow sea, probably over whole of Ireland. Simplified from the Geological Survey of Ireland 1:100,000 scale Bedrock Map Series (1993 - 2003) and the Geological C 144 I Early Atlantic rifting: American & European Plates Survey of Northern Ireland 1:250,000 scale Geological Map O 1. The Giants Causeway: Tertiary basalt lavas Z Sea basins: Mud and limestone deposited in early Jurassic begin to separate, forming Atlantic ocean between. O of Northern Ireland (1997). Z Jurassic shallow sea in NE, while rest of Ireland is land. Thick E accumulations of sediment as today's offshore basins M form. Shale & limestone 203 Ó Geological Survey of Ireland 2003 Extension: Marine basins around Ireland formed by stretching of the continental crust. Triassic Desert: Red sandstone formed in arid desert dunes and Photograph credits: 1- GSNI; 2- B. Long; 3- B. McConnell; playa lakes. Evaporite (salt & gypsum) in hypersaline lakes. 4- M. Pulsford; 5- C. MacDermot; 6 & 7- M. Parkes 250 Sandstone 'New Red Sandstone' Variscan Orogeny: Minor effects in Ireland of Permian River deltas & swamps: Sand and mud deposited in large mountain building in Central Europe. river delta systems advancing into sea. Coal formed in hot 298 swamps. N Sandstone & shale Tropical sea: Limestones deposited in warm tropical sea. 50km Carboniferous Limestone Advancing sea: Sand and mud deposited in shallow sea Sandstone & shale advancing from south to north over eroded Devonian 354 mountains. C I O Sandstone Mountains & rivers: Red sand and mud deposited among Z Devonian semi-arid mountains by large river systems. Subsiding O 'Old Red Sandstone' E basin in SW receives vast thickness of sediment. Acadian Orogeny: Mountain building as Iapetus 2. The Poisoned Glen: ice-sculpted Donegal granite A L finally closes, joining NW and SE halves of Ireland. 410 A P Ocean basin: Sand and mud deposited in narrow ocean Silurian Sandstone & shale basin and continental margins as Iapetus closes. 440 Sandstone & shale Ocean depths & Ring of Fire: Sand and mud deposited in Ordovician Shale & sandstone, 1 deep ocean by turbidity currents. Ring of volcanoes Grampian Orogeny: Mountain building and basalt & rhyolite around ocean formed above subduction zones metamorphism in NW as volcanic arc collides with continental margin when Iapetus begins to close. 495 Sandstone & slate Shelf sea: Sedimentary rocks deposited on continental Cambrian Quartzite in above shelf in SE. Iapetus ocean opens: Ancient continents rift apart 545 to form Iapetus ocean crust between. Schist & gneiss Ancient continents: Ireland's oldest rocks formed 1800- 1900 million years ago as igneous intrusions; Cadomian Orogeny: Metamorphism of oldest rocks 2 Quartzite in above metamorphosed to gneiss by Grenville mountain building. in the SE. Derry PRECAMBRIAN* Sedimentary rocks (Dalradian), including deposits of global Grenvillian Orogeny: Mountain building and ice age, formed at rifting continental margin in NW. metamorphism of oldest rocks in the NW. Letterkenny * Precambrian and Quaternary not to scale IGNEOUS ROCKS Kilroot Basalt, minor rhyolite - Tertiary Gap in geological record salt Volcanic rocks (no rocks preserved) Volcanic rocks - Precambrian to Carboniferous Working mine or pit Granite & gabbro - Tertiary Belfast 2 Photograph location Granite - Ordovician to Devonian Intrusions Cavanacaw gold Gabbro & related rocks - Ordovician Monaghan Sligo Ballina Dundalk Cavan Kingscourt gypsum 3. The Twelve Bens: Dalradian quartzite mountains Castlebar Navan zinc, lead 3 Tuam Mullingar Athlone Dublin Galway Tullamore 4. The Burren: karstic Carboniferous limestone 4 5 Ennis Galmoy zinc, lead Lisheen Limerick zinc, lead Kilkenny 5. The Cliffs of Moher: bedded Carboniferous sandstone Wexford Tralee Waterford 7 Mallow Killarney 6 Cork 6. Valentia tetrapod tracks: early 7. Booley Bay: striped Cambrian mudstones, an amphibian footprints preserved in Devonian sandstone important fossil site Fig. 2.1 A geological map of Ireland’s rocks. © Geological Survey of Ireland 2010 5 PLANTS OF THE PAST Student Activity 2.1 Identify a selection of sedimentary rocks using the key given below Identify a number of rocks collected in your local area or supplied by your teacher Test rock sample with dilute Hydrochloric Acid (HCl) 1. Rock reacts with HCl -If rock with visible fossils Limestone 2. Particle size -If particles are large, chunky and clearly visible go to 3 -If particles are small go to 4 3. Fragment shape -If particles made of angular fragments Breccia -If particles made of rounded fragments Conglomerate 4. Particle Grit -If particles are small, same size and gritty Sandstone -If there is little grit Siltstone -If no grit go to 5 5. Visibility of Layers -If no layers visible Mudstone -If layers visible and easily broken Shale -If sharp edges form when broken Chert 6. Black, visible plant debris Coal Safety: Dilute HCl is corrosive and can cause burns. Make sure you have your teacher’s permission when using HCl and always wear safety goggles. 6 PLANTS OF THE PAST 3. Out on the Dig-Fossil Hunting One of the first difficulties encountered by budding palaeontologists is trying to determine the age of a fossil. Fossils are often dated from the rock in which they are found using methods such as isotope analysis and radioactive element dating. The geological timescale of rocks covers a period of approximately 4.6 billion years. That’s a lot of rocks to date! Thankfully rocks are usually deposited in a fairly consist pattern in what are known as bedding planes. The oldest rocks are normally located at the bottom (deepest in the ground) and the newest at the top.