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02. Why did the dinosaurs die out?

VOLCANISM

Some questions we might ask are:

  • Was volcanic activity more common in the past particularly at the time of the extinction of the dinosaurs?
  • Did toxic volcanic gases settle on the Earth’s surface poisoning the dinosaurs?

To answer these questions we must understand something about the structure and history of the Earth. The Earth is very old. It formed about 4600 million years ago (Ma). Scientists believe it began as a ball of hot dust, rock and gas which took millions of years to cool and harden. Volcanoes spewed out hot lava and volcanic ash. The atmosphere was made up of carbon dioxide, hydrogen, ammonia, methane and some sulphur dioxide. There was little oxygen.
The Earth’s crust is not one continuous layer but is made up of a number of plates that float on the mantle underneath. Between 550 to 350 Million years ago, all the continents were joined together in one giant landmass called Pangea. Slowly over time the plates started to move apart. Pangea separated into two super-continents:

  • Laurasia – a northern landmass made up of North America, Greenland, northern and central Europe, and most of Asia, and
  • Gondwanaland – a southern landmass comprising Australia, Africa, Madagascar, South America, Antarctic, India and some parts of south Asia
QMSB TO CLARIFY IMAGE ALT By 130 million years (Ma) ago Gondwanaland had begun to break up. This divided the landmass into two sections, a western half made up of Africa and South America, and an eastern half including Antarctica and Australia. By 70Ma wide oceans had formed between Antarctic, Africa and India. Australia split from New Zealand. Rifting occurred between the southern margin of Australia and Antarctica and the latter drifted towards the South Pole. Image: Commonwealth of Australia (Geoscience Australia), Creative Commons Attribution 2.5 Australia Licence, BY.

By the end of the Triassic (200 Ma) these super-continents had separated. By the early Cretaceous period (130 Ma) Gondwanaland had begun to break up. Eventually Australia, which sits on the Indo-Australian plate, separated from Antarctica. This plate is now moving in a north-eastern direction at 5-6 centimetres per year.

These continental plates move gradually, sometimes colliding with each other or sliding over or under one another. The boundaries between plates are often sites of geological activity. Sometimes pressure builds up causing a break at weak points called faults. This may result in volcanic eruptions or shakings at the Earth’s surface. These are called earthquakes.

As the continental plates moved, did animals start to experience different environmental conditions? Would this have had any effect on the dinosaurs?

  • Was there a virus, microscopic parasite, or disease organism that infected some dinosaurs and spread to other populations?
  • Were other factors involved?
  • Was one of them from outer space?