NARRATOR：

Listen to part of a lecture in a geology class.

MALE PROFESSOR：

Since Earth formed, some four and a half billion years ago, the number of minerals here has increased dramatically, from a few dozen relatively simple minerals early on...to over 4,300 kinds of minerals we can identify today-many of them wonderfully complex.

A basic question of geology is how all these new minerals came into being.

Well, recent studies have turned to biology to try to explain how this happens.

[word unstressed] Now, much of biology is studied through the lens of evolution.

And the theory of evolution suggests that, as environments change-and inevitably they do-some organisms will have characteristics that allow them to adapt to those changes successfully...characteristics that help these organisms develop and survive and reproduce.

And when environments become more complex-as tends to happen over time-those earlier adaptations, those variations...become the basis of yet other combinations and variations... and lead to ever more diverse and complex forms of life.

So from fewer, simpler, and relatively similar forms of life billions of years ago,life on Earth has now become a dazzling array of diversity and complexity.

Well, some geologists now want to apply this concept to explain mineral diversity too.

The conditions that minerals are under are not constant.

Conditions like temperature or pressure or chemical surroundings-these change-often in cycles, increasing and decreasing slowly over time.

And as conditions change, minerals sometimes break down and their atoms recombine into totally new compounds,as part of a process some call mineral evolution.

Now, minerals are not alive, of course, so this is not evolution in quite the same sense you'd have in living organisms.

But there do appear to be some parallels.

Living organisms not only adapt to their environment but also affect it-change the environment within which other organisms may then develop.

Likewise, each new mineral also enriches the chemical environment from which lots of other, even more complex new minerals may be formed in the future.

Beyond these similarities, though, what's really fascinating about mineral evolution is the way minerals apparently coevolve with living organisms.

Uh, what do I mean by that?

Well, it's maybe a billion years after Earth's formation that we first see evidence of life.

Of course, early life-forms were primitive-just tiny, single-celled microbes-but over time, they had a profound effect.

Huge numbers of these microbes began producing food by photosynthesis, which, of course, also freed up enormous amounts of oxygen.

And lots of that oxygen interacted with the atoms of existing minerals, creating rust out of iron, for instance, reacting with a whole range of different metals to create lots of new minerals.

Now, living organisms rely on minerals.

But they not only take in some minerals as nutrients, they also excrete others as waste products... including what we call biominerals-minerals that form with the help of biological life.

We can see geologic evidence of biomineral production in what are called stromatolites.

Stromatolites look like wavy layers of sedimentary rock.

But they're really fossils- fossils of the waste from microbial mats.

Microbial mats are vast colonies of one-celled organisms... that were once the most prevalent form of life on Earth.

And the study of stromatolites indicates that these ancient microbial mats interacted with minerals in the environment and left behind new compounds as waste products-biominerals like carbonates, phosphates, and silica.

In fact, we've grown microbial mats in the laboratory, and, over time, they too have produced some of the same sorts of minerals found in stromatolites.

Uh, you don't need to know the details of the process right now- we're still figuring out just how it works, ourselves.

But you might be interested to know that this concept of mineral evolution is being used in the search for evidence of life on other planets.

The thinking is that if certain minerals occur here on Earth as a result of a biological process, and if we also find those same minerals on another planet,this would suggest that life may have once existed there.

But-just because a particular mineral is found on say, Mars or Venus- uh, we really shouldn't assume that whatever caused it to turn up there...must be the same process that formed that mineral here on Earth.