tokens: the Orion disks dust content, as measured with ALMA, are comparable with those measured for Perseus with VLA observations ( Fig. 5 bottom panel): 16 and 45% for Class 0 and Class I, respectively. Figure 6 presents a different visualization of the distribution of exoplanet systems dust masses compared to the range of disk masses observed in Class 0 and Class I disks in Perseus. The conclusions of our work show that for the complete sample of disks in Perseus and with a large sample of known exoplanets, there is enough solid material in the Class 0 stage to explain the solid content in observed exoplanetary systems. This conclusion is consistent with Najita Kenyon (2014) and Greaves Rice (2011) but now with much more robust statistics. In recent years, several studies, specifically with the use of microlensing observations, have estimated that nearly all stars could host a planet of at least 10 M ⊕ ( Cassan et al. 2012 ; Suzuki et al. 2016 ). Very few cases and irreproducibility of microlensing observations suggest caution should be taken when extrapolating the results to all systems. It should be kept in mind that a large population of wide-orbit planets could pose a challenge to efficiency of planet formation even at the Class 0/I stage ( Najita Kenyon 2014 ). Actual timescales for the different phases of low-mass star formation are uncertain. Based on a statistical analysis of a population of protostars, it is estimated that the Class 0 evolutionary phase lasts for ~0.1 Myr after the beginning of the collapse, and the Class I phase ends when the protostar is ~ 0.5 Myr old ( Dunham et al. 2014b ). More recent estimates of the half-lives of the protostellar phases give Class 0 half-life values of ~0.05 Myr and ~0.08 Myr for Class I ( Kristensen Dunham 2018 ). Therefore, our results indicate the start of the planet formation begins less than 0.1 Myr after the beginning of the cloud collapse. This is consistent with the ages of the oldest meteorites in our Solar System ( Connelly et al. 2012 ). 4.3 The context of planet formation models It is worthwhile to put our empirical constraints on the solid mass reservoir in the context of planet formation models. Broadly speaking, planets can either form bottom-up through the assembly of smaller building blocks in the so-called core accretion scenario, or top-down in the gravitational instability scenario via direct gravitational collapse of the disk material. In the latter case (see Kratter Lodato 2016 for a review), planets need not contain rocky cores and we may therefore have overestimated the solid mass locked in planets. In addition, in this view planets form at the very beginning of the disk lifetime when the disk is gravitationally unstable, possibly at even earlier stages than we probe here. If this is the case, our observations do not put constraints on the mass budget required for planet formation since planets would already be formed in the disks we are considering. Our results are instead
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