B6 Fossils (page 79) Flashcards
What are Fossils?
they are the remains of organisms from may thousands of years ago.
Where are Fossils found?
they are found in rocks.
What can Fossils tell us?
they can provide the evidence that organisms lived ages ago.
They can tell us a lot about how much or how little organisms have changed (evolved) over time.
How do Fossles form in rocks?
They form in rock, in one of three ways:
1) From gradual replacement by minterals (most fossils happen this way)
2) From casts and impressions
3) from preservation in places where no decay happens.
Explain how fossils form from Gradual Replacement by Minerals?
Most fossils happen this way.
Things like teeth, shells, bones etc, which don’t decay easily, can last a long time when buried.
They’re eventually replaced by minerals as they decay, forming a rock-like substance shaped like the original hard part.
the surrounding sediments also turn into rock, but the fossil stay distinct inside the rock and eventually someone digs it up.
Explain how fossils form from casts and impressions?
Sometimes, fossils are formed when an organism is buried in a soft material like clay. The clay later hardens around it and the organism decays, leaving a cast of itself. An animal’s burrow or a plant’s roots (rootlet traces) can be preserved as casts.
Things like footprints can also be pressed into these materials when soft, leaving an impression when it hardens.
Explain how fissils form from preservation in places where no decay happens?
In amber (a clear yellow ‘stone’ made from fossilised resin) and tar pits there’s no oxygen or moisture, so decay microbes can’t survive.
In glaciers it’s too cold for the decay microbes to work.
Peat bogs are too acidic for decay microbes. (a fully preserved man they named ‘Pete Marsh’ was found in a bog).
(bogs are areas of land that are waterlogged and acidic - plants living in bogs do not decay fully when they die, due to a lack of oxygen. The partly decomposed plant matter accumulates over a very long periods of time and forma peat-a plant material which is partially decomposed)
Give some Hypotheses suggesing how life first came into being?
No one really knows how life first started, but there are various hypotheses.
Maybe the first life form cam into existence in a primordial swamp (under the sea) here on Earth.
Maybe simple organic molecules were brought to Earth on Comets - these could have then become more complex organic molecules, and eventually very simple life forms.
Hypotheses of how life first cambe into being can’t be supported or disaproved, why?
because there is a lack of good, valid evidence:
Many early forms of life were soft-bodied, and soft tissue tends to decay away completely - so the fossil record is incomplete.
Fossils that did form millions of years ago may have been destroyed by geological activity, e.g. the movement of tectonic plates may have crushed fossils already formed in the rock.
(tectonic plates are large slabs of rock that divide Earth’s crust, move constantly to reshape the Earth’s landscape).
Suggest what makes low-oxygen environments suitable for the formation of fossils (2 marks)
The microbes that cause decay can’t survive in low oxygen conditions (1 mark). so the dead organisms are preserved rather than decayed (1 mark).
