New News Biology #59

Fossils & Extinction

Fossils are things left behind by long-dead organisms. It could be a skeleton made of rock, impressions in the ground, or organisms that haven’t decayed.

Most things that have ever lived are now extinct, but by looking at what they left behind, we can see how organisms have changed and find evidence for evolution.

Ways fossils form:

Gradual replacement (by minerals): things that decay really slowly can be replaced by minerals, resulting in rock-like substances that are completely identical to the original organism.

Casts + impressions: the organism is buried in soft material like clay, which hardens as the organism decays. We are left with a gap - the same size and shape of the organism. Impressions are like footprints, a mark on the ground

Preservation: there is no decay at all. Sometimes the organism gets into amber or tar pits, where there is no oxygen or moisture which means no decay. The same happens in glaciers, but the reason it doesn’t decay here is because glaciers are too cold for microorganisms. Peat bogs are also ideal as well, because it is too acidic for the microorganism.

The oldest fossils ever discovered are from 3.5 to 4 billion years ago, though we don’t have a complete fossil record (with periods in time where we don’t know what happened). We still have no idea how life first developed. The reason is that early life forms were soft bodied (which decayed quickly). Also, fossils formed that long ago would most likely been destroyed since, through natural events like volcanoes or earthquakes or larger geological activity (for example, movement of tectonic plates).

Extinction 101: we declare a species extinct when no individuals of that species remain. There are several reasons on why a species may go extinct:

The environment may change too quickly (habitat cut down, too warm, etc.)

A new predator arrives and kills them all

new disease (that spreads throughout the population)

New species out-competes them for resources like food and water.