Re: What was the enviornment like before and after the extinction of dinosaurs?

Hi John,

This isn’t my area of expertise, so I asked a colleague. This is what Stephanie Kienast had to say:

The dinosaurs went extinct 65 million years before present. There is strong geologic evidence for a massive meteorite impact at precisely that time. A large impact crater has been found off Mexico. Iridium, an element of extra terrestrial origin, as well as ash and debris, were deposited worldwide at precisely that time.

The impact is thought to have lead to massive environmental change. The time before the impact, a geologic period called the Cretaceous, was generally warm, wet, and characterized by high sea levels. The impact is thought to have triggered a massive tsunami that flooded coastal areas. Even worse, the impact lead to debris, dust and ash clouds that darkened the skies, prevented sunlight from reaching the Earth surface. This interrupted photosynthesis and disrupted the food chain: 90% of all plankton species, 75% of all plant species, and all dinosaurs went extinct 65 million years ago.

The geologic time period that followed, the Tertiary, was cooler on average than the preceding Cretaceous. The gradual cooling during the Tertiary is not directly related to the impact, however, but to changes in plate tectonic configuration and ocean currents.

I hope this answers your question. Feel free to contact me or Stephanie if you have more questions about past climate or the ocean.

Cheers,
Tetjana