end cretaceous mass extinction

• The presence of iridium is found all over the world in sedimentary rocks - these rocks are 66 million years old. This iridium boundary comes from an extra terrestrial impact at the end of the cretaceous. 
• Tektites are small natural glass spherules and are formed due to the impact of a meteorite. They do not travel far from impact sites. 
• The possible location of the crater is on the Yucatan peninsula in Mexico. 
• Shocked quartz is found in a layer after the cretaceous, due to the impact of meteorites. Under high pressures the structure of quartz is deformed along planes, these are called planar deformation features. 
• There was a very thin layer of soot from wildfires that could have been triggered by an impact. 
• A large tsunami deposited sea sediments on land at Mexico. 
• The meteorite contained gypsum and hit an area of shallow sea. Lots od sulphur was sent into the atmosphere on impact which blocked sunlight causing a rapid drop in temperature of 25ºc for 15 years. This disrupts food chains because plants could not photosynthesise. 
• Sulphur in the atmosphere caused acid rain, acidifying oceans and damaging plants. Marine organisms with calcite shells may have been dissolved. 
• The deccan traps erupted at the end of the cretaceous for 30,000 years causing a drop in temp for a short while and a long term temp rise. Each lava flow shows a slightly different inclination showing the rapid movement of India over a mantle plume. 
• Fossil record of dinosaurs is hard to interpret, looking at ammonites is more helpful. A global fall in sea levels caused a decrease in marine organism numbers. 
• The K-Pg boundary contains lots of fern spores. Ferns grow best without competition after extinctions. Suggesting a global lack of light. 
• There are theories that the short term impacts caused the mass extinctions and global warming from volcanic activity helped stabilise temps.