Today generations are roughly 15-30 years, but the older life gets the shorter it seems to live in the human timeline.
So between 3.8 BYA and now, how many generations have passed? I’m assuming with single celled organisms (which we were for most of our history) you had potentially thousands of generations per year.
You would have to know the specific timeframe of the evolution of each species, plus the average length of a generation in each species. Unknown, perhaps unknowable without a time machine.
The number of generations is going to be almost entirely determined by the time when life was just procaryotic (bacterial/archaea), which is the first 2 billion years or so. E. coli can divide every 20 minutes, which gives more than 26,000 generations per year. Now growth won’t be so fast all of the time, but for the sake of illustration we could say that during the first 2 billion years there were 26,000,000,000,000 generations of microbes.
Eucaryotic organisms evolved about 1.5 billion years ago. Let’s say the lineage that led to humans was unicellular for 1 billion years and had a generation time of one week. That gives about 50,000,000,000 generations.
Let’s say the lineage that led to humans became multicellular about 500,000 years ago (actually, it would have been somewhat earlier) and had a generation time of one year. That gives 500,000 generations.
So basically the number of generations since life became eucaryotic is trivial compared to the number when it was procaryotic. The number is so heavily dependent on the assumptions you make about the latter that it hardly matters what you plug in for the former.
So we can estimate that my great[sup]50,000,000,000[/sup]-grandfather was a eucaryote?
That’s very flattering, to be sure.
Did you mistype 500,000 years ago?
Sorry, that should have been 500,000,000 years ago.
Why can’t I find more info on this guy, the rodent like ancestor of all Mammals, from the time of the dinosaurs…
http://www.livescience.com/26929-mama-first-ancestor-placental-mammals.html
What do you want to know about it?
Note that this is not an actual animal, based on fossils, but instead a composite extrapolated from the traits of modern mammals. It is entirely hypothetical, so none of the information about it is actually verifiable.
Well, thats what I thought but I wasn’t sure. Thanks.
Here’s a link to the original article,which is free with registration. It’s pretty technical, but it will contain whatever information there is about the hypothetical animal.
Thanks :D:D:D
How many generations have had 23 pair of chromosomes?
Tim Urban’s Wait But Why post Meet Your Ancestors (All of Them), which I came across a year ago may help.
*Going back 1,150 billion generations and roughly 3.8 billion years, we arrive at the end of our line—the first living particle and the founder of all life on Earth. *
Generations : I did so by making rough generation length estimates based on the typical lifespan and age of reproductive maturity of the various species along the way. I began with 25 years for human generations, then 13 years for Australopithecus and advanced primates, five years for early tree primates, two years for rodents, lizards, fish, and worms, two months for jellyfish and sponges, and one day for single cell organisms.
I liked the pictures.