The global carbon cycle is a conceptual tool we use to understand how much carbon is on the Earth, where it is, and how it flows between places. It affects life, from creating habitats for fish and animals to supporting agriculture that feeds societies. Previous work suggests that most of the carbon on land is locked up in soil (rather than plants, animals, or fresh water), and estimates there is about 1,500 gigatons of carbon in the top meter of soil on Earth. However, in some places, bedrock can be tens or hundreds of meters deep. We present an estimation of how much hidden carbon there is in soil and sediment beneath 1 meter. We combined a database of hundreds of thousands of soil profile measurements with other global datasets and made a model to predict how much carbon is underneath our feet. We estimate that the deep stock could be more than ten times bigger than current global estimates. While deep stocks are often ignored because they're assumed to not interact with the surface, we show how earth surface processes can bring deep soil up to the surface at substantial rates that are worth considering in global carbon models.