One of the biggest changes on Earth during the Cretaceous period was the continuation of Pangaea's separation. By the time the Cretaceous period hit, Earth had separated into many smaller continents.
The Chicxulub impact crater, shown below, caused the mass extinctions of the dinosaurs and many other life forms. Only a few organisms survived.
The crater was roughly 110 miles across and debris from the explosion was thrown into the atmosphere altering the climate. The same soil around the Gulf of Mexico contains deposits of boulders that generated a large tsunami.
There were tropical plants, ferns, and flowering plants during this time period.
Insects began to diversify during this period, such as butterflies and ants. Snails, clams, amphibians and certain types of mammals moved through this time period with few or no extinctions.
Dinosaurs were present during this time period until an asteroid hit the earth and caused them to go extinct. A few examples were theropods, confuciusornis, and the iguanodon.
During this period the climate was warmer and the sea levels were higher. There was also no ice that existed at the poles. Due to the separation of Pangaea, however, the global climate cooled.
The Cretaceous period was during the Mesozoic era and the Phanerozoic eon. It was the last and longest period of the Mesozoic era.
The cretaceous period atmosphere was richer in oxygen than the earth is now.
The origin of the name Cretaceous is Latin and characterized by the extinction of the dinosaurs. The Cretaceous is named after its chalky rock deposits that were found in England.
This period created forests that are our present day forests and generated coastlines that are also still present today.
Sources
http://www.ucmp.berkeley.edu/mesozoic/cretaceous/cretaceous.php
http://www.livescience.com/29231-cretaceous-period.html
https://www.psi.edu/epo/ktimpact/ktimpact.html
https://earth.usc.edu/~stott/Catalina/Cretaceous.html
http://www.ucmp.berkeley.edu/diapsids/extinctheory.html
http://staffweb.nsd.org/tley/dw_pp/malcolm_pp/assets/cretaceous_earth.jpg
ghttps://media1.britannica.com/eb-media/44/136144-004-76AAB173.jp
http://www.sciencemag.org/sites/default/files/styles/article_main_large/public/images/gg_60212W_Crater.jpg?itok=U5HowQh7
http://www.rocksinmyheadtoo.com/Pangea.jpg
http://simplebooklet.com/publish.php?wpKey=1gjPMzt0u9PUUqmamhXwsW
https://www.bobvila.com/articles/fern-gardening/
https://www.pinterest.com/fernworld/fern-fossils/
http://www.dailymail.co.uk/sciencetech/article-3480222/Searching-life-mass-extinction-Scientists-plan-drill-crater-left-asteroid-killed-dinosaurs.html