The Origin and Development of Life

One of the big questions - where did life come from? Geologists have contributed significantly to answering the question.


What the Syllabus Says - and the Details

Life probably originated from the oceans, 3,500Ma in black smokers or hydrothermal pools. This makes sense as both of these combine warmth, suitable chemicals and water to dissolve the chemicals in so that they could react together. The photo shows a black smoker - a vent on the base of the ocean where these hot chemicals are erupted.

The diversity of life evolved through single cells, multicellular organisms, animals with hard parts, fish, amphibians, reptiles, mammals, birds and humans.

You need to be able to use simple evolutionary trees diagrams (cladograms) to demonstrate evolutionary trends. The cladogram below shows the increasing diversity from single celled organisms such as bacteria and protactists to mammals and birds.

You need to be able to use the geological column to put dates on events in the evolution of life - for instance, use the geological column below to work out in which period and how long ago the first fish evolved.

The development of the life on Earth was in stages punctuated by times of major extinction events, for example the K/T mass extinction. This is summarised in the exercise below... (answers at the bottom - but how much do you remember?).

Mass Extinctions Summary

1.     A mass extinction is when ____________ _______ of the life on Earth gets wiped out by an event.

2.     There have been ________ mass extinctions that we know about.

3.     The worst mass extinction happened at the end of the ______________________ period around _____________ million years ago.

4.     The most well known mass extinction happened ___________ million years ago at the K/T ( ___________________ / __________________ ) border. This was the extinction event that wiped out the _____________________ .

5.     The three known causes for a mass extinction event are: -

a)    A __________________ impact.

b)   A very large _______________________ eruption.

c)    Anything which floods the sea with __________________ _________________ so that the creatures in it are killed through a combination of poisoning and a rise in _______________________ .

6.     One theory for how the K/T extinction occurred is that the Earth was struck by a __________________ . This would have produced a very large cloud of ___________ that went into the __________________________  blocked out the ________________ and therefore caused most green plants to ______________ . This would have meant that the animals had little to ____________ and so most also ________ .

7.     Two good bits of evidence for this impact are; a very large impact crater in ________________ and a layer of _____________ rich sediment. ________________ is very rare on Earth and must have come from ____________ .

8.     A problem with this theory seems to be that the layer of ___________ rich sediment from the _______________ _____________ is found about _____ __________________ years after the death of most of the ________________ .

9.     An alternative theory for the K/T extinction is that it was caused by a massive volcanic eruption in a region called the ______________ ______________ in India. This would have sent a very large cloud of ___________ that went into the __________________________  so the same things happened as after the ________________ _________________ .

There is an alternative theory that the extinction was caused by the ______________ ________________ followed by the ______________ _______________ event. Any large creatures, like dinosaurs, would then have had a period of about two _____________________ years in which they were struggling for food, so extinction was almost inevitable. An advantage of the K/T mass extinction was that it allowed the group of animals called _________________ to develop, which in turn meant that humans could evolve.

Answers... almost all, 5, Permian, 225, 65, Cretaceous, tertiary, dinosaurs, meteorite, volcanic eruption, carbon dioxide, temperature, meteorite, dust, atmosphere, sunlight, die, eat, die, Mexico, iridium, iridium, space, iridium, meteorite impact, 2 million, dinosaurs, Deccan Traps, dust, atmosphere, meteorite impact, meteorite impact, Deccan Traps, million, mammals.

Of course - it is possible that neither of these two theories is actually the right answer. These type of questions are tackled by 'academic research geologists'. They follow the standard scientific method...

• decide on a question they want to find an answer to and suggest a testable hypotheses

 • seek evidence to test whether that hypothesis seems to work

• develop conclusions from the evidence collected

• get their work reviewed by other academic geologists 

• publish results

They will also review the work of their peers (other academic geologists) so that everyone is helping everyone else to improve their work.