How old is the Mississippi River?
Much younger than you would guess. The valley the upper river runs through was carved by meltwater from a melting ice sheet, less than twelve thousand years ago. The last dinosaurs died 66 million years ago — about 5,593 times longer ago than that.
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A river cut by melting ice
“Glacial River Warren, predecessor to the Minnesota River, carved out the river’s wide valley, as it carried the meltwater pouring from glacial Lake Agassiz, between 11,800 and 9,200 years before the present.”
U.S. National Park Service, Mississippi National River & Recreation Area — River of History.
Picture what that means. An ice sheet sat on North America, melted, and the water had to go somewhere. It went south in a torrent big enough to cut the valley the Mississippi still uses. The river did not carve that valley; it inherited it.
Real photograph · 228988681/Shutterstock.com · Shutterstock Standard (free image collection, API) License
Did dinosaurs drink from the Mississippi?
No. Not nearly. The gap is not close enough to argue about: the last dinosaurs are tens of millions of years back, and the river’s valley is a few thousand. Put the two on the same line and the river is a rounding error.
There would have been rivers in North America then — there are dinosaur fossils in rock that the database records as river channels, near Denver, and that page shows what was found in them. But they were not this river. Rivers are among the least permanent things on a landscape.
“How old is a river” is a trick question
There are at least three different answers and they disagree by millions of years. The water is billions of years old. The valley is about twelve thousand. The drainage — the fact that this part of the continent sheds its water southward at all — is older than either, and harder to date.
So this page quotes the one thing the source states precisely, which is the valley, and declines to convert it into a single headline number for “the river”. If you see a confident number anywhere, it is worth asking which of the three it is answering.
One more figure, because it is lovely and it is the site’s subject: the Park Service says “It takes about three months for water that leaves Lake Itasca, the river’s source, to reach the Gulf of America.” Three months to cross a continent — and then it evaporates, and does it again.
For teachers
For school
- The valley the upper river runs through was carved by meltwater from a melting ice sheet, less than twelve thousand years ago.
- The river did not carve that valley; it inherited it.
- There are at least three different answers and they disagree by millions of years.
Classroom prompt
“How old is the Mississippi?” This page gives three answers — the water, the valley and the drainage. Write each one on a card and put them in order from youngest to oldest. Which one would you call the age of the river, and why?
Extension: the Park Service dates the valley, not the river. Find a confident “age of the Mississippi” somewhere else and work out which of the three answers it is really giving.
Ages: the melting-ice story works from about seven; sorting the three kinds of “how old” suits pupils of about ten upwards. That range is our teaching choice for this page, not a curriculum claim.
Where this comes from
- The quotations
- U.S. National Park Service, Mississippi National River & Recreation Area, read . Material created by the National Park Service is generally in the public domain. The extinction date is the same figure used across this site, cited to the International Chronostratigraphic Chart.
- How sure is this?
- Dates like these are a reconstruction of events nobody watched, built from what the meltwater left behind, so they are estimates rather than exact and the source gives them as a range. This page does not convert that range into an age for the whole river, because the source does not, and because the three answers above genuinely differ.
Where next
Rivers from the time of the dinosaurs left rock behind, and what rivers did dinosaurs drink from? shows what was found in it. For a river cutting through rock far older than itself, read how old the Colorado River is, and every river on this site is gathered on the rivers page.