Great news!
A spacecraft has found definite signs of life on a habitable world!
Well, it was Earth and the craft was a probe named Galileo that flew past its home in 1990 for an equipment check before sailing on to explore the Solar System as far as Jupiter. (Here’s how that turned out.)
This isn’t from Galileo, but it is definitely cool. In 2020 NASA turned some of its data on Earth into music and released the video. Check out which instrument is “playing” atmosphere, water, etc., at the YouTube page.
Still, congratulations to the rocket scientists!
And even though our focus is on how cats evolved, we do need to look at Earth and ask the basic questions: where did it come from? What makes our planet such a good stage for, and cast member in, that ensemble play we call Life?
Only then will details in later chapters make sense, for instance, why cats have four legs and a long tail (mammal predators do have other options); the whole cat-dog thing and whether T. Rex ate any of their direct ancestors; why cats have pretty fur but scary claws and teeth (compared to our own flat fingernails and chompers), and so forth.
The evolutionary processes — or tools, from a metaphysical standpoint — that have led to all of this are very powerful.
The Galileo probe could never make such a spectacular find: possible traces of 4.1-billion-year-old life, preserved in an Australian zircon crystal. (Image: Figure 1, in Bell et al., PNAS, open access)
They are ancient, too, coming into play soon after the planet’s formation, as we saw in earlier chapters with LUCA (the last universal common ancestor of all life, including those 3.5-billion-year-old fossil cyanobacteria we mentioned that aren’t much different from cyanobacteria living in stromatolites today).
The life these processes shaped over deep time might have branched off at any moment into something totally different.
But it didn’t.
There is this Earth and there are these living beings called Order Carnivora.
How did that happen?
Let’s begin at the beginning, and then carry on the interesting story — part of what experts have managed to piece together and agree on, anyway — through the next few chapters.
Some of this is iffy, but I’ll try to stay as close to the current consensus as possible.
About that consensus…
Unfortunately, the details of Earth’s earliest days aren’t very well known. Evidence from those times is rare in the geological record, and difficult to interpret. (Taylor and McLennan; Zahnle et al.)
As you’ve probably heard, current thinking is that there was a vast cloud of nebulous interstellar dust that collapsed some four and a half billion years ago — around the 4,500-Ma line in our cat/sports field analogy.
This event formed the Solar System and the Sun (which is actually a star).
Scientists agree on that.
Chondrites sometimes also contain carbon. Check out the photographer link for lots more information. (Steve Jurvetson, CC BY 2.0)
The boffins even have some leftover “construction debris” to prove it: chondritic meteorites, chunks of solidified nebular material that were too heavy to be pushed out of the neighborhood by the new Sun’s stellar wind but were too small to grow into planets through gravitational attraction.
Scientists may soon get a chance to watch this happen at another solar system hundreds of light-years away.
There’s a lot of such debris still floating around out there, but it’s mostly out of our reach.
So an insane amount of science has been done on the chondrites that essentially fell into our laps, as well as on the two most accessible relicts of Solar System formation — Earth and the Sun (the Moon formed a little later, as we’ll see in the next section).
This work has been verified and expanded upon with data collected through high-tech ground-based astronomy as well as by space missions to other Solar System bodies over the last half-century or so, all of it processed on incredibly powerful computers.
Spacecraft get spectacular closeups, but there’s a special thrill to standing your back yard, looking into an eyepiece, and seeing our neighbors in real time, just hanging out. This was taken during the Great Conjunction of December 2020, by Steve Fung, CC BY-SA 2.0.
For example, experts now know that brand new giants like Jupiter and Saturn had enough mass, 4.5 billion years ago, to capture some of the solar nebula for their atmospheres and then to hold onto this material — mostly hydrogen, water vapor, methane, and ammonia — as the brightening young Sun blew away the remaining free-floating nebular gas. (Olson and Sharp; Zahnle et al.)
Let’s call this Point A: Consensus on how the Solar System formed.
While everyone is okay with the big picture, scientists from assorted fields obsess and argue over many of its details.
Earth in space: One of the biggest mysteries in the Universe. (Image: 19 Studio/Shutterstock)
Of course they do: that ancient cloud of dust is all there was to work with.
How could something like that turn into Life and our “blue marble”?
Are we unique, or does this sort of thing happen throughout the Universe (and if it does, why haven’t we spotted other life yet)?
Point B is obvious, as the Galileo probe showed in 1990: Earth today, with continents and oceans full of life.
We need to get from Point A to Point B.
It’s quite a challenge. And the trickiest part comes first.
Read the whole thing
Featured image: slowmotiongli/Shutterstock
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