The Dinosaur Trial An Introduction to Science Peter Brøgger Sørensen, Aabenraa Gymnasium og HF Søren Kjær Sørensen, Skive Gymnasium og HF Denmark

Background Mass extinction at the Cretaceous – Tertiary Boundary. Approx. 70% of all species, including the dinosaurs, became extinct. Some claim the cause was an asteroid impact. Others claim heavy volcanism.

Purpose To introduce the scientific method where arguments are based on observations. To show science as: Exciting Debating Alive!

The framework A murder trial with two accused: An asteroid and a volcano. Observations are presented as witnesses. Students are the judges.

More Info Contact: Download this PowerPoint: soeren.kjaer.soerensen@skivegym.dk Download this PowerPoint: www.skivegym.dk/gis/trial.ppt

What killed the dinosaurs? The Dinosaur Trial What killed the dinosaurs?

What is a dinosaur? Reptile with a characteristic hip joint that enabled them to walk upright. Emerged in Triassic approx. 200 mio. years ago. Dominated the Earth in Jurassic and Cretaceous. Species of dinosaurs emerged and became extinct along the way, but NO Dinosaurs survived the transition to Tertiary approx. 65 mio. years ago.

A Dinosaur! Tyrannosaurus Rex. From Cretaceous. Notice the hip!

Geological Periods Geological periods are defined by characteristic sediments and fossils. Transitions are typically sudden. Transitions reflect a change in the global environment.

KT-boundary Transition from Cretaceous to Tertiary is called the KT-boundary (Cretaceous = Kreide). The KT-boundary is found at the surface of the Earth at different places – e.g. Stevns Klint. The age of the KT-boundary is 65 mio. years.

Stevns Klint south of Copenhagen Tertiary KT-boundary (Fishclay) Cretaceous

Accused: An Asteroid The Solar System is littered with asteroids. An impact of a 10 km asteroid will have global consequences.

Accused: A Volcano A volcano effects the environment by emissions of gasses and particles. Major eruptions have global effects.

1. Witness: Iridium Element no. 77 (platinum-group) Rare on Earth (0.01 mg/tonnes), but rich in cosmic materials (450 g/tonnes). It is assumed that the Earth’s Ir-content is compatible with that of cosmic materials, but that it is found in the interior of the Earth.

Iridium at Stevns Klint High concentrations of Iridium are found at the KT-boundary – world wide.

Ir came from an impact Cosmic material are enriched in Iridium. At impact an asteroid is evaporated, and the material is spread world wide. The amount of Iridium is consistent with the impact of a 10 km wide asteroid.

Ir came from a Volcano The Iridium is found deep within the Earth. The magma of some volcanoes originate from great depths. Some active volcanoes are known to emit Iridium in connection with their eruptions. Piton de la Fournaise on La Réunion in the Pacific.

2. Witness: Carbon Black Carbon Black is found everywere in the geological layers. Sources of Carbon Black: Wildfires Volcanoes Asteroid impacts

The Origin of Carbon Black The element Carbon (C) is found in 3 isotopes: 12C (approx. 99%) , 13C (approx. 1%) and 14C (very rare). The ratio between 12C and 13C varies. Δ13C is the ratio 13C/12C compared to 13C/12C i seawater. 13C

Carbon Black at Stevns Klint The Fishclay (KT-boundary) is black due to large amounts of Carbon Black. The Carbon Black starts 3.5 m below the Fishclay (the zone is called the grey-chalk). Fossil Bryozoans (moss-animals) show Carbon Black stained fossils on non-stained fossils, and vice versa.

Carbon Black at Stevns Klint

Carbon from a Volcano The Carbon Black came from regular volcano- eruptions over an extended period of time: 3.5 m at Stevns Klint is approx. 50.000 years. Bryozoans show the Carbon came in pulses. Δ13C matches a volcanic origin.

Carbon from an Asteroid Major asteroid impacts will ignite world wide wildfires. It is possible that the volcanic carbon black is mixed with carbon from wildfires at the KT-boundary: 13C

3. Witness: Fossils Geological layers often contain fossils. If the right conditions are present, the skeleton of some species are preserved as fossils. Dinosaur fossils are rare. Bones can be found in Hell Creek, Montana, and eggs in Southern France and Spain.

Hell Creek The KT-boundary is very near the top of the Hell Creek formation. Data covers 11 km2 of outcrop. 2324 bones from 985 individual dinosaurs were found. The pattern reflects the low probability of finding fossils.

France No clear KT-boundary. Dating by magnetostratigraphy. KT-boundary is in the end of C29R. Last dinosaur-egg is found in C30N approx. 1 mio. years before the KT-boundary.

Fossils Point at an Impact A major asteroid impact will suddenly change the conditions for life on Earth. The fossils at Hell Creek show that dinosaur extinction was sudden.

Fossils Point at a Volcano Volcanoes emit various different substances: For example: Se. A known effect of Se is that eggs enriched in Se have reduced hatching-efficiency. Data from France point at a gradual dinosaur extinction.

4. Witness: Chicxulub A buried crater on the Mexican Yucatan- peninsula. With a diameter of 170 km the 3rd largest known crater on Earth.

Why Chicxulub? Dated to 65 mio. years (the KT- boundary). The size indicates that the impact had global consequences. Minerals in impact-debris found at the KT-boundary are similar to minerals in the Yucatan soil.

Consequences of an Impact NOx formed during passage of the atmosphere (acid rain). SO2 and CO2 released from evaporation of target-rock. Material slung high into the atmosphere. Upon re-entry it ignites combustible materials. Small particles in the atmosphere block the sun for months. Photosensitises collapses.

5. Witness: Deccan Traps Area covered with lava in India covers approx. 1.5 mio. km2 contains 521,000 km3 of lava One of the largest lava- covered areas in the World.

Why Deccan Traps? The lava has an age of 65 mio. years (KT-boundary). The lava originates from great depths of the Earth’s mantel. 65 mio. years ago India was situated on top of the vulcano Piton de la Fournaise.

Consequences of an Eruption Gasses released to the atmosphere influence global temperature and result in acid rain. Poison compounds are spread and have global effect (like Se on egg-hatching). Particles slung high into the atmosphere block the sun for months – photosynthesis collapses.

What is your verdict? Or ??