Starts With A Bang! » Evolution Ethan Siegel's blog/video blog about Cosmology, the Universe, and everything else Sat, 04 Apr 2009 20:12:38 +0000 en It Begins… Mon, 30 Mar 2009 20:22:00 +0000 ethan Well, it’s happening this week, folks! I’m going to make the move over to ScienceBlogs this week, and I will have a special good-bye video post this Wednesday.

In the meantime, to help you cope with your sadness, Ian O’Neill at AstroEngine has this week’s Carnival of Space, and I have an example of artificial selection for you, duck-style:

The ones who are good at navigating metal grates survive to adulthood; the others, not so much. Yikes.

Between Bird and Mammal Lies the 6th Sense… Mon, 23 Mar 2009 20:45:53 +0000 ethan This Australian “mammal” is one of the most bizarre creatures on Earth, having many of the characteristics usually reserved for either birds only or mammals only:

Ladies and gentlemen, the duck-billed platypus! Its most notable features are as follows:

1. It lays eggs. This is usually reserved exclusively for birds, reptiles, dinosaurs, etc. And these eggs are tiny! Mammals gestate with the eggs inside of them, giving birth to live young, but here’s a mammal that lays eggs!

2. It’s furry. Like mammals are — no feathers for this guy — the platypus is not only covered in fur, it’s got such a nice coat that it has historically been hunted for its fur!

3. It is venomous! This is extremely rare for mammals, and the platypus itself has three venomous compounds in it that are unique in all of nature to the platypus itself. The venom is emitted through a spur in the platypus’ foot, right around its ankle. And speaking of feet…

4. It has otter-like feet. Totally mammalian, you got it. On the other hand…

5. It has a duck-like bill. Totally bird-like, of course. On the other hand…

6. It has a beaver-like tail. Mammalian, I got it. I suppose we can go on and on, listing all the ways this animal is neither bird nor mammal, all of which I find fascinating. But this animal can do something that you and I cannot, no matter how hard we try. Your skin, your epidermal layer, is fantastic for sensing temperature, pressure, and pain. These three types of sensor suit us remarkably well, and allow us to experience all sorts of interesting sensations, like itch and ticklishness. But the platypus has us beat, because in addition to these, the platypus can detect electricity!

That’s right, the duck-billed platypus has the most sophisticated sense of “electroreception” of any mammal, allowing it to track its aquatic prey by locating where an electrical stimulus resulting from muscle contraction came from. Normally, we only see this in predatory fish, like I’ll show you in the image below:

But here it is, in a platypus! How cool of a sense is that?! So the next time someone tells you about “the sixth sense,” don’t think of ESP and don’t think of Bruce Willis, think about the platypus, an animal with a real sixth sense: the ability to detect electricity!

Because I want a sense like that…

How Quickly do Humans Evolve? Mon, 16 Feb 2009 21:35:50 +0000 ethan One of the worst arguments out there against evolution is that we can see micro-evolution, in simple organisms, but not macro-evolution, or evolution in large plants and animals with long lifetimes. Therefore, the faulty argument goes, since we haven’t observed it directly, there’s no evidence for it. Let’s take a look at the obvious flaw in this argument:

Scientific studies have only been around for a few human generations. Evolution takes many generations to have visible effects. Something like a bacterium can reproduce so quickly that in just a few months you can have in excess of a hundred-thousand generations! So it’s very easy to observe evolution for microorganisms, since we have so much generational time to see change over time. This is much harder in longer-lived organisms. In humans, for instance, a typical generation is about 25 years. So while you get millions of generations for a microorganism, you only get one for humans and only a handful for even small mammals. So that logic is completely faulty.

Nevertheless, perhaps we can, if we’re clever enough, find evidence for the evolution of humans in our history. Human history goes back a long time, and if we study it properly, perhaps we can find something that shows how human characteristics change over time. As reported on MSNBC, changes in human DNA (as shown from human skeletal remains) have occurred about 100 times more quickly in the past 10,000 years than at any time in human history:

John Hawks, a professor at UW-Madison (shout-out!), rejected the assumption that human evolution ceased roughly 50,000 years ago, and working off of a sample of 35,000 years of skeletons from all around the world, uncovered the following:

In Europeans, the cheekbones slant backward, the eye sockets are shaped like aviator glasses, and the nose bridge is high. Asians have cheekbones facing more forward, very round orbits, and a very low nose bridge. Australians have thicker skulls and the biggest teeth, on average, of any population today.

“It beats me how leading biologists could look at the fossil record and conclude that human evolution came to a standstill 50,000 years ago,” Hawks says.

By his account, Hawks’ theory of accelerated human evolution owes its genesis to what he could see with his own eyes. But his radical view was also influenced by newly emerging genetic data. Thanks to stunning advances in sequencing and deciphering DNA in recent years, scientists had begun uncovering, one by one, genes that boost evolutionary fitness. These variants, which emerged after the Stone Age, seemed to help populations better combat infectious organisms, survive frigid temperatures, or otherwise adapt to local conditions. And they were popping up with surprising frequency.

The general rule here, that I love, is “adapt to local conditions“. What’s one of the simplest adaptations to local conditions in any living organism? The ability to blend in with their environment. The most stunning example is probably the chameleon, which can even adapt to change its color to match whatever it’s up against:

Does this work in humans? Could our huge variety in skin color be due to local adaptations? And if so, could we use this as evidence for human macroevolution?

Well, as reported by NPR, the answers are yes, yes, and yes! According to their research, changes in human pigmentation take only 100 to 200 generations, which is as few as 2,500 years. They specifically cite India as their example, that a few thousand years ago, when they lived farther to the North, their skin was much lighter, and has darkened dramatically over the past few millennia as they’ve migrated back to the south, to warmer climates.

Now, here’s a kicker: we already know why changing pigment is important for humans! From the NPR article:

“Humans started in Africa,” Jablonski says, the part of Africa near the equator where it is intensely sunny with lots of ultraviolet light.

Ultraviolet light, or UV, in high doses can age the skin and damage the DNA molecule, which makes it harder to build a fetus. Not to mention that ultraviolet light can sometimes cause skin cancer.

On the other hand, if a human is plopped down in, say, Norway, where the days can be short and there is precious little ultraviolet light, this creates problems, too. All vertebrate animals need ultraviolet light to help produce vitamin D. Vitamin D helps us absorb calcium from our food to build strong bones. If we don’t get enough ultraviolet light, we’re less likely to survive to reproductive age to produce strong-boned babies.

Thus the dilemma: People who live in sunny climes around the equator have too much UV. People who move away from the equator eventually have too little UV.

In fact, take a look at this map of UV radiation on Earth. How well do you think it will match the native population of that area?

Breathtaking, isn’t it? According to UV data alone, Australian Aboriginals and Africans should be the darkest, people from northern Europe, Asia and Canada should be the lightest, and Native Americans, those from the middle east (like me, ancestrally), and equatorial Asia should be in between. Sound like any world that you live in?

But science is even cooler than just this. Because we can make a computer model to simulate how the evolution of something like pigment works. We don’t need to simulate melanin or anything that complex, we can do it for a single-celled organism. If you have 10 minutes (and if you’re at work, feel free to turn the sound off; it’s just music), have a gander at how this works:

And while you’re here, I’d like to point out two things. First, I was asked a while ago where to go for educational science information on physics, astronomy, the natural world, etc. The National Geographic Channel has been putting out some good stuff recently. It seems like practically every Sunday night, starting at 8 PM ET/PT, they have a really interesting new science program on. This past Sunday, they had a 3-part program called Known Universe, where they talked about some of the biggest, smallest, fastest, and most extreme things we’ve ever discovered or created in the known Universe. This is great and rare, because it actually addresses things we know for certain, not only speculative theories or those for which there’s insufficient evidence. Yes, they have discussions about what may come next, but they’re well-done and reasonable, and it’s the things we already know that’s the (well-deserved) focus of the show. I’m really happy about it, and I regret not advertising it sooner. But look for it; it’s worth watching.

And second, the new Carnival of Space is up, just in time for… uhh… next year’s Valentine’s Day? Happy Monday, folks.

Q & A: How to Fight Global Warming Fri, 26 Dec 2008 20:08:59 +0000 ethan People often write in wanting to know the answers to big questions. Earlier this week I got a message from kampfgestfj asking me about global warming. More to the point, he wanted to know the following:

Why are there still those that don’t believe global warming is affected by man’s input into the environment?

Now, I don’t have a good answer for this, because I don’t understand the reasoning behind denying mankind’s influence on global warming. For me, the scientific evidence is pretty straightforward: industrialization is at an all-time high, there are more pollutants in the atmosphere now than at any point in all of human history, and global average temperature has followed the trend of CO2 in the atmosphere over hundreds of thousands of years according to all reasonable tests of scientific rigor. (And yes, you have to include an appropriate time-lag of about 50-100 years for the full effects to be felt.)

But there is a new finding that I find absolutely delightful. Ever hear about the little ice age in Europe? A few hundred years ago, the temperature in Europe decreased by a little less than 1 degree Celcius, and remained that way for about 200 years. Have a look:

Well, we think we know why this happened. When the Europeans came over to America, the Aztec and Incan civilizations crumbled. This was due to many factors, including (and perhaps especially) disease. From when the Europeans came over in about 1500 to about 1600, the populations of the Incan and Aztec empires dropped by about 90%. This was about 9% of the world’s population, and it meant that about 500,000 km2 of land went from being used by humans to wilderness. At those latitudes, that means there was about 500,000 km2 of reforestation that occurred.

Now, as everyone knows, trees breathe in Carbon Dioxide and breathe out Oxygen. The researchers estimate that 10 billion tonnes of Carbon Dioxide was removed from the atmosphere by this reforestation, significantly contributing to the fall in global average temperature.

Even with accounting for volcanic activity and the Sun’s variation in intensity, the impact of humans, according to the study, was undeniably important. So if we want to fix our global warming problem now, what’s the answer?

Well, it’s simple. RE-forestation. This is a surefire way to remove significant amounts of CO2 from the atmosphere. But this is a huge policy problem: how can we not only keep humans out of habitable areas, how can we get humans to leave areas where they’re already living? We know the problem. We know how to fight it. We even know how to fix it. The big question is how do we make it happen?

And that’s one I don’t have an answer for, just hope that we’ll get it right, and soon.

Q & A: Why don’t Woodpeckers get Brain Damage? Wed, 10 Dec 2008 19:50:22 +0000 ethan Everyone knows how much fun it is to get repeatedly hit in the head. Just ask Oscar de la Hoya after his defeat against Manny Pacquiao last weekend:

Ouch. It isn’t just boxers, either. Every animal that experiences head trauma is susceptible to the following symptoms:

  • Abnormal level of consciousness
  • Differences in pupil size
  • Rigid limbs
  • Flaccid limbs
  • Unusual eye movement
  • Bleeding from the nostril
  • Bleeding from the ear canal
  • Seizures
  • Head tilt

But the worst thing imaginable to me that results from head trauma is brain damage. It’s our minds that make us who we are, and the idea of living without mine is completely horrifying. Look at how different a normal brain can be from a damaged one:

Out of all the animals I know of, there’s only one that repeatedly slams its head into a block of wood, over and over, day in and day out, for its entire life: the woodpecker.

A woodpecker moves so quickly that its tiny, 50 gram head absorbs 1,300 pounds of force every time it smashes into a tree! So why don’t woodpeckers get brain damage? There has to be something that prevents its brain from rattling around in its head and slamming against the skull around it, right? No, there isn’t. The woodpecker’s brain does rattle around in its head and smash into its skull. Yet it still emerges brain-damage-free. There are three special adaptations of a woodpecker that allow this to happen; let’s take a look.

1. Spongy skull bones — while humans have spongy bones mostly on the interior of large bones, woodpeckers’ skulls are extremely spongy. This means they can compress and help absorb the impact of the brain jostling around. It’s like smashing a brain into memory foam instead of into solid bone, and it reduces the force on the brain tremendously.

2. Large surface area — a woodpecker’s brain is tiny. This is actually a positive thing, because the smaller something is, the larger its surface-area-to-volume and surface-area-to-weight ratios are. If something has a bigger surface area, it means that even if the force is large, the pressure gets smaller, and this helps protect the woodpecker’s tiny bird-brain.

3. Woodpeckers peck in a straight line — this one is hugely important. If everything’s in a straight line then there’s no rotating or torquing of the brain, and therefore no tearing of the nerves in the brain. Hence, no brain damage the way that car crash victims experience it.

And those three things combined allow a woodpecker to escape from all their daily pecking activities without so much as a hint of head trauma. Isn’t evolution neat?

What, you were expecting some astronomy/physics today? Go check out the latest Carnival of Space to get your fix, done by Dave Mosher in a new video format, and I’ll see you all next time!

The Spark of Life Fri, 17 Oct 2008 23:56:18 +0000 ethan One of the most challenging questions in biology is understanding how life originated on Earth. How do you go from a non-living mixture of simple (and often volatile) gases to a living organism, capable of replicating and surviving? After all, even the most primitive prokaryotic cells today (below) are incredibly advanced compared with something that could simply survive and reproduce.

Well, the first experiments were done in the 1950s, by Stanley Miller. He took four simple gases that contain the elements found in life on Earth: hydrogen (the most abundant), ammonia (gives you nitrogen), methane (gives you carbon), and water (gives you oxygen). He then pumped electric sparks through them, simulating either a thunderstorm or the addition of energy, and saw what resulted.

The big surprise? Organic molecules, including simple sugars and amino acids, including five separate amino acids. But he did another experiment that he never published the results from: injecting hot steam into the mix. There’s a good reason for this, of course. There’s something on Earth full of noxious gases that also has lots of hot steam injected into it:

Erupting volcanoes have this same environment. A young Earth surely had active volcanoes, and what’s more, the conditions in those volcanoes are thought to be nearly identical to the conditions Miller simulated in his experiments all those years ago. What’s interesting? Miller’s results have just been analyzed and published after all these years.

The result? Let’s see what Jeffrey Bada, the lead scientist and a former student of Miller, had to say:

“We found not only did these make more of certain amino acids than in the classic experiment, but they made a greater diversity of amino acids.”

How much more? Instead of 5 types of amino acids, the new results showed 22 types of amino acids, including nearly all of the standard amino acids found in life today. What’s more? Volcanic eruptions are almost always accompanied by thunderstorms today, and the amino acids created were in far higher concentrations than without the injected steam.

Now, amino acids don’t necessarily mean life, but this is a huge step; we go from a noxious, poisonous environment to one teeming with the building blocks of life! I still don’t know how those building blocks assemble themselves into a living, self-reproducing organism, but this is a huge step forward, and it was taken, unknowingly, in 1952.

Enemies of Science from Within? Mon, 15 Sep 2008 19:35:04 +0000 ethan Ever hear statistics like “95% of scientists believe in evolution” and think about the other 5%? Evolution is one of the greatest scientific success stories of all time, and has revolutionized the way we perceive the history of life on our planet. For a little refresher, check out Carl Sagan’s take on it below:

But somehow, even if you exclude mechanical engineers, computer scientists, and everyone except life scientists and earth scientists, there are still hundreds in the United States alone who believe that creation science is valid. In the past, these claims have been (rightfully) dismissed as scientifically invalid, and have been successfully kept out of science classrooms.

And then came this howler from overseas:

Professor Michael Reiss says that if pupils have strongly-held beliefs about creationism these should be explored.

Rather than dismissing creationism as a “misconception”, he says it should be seen as a cultural “world view”.

Why is this a big deal? Because Michael Reiss is the Director of Education for the Royal Society, the UK’s National Academy of Sciences.

Now, I’m all for education. I’m all for teaching about the misconceptions that go along with it, about the scientific method, and about explaining how we came to know the things we now accept as scientifically valid. I’m even for investigating the mechanisms that are known for evolution and those that are still up for grabs.

But embracing creationism as a cultural world-view in a science classroom? If you think that’s a good idea, why don’t you google for ‘creationism world view’ and see what comes up?

Whatever your personal feelings are on the matter, it certainly isn’t fit for a science classroom. And it’s shameful to have an organization as influential as the Royal Society advocating a position that denigrates the fundamental value of science like this. There’s been a mild outcry over this, but this is absurd! Why do I contend this? Because “creation science” is the enemy of science, and when your enemy attacks you, you need to defend yourself and fight back, not to capitulate. Michael Reiss is right about some things, like this:

When young people ask questions about creationism in science classes, teachers need to be able to explain to them why evolution and the Big Bang are scientific theories but they should also take the time to explain how science works and why creationism has no scientific basis.

But he’s unconscionably naive when he thinks that statements like “science teachers should endorse creationism as a worldview” aren’t going to be used by ‘creation scientists’ as evidence that creationism is valid. After all, this position has now been endorsed by the Royal Society!

Science is about discovering how the natural world works based on evidence gathered from the natural, observable world. That is not up for compromise. If my remedial 6th grade class at Crispus Attucks middle school in Houston, TX from 2000 can remember that, then maybe the director of education at the Royal Society should be held to advocating at least those standards.

The Largest Carnivore Ever? Mon, 04 Aug 2008 19:30:05 +0000 ethan Alright, some of you who’ve been reading this site for awhile may remember this article about Godzilla, where one of the major problems with having an actual animal like Godzilla would be its actual size. Why? Because carnivores just aren’t that big.

If we look at the largest carnivore living today, you know what it is? On land, it’s a polar bear, and at sea, the great white shark. Seriously, those are the largest. A polar bear can weigh up to about 1,600 pounds and the largest great white ever found is 21 feet long and just over 7,000 pounds.

But if we look all throughout history, we found that dinosaurs were larger land carnivores. Animals like the Tyrannosaurus Rex, Gigantosaurus, and Spinosaurus were around 50 feet in length and weighed between 6 and 8 tons. Pretty impressive, right?

Yeah, right. Impressive, sure. Until now. Because new research shows that the megalodon has everything except the fictitious godzilla beat. The megalodon was a lot like a great white shark, except, as far as we know, it went extinct 1.5 million years ago. Oh yes, and it was huge. Try this on for size:

The megalodon was up to 52 feet long and weighed over 100 tons (!), over 30 times larger than a great white shark! Its diet is estimated to consist mostly of whales. And perhaps most impressively, it is anticipated to have had a bite force of between 11 and 18 tons, despite not having a jawbone (its jaw was made of cartilage).

And if 52 feet, 100 tons, and an 18 ton bite force doesn’t scare you, maybe this actual picture of a megalodon tooth will put this in perspective for you…

And with that, maybe Discovery Channel will finally show something besides sharks on my damned cable TV!

Timeline of Natural History - Part 3 Fri, 06 Jun 2008 19:04:11 +0000 ethan Remember what the biggest questions is that we ask ourselves as scientists: where did we come from, and how did we get here? Well, here it is, folks! The last part in my timeline for the natural history of the Universe. In part 1, we talked about what happened during the first 50 million years, from inflation to the formation of the first stars. In part 2, we went from the formation of the first galaxies to the formation of our Sun.

I now bring you part 3, from our Solar System to the evolution of the earliest humans. Let’s starts with a brief recap of the first two parts, and then let’s get right to it!

  1. 10-35 seconds: Inflation — stretching the Universe flat and smooth.
  2. 10-30 seconds: The Big Bang — filling the Universe with matter, antimatter, and radiation.
  3. 10-30 to 10-10 seconds: Baryogenesis — creation of more matter than anti-matter.
  4. New! 10-5 seconds: Confinement — the first protons and neutrons form.
  5. 3 minutes: Big Bang Nucleosynthesis — creates the nuclei of the light elements.
  6. 380,000 years: Recombination — creates the first neutral atoms and emits the cosmic microwave background.
  7. 50 million years: The Universe forms the first stars.
  8. 300-500 million years: The earliest galaxies begin to take shape.
  9. 900-950 million years: Reionization — the Universe becomes transparent to radiation as the neutral intergalactic atoms finally become ionized.
  10. 3 billion years: Galaxy Clusters form, clumping together in groups of hundreds or even thousands.
  11. 3.5 billion years: The Universe’s expansion rate changes, allowing us to first see the evidence for dark energy.
  12. 9.1-9.2 billion years: A dust cloud in a spiral arm of the Milky Way collapses to ignite nuclear fusion, forming our Sun. Welcome to part 3!
  13. 9.2 billion years: As the Sun is forming, a thin disk of matter remains around it, known as a proto-planetary disk.

    This matter eventually gets swept up into little balls, and forms the planets we know and love. Of the four inner planets, Earth is special; there were two relatively large balls (one about the size of Venus, the other about the size of Mars) that smacked into each other early on.

    After the collision, the big glob left over formed the Earth, and the debris that was kicked up eventually was formed, by gravity, into the Moon.

  14. 9.5 billion years: Dark Energy, the mysterious force driving today’s expansion of the Universe, becomes more important than matter in causing the Universe to expand.

  15. 9.7 billion years: The oldest rocks on Earth were formed. The rock is known as the Acasta Gneiss and can be dated by the zircons inside of it. It’s located in the Northwest Territory of Canada, and you can actually go there any time you like; just plan a trip to Slave Craton. The Acasta Gneiss looks like this:

  16. 9.9 billion years: The first life on Earth appears! We learn this from looking at very old rocks in Greenland, along the Isua Greenstone Belt. How do we know there was life just from looking at the rocks? Carbon abundances. Where there’s life (or biomass), there’s a different ratio of Carbon-13 to Carbon-12 than where there’s just plain ol’ rock. And these rocks, which we can date to be 3.8 billion years old, show a difference of a factor of 100 trillion in their Carbon abundances. That is some pretty strong evidence!

  17. 10.7 billion years: Mars dies! Sorry, all you fans of the Red Planet, who were rooting for life on Mars to do just as well as life on Earth. Despite possibly having oceans, life, and a thick atmosphere just like Earth, this is the end of the road for Mars. Because it’s so little, only 11% the mass of Earth, Mars’ core cools and ceases to be active, killing its magnetic field. This allows the Sun to strip Mars’ atmosphere away, causing the oceans to either freeze or boil, and ending the road for life on Mars.

  18. 12.5 billion years: Two huge leaps happen in evolution. First, Red Algae, the first multicellular organism evolves on Earth! (It only took 2.6 billion years.)

    And second, the first organisms with two different genders evolve! This step is huge, because sexual reproduction allows evolution to happen much faster than plain ol’ dividing and making a copy of yourself.

  19. 13.2 billion years: The Cambrian Explosion happens! After very few really interesting, large living things coming to be on Earth for the first 4 billion years, the Earth suddenly finds itself awash in life. Everything from starfish to crabs to boneless fish to worms, mollusks, and insects appears. And mixed in with all of that, one very special fish evolved: the myllokunmingia. This fish is special because it’s the first form of life to ever evolve with a spinal cord. Almost all of the advanced animals, including every amphibian, reptile, dinosaur, bird, and mammal, evolved from this fish. Here is its fossilized remains:

  20. 13.5 billion years: Pangaea breaks up! All the land on Earth was once united in one supercontinent, but volcanic activity deep inside the Earth keep things on this planet moving, and caused this land mass to break apart and drift. It was just a short 200 or so million years ago that they were joined together.

  21. 13.65 billion years: The dinosaurs go extinct! After a great asteroid impacts the Earth.
    We can see the evidence everywhere we look, because there is a separate geologic layer that’s a telltale sign of a worldwide catastrophe.

    Once those large predators are gone, these little tiny birds and mammals are free to inherit the Earth. And what did they do in not even a hundred million years?

  22. 13.72 billion years: They evolved the first hominids, giving rise to our favorite great apes, us!

And the rest, my friends, is history. I hope you enjoyed parts 1 and 2 as well, and now you know some of the most important events in the history of… well, history! Did you like it? Then go up to the top of the page, and digg or stumble it! This one is too good not to share.

What, you’re still here? I didn’t give you enough space stuff this week? You’re right, and I’ll make it up to you next week. In the meantime, head on over to this week’s Carnival of Space, where there should be enough to tide you over until next week!

Just one cell? Tue, 03 Jun 2008 16:05:18 +0000 ethan Yesterday, I wrote to you about what looks like the discovery of water-ice on Mars, along with the implications for life over there. And I said that if the same processes happened on Mars that happened on Earth, it meant that the most advanced life that ever evolved on Mars was a single-celled, asexually reproducing organism, most likely a bacterium:

Remember that life on Earth originated when the Earth was less than one billion years old. How do we know? Well, Earth is 4.5 to 4.6 billion years old, and the oldest rocks on Earth that we find are 3.8 billion years old. And they show evidence of life all the way back then! The first living organisms were probably extremely simple, capable of either generating energy from the Sun or feeding off of some other type of energy, and reproducing. The simplest way to reproduce is simply to make a copy of yourself:

The problem for evolving much more complex life on Mars is as follows:

  1. Evolution is very slow if all you do is copy yourself and rely on mutations. These organisms have to evolve a way to reproduce sexually (rather than asexually), and this takes a long time.
  2. The bacteria above (prokaryotes) are simple and boring, and aren’t really capable of doing anything other than feeding and copying themselves. A much more advanced type of cell, that actually performs multiple functions with specialized mini-organs, needs to evolve.

  3. In order to burn fuel efficiently, life needs oxygen. Young Earth and young Mars had very little oxygen in their atmospheres, and so it requires a long time for algae and other plant life to emit enough oxygen to change the global atmosphere.

But maybe the biggest challenge to Mars is that, unlike Earth, Mars only had about 1.5 billion years to do all of this before its core froze, its atmosphere boiled off, and its surface froze. The steps above take a long time. How long?

Well, to evolve a specialized cell (a eukaryote) took about 2 billion years of evolution on Earth, with the first eukaryotic cells appearing somewhere between 1.65 and 2.1 billion years ago. For those eukaryotic cells to then evolve sexual reproduction took almost another billion years, with the first evidence for sexual reproduction occurring 1.0 to 1.2 billion years ago. This also coincides with roughly the first multicellular organisms, which date to 1.2 billion years ago.

Once we have sex in the mix, we can evolve much more quickly. But what about Mars? Well, because Mars is only 1/2 the diameter of Earth (and only 11% of its mass), it only had 1.5 billion years to do all of this, because by 3 billion years ago, it had become the barren, dry, cold desert that it is today. So if we assume that life there followed the same path that it followed here, there was no complex single-celled life, no sexual reproduction, no multi-celled life, and certainly, nothing rivaling the Cambrian explosion that we all know and love.

We love you, Mars, and we all hope we find a history of life on your surface. But let’s be realistic about what we can expect: just the first few baby steps of what we had here on Earth.